ArticlePDF AvailableLiterature Review

Abstract

Several studies have demonstrated a decline in the male reproductive system, sperm quality, and fertility with advancing paternal age, yet many of the biological mechanisms that underlie this process remain poorly understood. It is unclear whether the problem arises from the progenitor spermatogonial stem cells (for example, from an accumulation of DNA damage and mutations), from the somatic niche present in the testis (consisting of Sertoli and peritubular myoid cells), or from a combination of the two. Current data, albeit from a small number of studies, suggest that both factors have a role in age-associated germ cell loss. What is clear, on the other hand, is that mounting evidence links paternal age to chromosomal damage and genetic problems in the children of older fathers. The frequency of de novo mutations increases markedly with age, leading to increased risk of breast cancer, cardiac defects, developmental disorders, behavioural disorders, and neurological disease in the children of older men. The current trend towards fathering children at a later age raises concerns regarding the risk of offspring developing complex multigene diseases.
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Department of
Pharmacology and
Therapeutics,
McGillUniversity,
3655Promenade
Sir‑William Osler,
Montréal, QCH3G 1Y6,
Canada (C.Paul,
B.Robaire).
Correspondence to:
B. Robaire
bernard.robaire@
mcgill.ca
Ageing of the male germ line
Catriona Paul and Bernard Robaire
Abstract | Several studies have demonstrated a decline in the male reproductive system, sperm quality, and
fertility with advancing paternal age, yet many of the biological mechanisms that underlie this process remain
poorly understood. It is unclear whether the problem arises from the progenitor spermatogonial stem cells
(forexample, from an accumulation of DNA damage and mutations), from the somatic niche present in the
testis (consisting of Sertoli and peritubular myoid cells), or from a combination of the two. Current data, albeit
from a small number of studies, suggest that both factors have a role in age‑associated germ cell loss. Whatis
clear, on the other hand, is that mounting evidence links paternal age to chromosomal damage and genetic
problems in the children of older fathers. The frequency of denovo mutations increases markedly with age,
leading to increased risk of breast cancer, cardiac defects, developmental disorders, behavioural disorders,
and neurological disease in the children of older men. The current trend towards fathering children at a later
age raises concerns regarding the risk of offspring developing complex multigene diseases.
Paul, C. & Robaire, B. Nat. Rev. Urol. 10, 227–234 (2013); published online 26 February 2013; doi:10.1038/nrurol.2013.18
Introduction
Growing evidence suggests that male reproductive func-
tion declines with age and that ageing is associated with
decreased sperm quality. Spermatogenesis is a highly
coordinated multistep process, involving the prolifera-
tion and differentiation of spermatogonial stem cells
(SSCs) into mature motile sperm. During this process,
germ cell DNA is replicated and exchanged during
homologous recombination. At this time, the cells are
vulnerable to the introduction of a range of errors. If
these cells are not eliminated by apoptosis, then any
errors incurred could not only compromise the survival
of the germ cells but, if not repaired, could be passed
on to offspring. Indeed, the age of male partners cor-
relates with decreased germ cell number and, hence,
reduced testicular weight,1,2 decreased sperm motility,
and abnormal morphology,3–6 as well as reduced preg-
nancy rates and increased time to pregnancy.7–11 Paternal
age is also linked to chromosome damage and to genetic
problems in the children of older fathers. With advanced
paternal age, there is an increased incidence of struc-
tural chromosomal aberrations and a greater risk of new-
borns developing complex multigene diseases.5,12,13 For
example, studies have established increased incidences
of autism14 and schizophrenia15 in the offspring of fathers
aged >50years (Table1).
Although some of the studies listed in Table1 have
been criticized for not adjusting for confounding factors
(such as female age and coital frequency), others have
taken these factors into account and still shown that
older men exhibit reduced fertility. One such study
reported that men aged >45years demonstrated a five-
fold greater mean time to pregnancy than men aged
<25years.10 However, most fertility studies of older men
divide patients into just two arbitrary age groups—for
example, men aged <45years and ≥45years—with
only a small number of studies powered to support a
true linear relationship between age and fertility-based
parameters. Thus, most studies fail to pinpoint a true
threshold for the decline in fertility, potentially leading
to the development of inaccurate clinical guidelines for
couples trying to conceive. In this Review, we discuss
published data relating to the effect of paternal age
on reproductive factors such as sperm quality, fertil-
ity, time to pregnancy, pregnancy loss, and congenital
defects in offspring.
Advancing age and germ cell loss
New generations of spermatozoa develop continuously
in the seminiferous epithelium of adult males. Thus, all
germ cells that leave the testis have been dividing and
differentiating for a relatively short period of time—
between 35days (in mice) and 70days (in humans),
depending on the species.16 On this basis, people used
to think that male germ cells were always freshly made
and were, therefore, largely unsusceptible to the effects
of ageing. However, we now know that the precur-
sor cells that give rise to male germ cells act as stem
cells and are present throughout the lifespan of each
indivi dual. Anumber of studies have investigated how
sperm quality is affected by advancing age. However,
it is not yet known whether decreased sperm quality is
the result of continual division of the SSCs to produce
germ cells—resulting in an accumulation of damage
that, in turn, results in the production of poor quality
sperm—or whether the surrounding Sertoli and myoid
cells create an environment of decreasing quality with
advancing age. For example, age-related reductions in
Competing interests
The authors declare no competing interests.
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the number of Sertoli cells17 or altered gene expres-
sion could render these cells unable to support germ
cell development (Figure1). However, several clini-
cal studies—as well as preclinical studies of animal
models—indicate that substantial changes to germ cells
and mature spermatozoa occur as males reach a more
advanced age (usually around age 18months in rodents
and age 40years in humans) and that these changes have
consequences for their progeny.
Two main characteristics of ‘testis ageing’ are loss of
germ cells—for example, as a result of testicular regres-
sion or atrophy—and an increasing abundance of Sertoli
cell only (SCO) tubules.18–20 Supporting cell populations
also change, leading to reduced numbers of Sertoli and
Leydig cells.17,21,22 So how does age affect the function of
SSCs and the cells they rely on for survival and develop-
ment? A handful of studies have attempted to establish
whether the effects of ageing—such as germ cell loss and
the accumulation of DNA damage in sperm—result from
DNA damage accumulation in the continually dividing
stem cells or from defects in the supporting somatic cells
(Figure1). Interestingly, the number of undifferentiated
spermatogonia has been shown to dramatically decrease
with age,23 possibly suggesting that either their ability to
divide during mitosis is impaired with age or there is an
accumulation of damage too significant to be repaired
and these cells are thus lost. By transplanting SSCs into
the testes of both young and old mice, Zhangetal.24
demonstrated that the number of functional SSCs per
testis and the quality of the remaining SSCs in atrophied
testes significantly declined with age. When young SSCs
from mice aged 2–6months were transplanted into the
atrophied testes of mice aged 1year and 2years,
the 1-year-old testes could support the regeneration of
spermato genesis, whereas the 2-year-old testes could not.
The study investigators concluded that both the quan-
tity and quality of SSCs decline with age and that the
somatic environment is significantly affected.24 However,
another group, who also used transplantation of SSCs to
determine age-related alterations, concluded that there
was no change in SSC function with age.25 However, this
group studied mice that were only 1year old, whereas
Zhangetal.24 showed age-related differences in 2-year-
old mice. There were also strain differences between
these studies, which should not be overlooked.
An additional study has shown that changes in the
stem cell niche are responsible for the age-related
decline in stem cell number.26 This study demonstrated
that, in Drosophila melanogaster, the somatic niche cells
in the testes of older males displayed reduced expres-
sion of DE-cadherin (a cell adhesion molecule) and a
key self-renewal signal protein called unpaired protein.
The study investigators showed that these expression
changes were linked to germ cell loss by forcing the
expression of unpaired protein in niche cells. This tech-
nique prevented the loss of germ stem cells in ageing
males, suggesting that a decline in the function of the
stem cell niche is responsible for age-related germ cell
loss in D.melanogaster.26 Ryu etal.20 also concluded that
failure of the SSC niche causes diminished fertility in
Key points
Male reproductive function declines with age, as evidenced by decreased sperm
quality and increased time to pregnancy
The quality and quantity of spermatogonial stem cells seems to decline
withage, undoubtedly affecting the quality of germ cells and, ultimately, sperm
Alterations in DNA repair pathways in the ageing male occur concomitantly
withobservations of increased DNA damage in germ cells and mature sperm
Ageing males display increased rates of denovo mutations, which are linked
toan increased risk of diseases such as autism and schizophrenia in offspring
Table 1 | Clinical studies of paternal age‑associated genetic disease in offspring
Disorder in offspring Supporting study Study design
Developmental disorders
Achondroplasia Orioli etal.108 Birth defects register
Apert syndrome Tolarova etal.87 Birth Defects Mentoring
Program registry and
Centerfor Craniofacial
Anomalies registry
Crouzon syndrome Glaser etal.109 Patient records and
population census
Marfan syndrome Murdoch etal.110 Inpatient register
MEN2A Schuffenecker
etal.111
Large tumour study register
MEN2B Carlson etal.112 Direct clinical evaluation
Pfeiffer syndrome Glaser etal.109 Patient records and
population census
Neurological disorders
Alzheimer’s disease Bertram etal.96 Direct clinical evaluation
of healthy volunteers
and outpatients attending
memory disorder clinic
Autism Hultman etal.14 Population‑based
medicalregistry
Behavioural/mental disorders
Bipolar disorder Grigoroiu‑
Serbanescu etal.94
Direct assessment of
admitted patients with
bipolar 1 disorder
Bipolar disorder Frans etal.93 Nested case control study
(hospital discharge
registerand
multigenerational register)
Schizophrenia Dalman etal.95 Inpatient register
andparishregister
Schizophrenia Sipos etal.15 Inpatient discharge register
and medical birth register
Congenital cardiac defects
Ventricular septal defects,
atrialseptal defects, and patent
ductus arteriosus
Olshan etal.97 Health Surveillance registry
Right ventricular outow tract
obstruction and pulmonary
valvestenosis
Green etal.98 National Birth Defects
Prevention Study (multicentre
case control study)
Cancer predisposition disorders
Breast cancer Hemminiki etal.858 Family Cancer Database
and Statistics Sweden
Breast cancer Choi etal.113 Patients with breast cancer
versus healthy volunteers
Cancer of the nervous system Hemminiki etal.85 Family Cancer Database
and Statistics Sweden
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older mice, rather than a reduced ability of the SSCs to
self-renew. These investigators proposed that SSC self-
renewal would continue beyond the normal lifespan of
an individual.
Age-dependent modifications of the germ cell epi-
genome remain relatively poorly understood; however,
many of these modifications influence gene expres-
sion during embryogenesis and the postnatal period,
explaining some of the paternal age effects that have
been demonstrated previously. Altered gene-specific
DNA methylation patterns have been identified in
the aged somatic tissues of many mammalian species,
including humans.27 With increasing age, gene methy-
lation status increases for a number of systems within
the human body, including the testis, lung, liver, blood,
and stem cells.28–31 If hypermethylation were to occur
during ageing in SSCs, it seems logical to assume that
the ageing process would be accompanied by a loss
of develop mental c apacity—for example, as a result of
reduced numbers of maturing germ cells. This effect has
been demonstrated in mice; haematopoetic stem cells
(HSCs) from older animals display increased stem cell
self-renewal, but decreased ability to differentiate.32
A number of cell cycle proteins have potential roles in
ageing and germ cell loss. For example, the gene Cdkn2a
encodes various different transcripts, such as p16INK4a
and p19ARF, which are involved in cell cycle regulation and
cellular senescence.33,34 Both p16 and p19 are quiescent
during development and postnatal life, but their expres-
sion increases markedly with advancing age in many
tissues. Mice that are genetically modified to carry either
one or two additional copies of the INK4/ARF locus
demonstrate impaired production of male germ cells.
In fact, those with two additional copies exhibit an SCO
phenotype, with complete absence of sperm.35 Evidence
suggests that repressed expression of p16 and p19 could
help to promote the self-renewal of stem cells in young
tissues.36 Expression of these proteins increases with age,
perhaps contributing towards a decline in stem cell func-
tion. However, it is still unclear—especially in relation to
the ageing testis—whether p16 and p19 act as pro-ageing
or anti-ageing factors.35 Although a number of studies
have been published on the role of stem cell ageing, more
in-depth studies are needed to determine exactly where
and when the problem arises in the ageing testis.
DNA damage accumulation in testis
Under normal circumstances, DNA repair machinery is
required for meiotic recombination and for the correc-
tion of DNA damage in developing germ cells.37 Germ
cell DNA is constantly under attack from endogenous
and exogenous factors that can induce a wide range of
DNA lesions. These lesions are formed during normal
processes (such as transcription, recombination, and
replication) or induced by external influences, such
as irradiation, chemicals, and reactive oxygen species
(ROS). Germ cells have the ability to produce high
levels of ROS,38 which can generate a variety of DNA
lesions. One of the most abundant lesions, 8-oxo-2'-
deoxyguanosine,39 is strongly mutagenic and blocks
transcription. However, the testes possess a complex
antioxidant defence system,40 in addition to normal
DNA repair systems. Approximately 150 genes have
been identif ied in humans that are involved in protect-
ing genome integrity,41 including those involved in mis-
match repair, nucleotide excision repair, single-strand
break (SSB) repair, double-strand break (DSB) repair,
and base excision repair (BER). Proteins involved in all
of these p rocesses are expressed within the testis.42
Several lines of evidence suggest that male germ
line genomic stability declines with age. Although it
is not clear if damage is initiated in the SSCs or accu-
mulates in germ cells during spermatogenesis, ageing
seems to coincide with the number of SSBs and DSBs
in human sperm.43,44 An age-related decrease in levels
of apoptosis has also been reported in sperm, which
could partly explain observed increases in the total
number of sperm with DNA damage. ROS concentra-
tions increase with age, concomitantly with decreases
in antioxidant levels.45,46 Under normal circumstances,
maturing sperm in the epididymis generate low levels
of ROS via a capacitation-related process that involves
a redox-regulated tyrosine phosphorylation cascade.47,48
However, age-related imbalances between the generation
of ROS and the activity of the antioxidant defence system
can compromise DNA integrity and fertilization capa-
city (Figure2).49,50 ROS generation has also been associ-
ated with failure to remove residual cytoplasm, which
can result in premature release and loss of sperm func-
tion.51 In support of this model, a greater proportion of
sperm showing cytoplasmic droplet retention has been
observed in aged Brown Norway rats compared with
their younger counterparts.6 ROS-induced oxidative
DNA
damage
Spermatogonia
Spermatogonial
stem cells
Supporting niche
Accumulation
of DNA damage
in SSCs is passed
on to developing
germ cells
Supporting niche is unable
to support SSCs and germ
cells causing germ cell loss
and production of abnormal
germ cells
‘Selsh selection’ of
SSCs exhibiting
mutations leading to
clonal expansion of
‘mutant’ cells
Spermatocytes
Spermatids
Spermatozoa
Mutation
Figure 1 | Schematic representation to depict the role of SSCs and the supporting
niche in testis ageing within different scenarios. In scenario 1, the SSC is
compromised with DNA damage, which is transmitted to the developing germ cells
and mature sperm. In scenario 2, the stem cell niche in the testis ceases to
function to its full capacity and, therefore, the germ cells that are supported by this
niche decrease in number and are of lower quality. In scenario 3, rare mutations
arise in aged SSCs encoding gain‑of‑function proteins and are selected for during
clonal expansion of mutant SSCs. It is likely that all scenarios have a combined
effect in the ageing testis. Abbreviation: SSC, spermatogonial stem cell.
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stress can cause damage to mitochondria and result in
mutated mitochondrial DNA.45 Using techniques such
as the sperm chromatin structure assay (SCSA), chromo-
mycin A3 assay (CMA3), and Comet analysis,43,52,53
researchers have demonstrated reduced chromatin integ-
rity in the sperm of ageing males (Table2). Additionally,
investigators have reported a twofold increase in the fre-
quency of segmental duplications, deletions, and breaks
in the 1q12 site of sperm chromosome 1.13 On the other
hand, some studies have shown no age-related changes
in levels of DNA fragmentation.54,55
Relatively few studies have investigated levels of DNA
damage in early germ cells, such as spermato gonia,
spermato cytes, and round spermatids— presumably
owing to the technical difficulty associated with isola-
ting pure populations of these specific cell types. These
limited studies suggest that DNA alterations are present
at the spermatocyte stage. In one murine study, mutation
frequency increased sevenfold in pachytene spermato-
cytes and 10-fold in round spermatids in aged cells
(28months) compared with young cells (2months;
Table2).56 In addition, aneuploidies are detected at a
greater frequency in the spermatids of ageing mice than
in younger mice.57,58 In humans, data have been con-
flicting. Although some studies indicate an age-related
increase in the acentric fragments of chromosomes,59
others have found no association between sperm aneu-
ploidy and age.53 In hamster spermatids, an increase in
micronuclei has been detected in older males, indicating
increased chromosome loss.60 A higher index of arrested
germ cell divisions has also been observed in the testes of
older men.59 These study investigators identified abnor-
mal cells with structural disorganization in regions of
the seminiferous epithelium where spermatocytes would
normally be present, suggesting a dysfunctional blood–
testis barrier. However, an alternative explanation is that
meiotic arrest occurs after DNA damage.
Alterations in DNA repair activity have also been
observed in older males (Figure2). One murine study
demonstrated a decline in BER activity with age, which
coincided with reduced β-polymerase expression (at the
protein and RNA levels) and activity.61 Another study
reported ≥50% reductions in the BER activity of nuclear
extracts from mixed germ cells extracted from mice aged
24months. BER activity was limited at different repair
stages in older mice (24months) compared with younger
mice (4months). In this study, BER activity was limited
by uracil-DNA glycosylase expression in younger males
and by apurinic/apyrimidinic endonuclease expression in
older males.62 Using the Brown Norway rat ageing model,
we have also shown a reduction in BER mRNA and protein
levels,63 which could partly (in addition to increased ROS)
account for increased DNA damage in older sperm. In
addition, we have demonstrated an increase in levels of
8-oxo-2'-deoxyguanosine, not only in the testes, but also in
sperm.63 Although one study has reported increased BER
protein expression in older men, these men were attending
an andrology clinic for procedures such as orchidectomy
for prostate cancer64 and, therefore, the findings could be
confounded by other factors.
In terms of other DNA repair pathways, rat data show
that DSB repair is compromised in older males in various
tissues.65,66 In the testis, one of the key components of
this repair pathway, Ku80, is significantly downregulated
in older males.67 Reduced DNA repair would lead to an
accumulation of DNA damage in the germ cells of older
males, which would be exacerbated by the concomitant
reduction in antioxidant capacity (Figure2).
Implications of delayed fatherhood
Although it is now well accepted that sperm quality
influences fertilization and embryo development, there
is still some debate regarding whether DNA damage con-
tained within the sperm chromatin can be passed on to
the embryo and cause adverse effects to the offspring,
or if the damage is repaired by the oocyte after fertiliza-
tion. Several DNA repair and damage response genes are
expressed in the early mammalian embryo,42 but many
are expressed at low levels, explaining the limited ability
of embryos to repair DNA damage.68 Some studies have
shown that human and rodent sperm with DNA damage
are still capable of fertilization,69 but DNA originating in
the sperm introduces genomic instability to the embryo
and can have fatal effects on the development70,71 and
later life72,73 of the offspring.
Older men find it more difficult to achieve full-term
pregnancy with their partners, owing to the pathologies
associated with testis ageing. Partners of older fathers
both struggle to conceive7,8,74 and have an increased
Young male
ROS scavenging by
antioxidant defence system
Ageing male
Decreased antioxidant
defence system
Normal levels of
DNA damage
Increased levels of
DNA damage
DNA repair initiated
Normal sperm Sperm with
DNA damage
DNA damage not recognized and/or
compromised DNA repair
Normal healthy offspring Decreased pregnancy rate and
increased risk of genetic disease in offspring
Figure 2 | Schematic representation of the effect of ageing on male germ cells.
Defects in ROS scavenging and DNA repair give rise to the production of abnormal
sperm in older males, resulting in decreased pregnancy rates and offspring with
an increased risk of genetic disease. Abbreviation: ROS, reactive oxygen species.
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risk of miscarriage.75 The incidence of stillbirth also
increases with paternal age, but only when maternal age is
≥30years.76 Despite these observations, there is a trend in
some societies to have children at a later age, with a 40%
increase in the number of men aged 35–40years father-
ing children within the past 20years in the USA.77 The
increasing availability of assisted reproductive techno-
logies (ART), such as invitro fertilization (IVF) and
intra-cytoplasmic sperm injection (ICSI), is creating more
opportunities for men to father children later in life. Thus,
it is imperative that we understand the possible outcomes
of paternal age on the health and wellbeing of offspring.
A number of studies have examined age-dependent
changes in male factor fertility; however, results vary
depending on the age of the female partner. This vari-
able has resulted in, or contributed towards, some reports
of exceedingly high time to pregnancy rates. Another
factor to take into consideration is whether the study
cohort includes men attending fertility clinics, as this
could introduce bias. Additionally, time to pregnancy
rates do not account for failed attempts at conception.
Of note is one large well controlled study of the relation-
ship between male age and time to pregnancy, which
recruited participants without predetermined fertil-
ity problems and controlled for the age of the female
partner.10 This study found that increasing male age was
positively correlated with a significant decline in fertil-
ity. On average, men aged ≥45years experienced a five-
fold longer time to pregnancy than men aged <45years.
Other studies have shown that an increased time to preg-
nancy is evident in men aged ≥40years.7,80 However, it is
important to remember that such studies are susceptible
to selection bias. That is, men who have children later
in life could also represent different subgroups of men
(biologically and socially); for example, men who have
children later in life might be of generally better health
and the true effects of ageing might, in fact, be far greater
than predicted.
Increasing use of ART has led to concerns that using
sperm with damaged DNA for ICSI or IVF could have
long-term effects on the health of children born to sub-
fertile couples.78 In one IVF clinic, men aged >50years
demonstrated significant decreases in blastocyst forma-
tion and live birth rate compared with men ≤50years,
although pregnancy and implantation rates were
un affected.79 Sperm DNA fragmentation affects the post-
implantation development of the embryo and has also
been associated with early pregnancy loss.80
Animal studies in our laboratory have shown that
ageing has clear effects on progeny outcome, including
increased preimplantation loss, decreased fetal weight,
and increased postnatal death rate.81 Although no
substantial changes were reported in the frequency of
resorption, live offspring, or external malformations, a
threefold increase was noted in the risk of preimplan-
tation loss in litters fathered by old (age 24months)
versus young (age 3months) Brown Norway rats. In
these animals, increasing paternal age was directly
associated with a significant decrease in average fetal
weight. In addition, there was a threefold increase in
the number of neonatal deaths for progeny fathered by
older males. These data clearly indicate that the quality
of s permatozoa decreases as males age.81
A number of retrospective studies have investigated
the association between paternal age and progeny
outcome in humans.82–84 The average mutation rate for
older men was greater than for females of the same age83
and similar studies have shown an increased incidence
of a large range of genetic diseases in the offspring of
older fathers (Table1).83–84 Furthermore, other research
groups have established a strong association between
increasing paternal age and the incidence of breast
cancer and cancers of the nervous system; however, a
decrease was observed with certain other cancers (colon
and thyroid).85,86 Reports have also linked paternal age
with an increased incidence of fathering children with
autosomal- dominant genetic disorders, such as Apert
syndrome (RR = 9.5),87 Crouzon syndrome (RR = 8), and
achondroplasia (RR = 8–12).83,88 The age at which the risk
increases depends on the disorder; however, it ranges
from 30–50years of age.89 Achondroplasia, the most
common form of dwarfism, is caused by an auto somal
dominant mutation in the fibroblast growth factor3
(FGF3) gene and was the first recognized genetic dis-
order to be associ ated with increased paternal age.90 After
controlling for the age of the mother, this study demon-
strated a significant positive correlation (+0.273) between
p aternal age and the incidence of achondroplasia.
Advancing paternal age is also thought to increase
the risk of progeny incurring denovo mutations in
susceptibility genes for neurological and behavioural
disorders, including autism14 and bipolar disorder, as
observed in a number of clinical studies.91,92 Researchers
have demon strated an increase in denovo copy number
variants with advancing age in male mice.93 One study of
denovo mutations in an Icelandic population showed a
clear relationship between mutation frequency and age,
with the rate of paternal mutations estimated to increase
by 4.28% per year.94 Several other diseases of complex
aetio logy have been associated with a paternal age effect,
including schizophrenia,95 Alzheimer’s disease,96 and
cardiac defects (Table1).97,98 In animal models, altered
behavioural patterns—for example, altered exploratory
social behaviour99 and increased anxiety100—have also
been observed in the offspring of older fathers. Reduced
neurocognitive function has also been reported in
Table 2 | Summary of the ageing effects reported in germ cell studies
Study Ageing effect Species
Lowe etal.58; Xiao etal.57,58 Increased frequency of aneuploidies Mouse
Walter etal.56 Increased spontaneous mutation frequency Mouse
Schmid43 et al. Increased DNA damage in sperm Human
Zubkova etal.52;
Wyrobeketal.53
Altered chromatin integrity in sperm Human
and rat
Sloter etal.13 Structural aberrations of chromosome 1 Human
Miething etal.60 Arrested germ cell division Human
Cabelof etal.61;
Intanoetal.62; Paul etal.63
Altered DNA repair pathway efciency Mouse
and rat
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the offspring of older fathers101 and there is evidence
to suggest that daughters born to older fathers have
decreased longevity.102,103 Many autosomal dominant
disorders that show paternal age effects are caused by
base substitutions in genes with observable phenotypes.
For example, six conditions—achondroplasia, Apert
syndrome, multiple endocrine neoplasia (MEN) 2B,
MEN2A, Crouzon syndrome, and Pfeiffer syndrome—
have been linked to single base substitutions in the
FGFR3, FGFR2, and RET genes of the paternal genome.83
Notably, in a study of 154 patients with achondroplasia,
153 patients had a glycine to arginine substitution (150 of
which were guanine to adenine transitions). These muta-
tions in older men and their offspring could accumulate
as they are passed down through generations.104
Conversely, leukocyte telomeres are longer in the off-
spring of older fathers and this effect is amplified with
each subsequent generation.105 This finding could be
attributed to increased telomere length in the sperm of
older men106 and is thought to be an adaptive mecha-
nism, whereby information regarding the newborns
environment (in this case, a higher reproductive age)
can be passed on to future generations. The fact that
a father’s age has been shown to affect semen para-
meters, fertility, and the presence of congenital anoma-
lies in his children suggests that the genetic integrity
of otherwise- healthy sperm deteriorates with time
(Figure2). Increased mutation frequency in the sperm
of older men is most likely caused by a combination of
replication errors, epigenetic mechanisms, alterations
in apoptotic events, and compromised genetic defenses.
Associations between the presence of congenital con-
ditions and paternal age could be explained by ‘selfish
selection’, whereby spermatogonial cells that exhibit
mutations are preferentially selected, leading to their
clonal expansion (Figure1).107 Studies that have aimed
to quantify the number of mutations in sperm that are
directly related to paternal age-associated disorders
suggest that a common factor is the dysregulation of
spermatogonial cell behaviour, which is regulated by
the growth factor RAS signal transduction pathway. The
data show that most of these mutations encode proteins
with gain-of-function properties that are positively
selected for by the clonal expansion of mutant cells in a
process similar to oncogenesis.84 A relative enrichment
of these mutations ensues in sperm as a result of clonal
expansion in the normal testis, leading to an increased
risk of fertilization by mutant sperm.
Conclusions
With an ageing population that, increasingly, is choos-
ing to delay parenthood, concerns regarding the poten-
tial risks of a paternal reproductive age effect must be
addressed. Despite variation in the methodologies used
by many relevant studies, it is now clear that paternal age
correlates strongly with decreased sperm motility, abnor-
mal morphology, decreased pregnancy rates, increased
time to pregnancy, and increased incidence of genetic
disease in the offspring of older fathers (Table1). In light
of these findings, the American Society of Reproductive
Medicine (formerly the American Fertility Society)
introduced a guideline in 1990 to prevent men aged
>50years from donating sperm. Subsequently, this age
limit has been reduced to >40years.114
An explanation for this observed effect has yet to be
elucidated. It is unclear whether mutations are present
in the SSCs (and then carried through the developing
germ cells to the mature sperm) or the problem arises
later on (for example, during one of the germ cell stages
of spermato genesis). Regardless, various studies have
demon strated a link between the incidence of denovo
mutations in children and paternal reproductive age.
Further investigation is needed into the speci fic mecha-
nisms that occur during ageing (resulting in DNA
andchromatin damage) and the degree to which chemi-
cal and environmental factors can exacerbate or protect
indivi duals from such damage. Well-designed epidemio-
logical studies are needed—as well as further studies
using animal models—to fully understand the effect of
paternal age on progeny outcome. Data from these studies
could affect guideline recommendations for c ounselling
couples on the risks of conceiving at an older age.
Review criteria
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“telomeres”, and “germ cells”. The search was limited to
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and 2012. The reference lists of selected papers were
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Author contributions
Both authors contributed towards researching,
writing, discussing, and editing the manuscript.
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... This high level of genetic fidelity in part explains why even after exposure to chemotoxic agents or radiation in men, no increase in the incidence of birth defects, sperm DNA chromatin abnormalities or de novo germline mutations are noted in their offspring (104,105). In contrast, paternal aging has been shown to be unique for the creation of de novo mutations in male germline (106). Several mechanisms of age-induced de novo germline mutations have been proposed. ...
Article
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Paternal age at conception has been increasing. In this review, we first present the results from the major mammalian animal models used to establish that increasing paternal age does affect progeny outcome. These models provide several major advantages including the possibility to assess multi- transgenerational effects of paternal age on progeny in a relatively short time window. We then present the clinical observations relating advanced paternal age to fertility and effects on offspring with respect to perinatal health, cancer risk, genetic diseases, and neurodevelopmental effects. An overview of the potential mechanism operating in altering germ cells in advanced age is presented. This is followed by an analysis of the current state of management of reproductive risks associated with advanced paternal age. The numerous challenges associated with developing effective, practical strategies to mitigate the impact of advanced paternal age are outlined along with an approach on how to move forward with this important clinical quandary.
... There is an age-related increases in ROS, the so-called "free radical theory of aging", that is also evident in context of spermatogenesis and sperm quality (33)(34)(35). In fact, aging has been associated with reduce genetic quality in spermatogenic cells and sperm (36)(37)(38). Because NAD and NADP are required for both, maintaining a sufficient pool of the active antioxidant glutathione GSH, and for the enzymatic activity of PARP1, an important DNA repair factor, lower testicular NAD could potentially contribute to the aging-related accumulation of ROS and decline in sperm quality. ...
Article
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Advanced paternal age has increasingly been recognized as a risk factor for male fertility and progeny health. While underlying causes are not well understood, aging is associated with a continuous decline of blood and tissue NAD+ levels, as well as a decline of testicular functions. The important basic question to what extent ageing-related NAD+ decline is functionally linked to decreased male fertility has been difficult to address due to the pleiotropic effects of aging, and the lack of a suitable animal model in which NAD+ levels can be lowered experimentally in chronologically young adult males. We therefore developed a transgenic mouse model of acquired niacin dependency (ANDY), in which NAD+ levels can be experimentally lowered using a niacin-deficient, chemically defined diet. Using ANDY mice, this report demonstrates for the first time that decreasing body-wide NAD+ levels in young adult mice, including in the testes, to levels that match or exceed the natural NAD+ decline observed in old mice, results in the disruption of spermatogenesis with small testis sizes and reduced sperm counts. ANDY mice are dependent on dietary vitamin B3 (niacin) for NAD+ synthesis, similar to humans. NAD+-deficiency the animals develop on a niacin-free diet is reversed by niacin supplementation. Providing niacin to NAD+-depleted ANDY mice fully rescued spermatogenesis and restored normal testis weight in the animals. The results suggest that NAD+ is important for proper spermatogenesis and that its declining levels during aging are functionally linked to declining spermatogenesis and male fertility. Functions of NAD+ in retinoic acid synthesis, which is an essential testicular signaling pathway regulating spermatogonial proliferation and differentiation, may offer a plausible mechanism for the hypospermatogenesis observed in NAD+-deficient mice.
... During spermatogenesis, there is an increased demand of cysteine for the replacement of histones to protamines and to counteract the agerelated increase in local reactive oxygen species which leads to oxidative damage to testis (Conrad et al., 2015). Male spermatogonial stem cells isolated from tubules of old age mice (oxidatively damaged Sertoli cell microenvironment) colonize and propagate at higher efficiency when transplanted into young recipient males (no oxidative damage) indicating that microenvironment plays critical roles in ultimately determining male gamete quality (Oatley and Brinster, 2012;Paul and Robaire, 2013;Shinohara et al., 2003). Thus, SLC7A11-mediated cysteine/GSH redox balance in Sertoli cells could be one mechanism that creates an optimal microenvironment that protects germ cells from oxidative damage. ...
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Luteinizing hormone (LH) stimulates testosterone production from Leydig cells. Both LH and testosterone play important roles in spermatogenesis and male fertility. To identify LH - and testosterone - responsive transporter genes that play key roles in spermatogenesis, we performed large-scale gene expression analyses on testes obtained from adult control and Lhb knockout mice. We found a significant reduction in cystine/glutamate transporter encoding Slc7a11 mRNA in testes of Lhb null mice. We observed that Slc7a11/SLC7A11 expression was initiated pre-pubertally and developmentally regulated in mouse testis. Immunolocalization studies confirmed that SLC7A11 was mostly expressed in Sertoli cells in testes of control and germ cell-deficient mice. Western blot analyses indicated that SLC7A11 was significantly reduced in testes of mutant mice lacking either LH or androgen receptor selectively in Sertoli cells. Genetic and pharmacological rescue of Lhb knockout mice restored the testicular expression of Slc7a11 comparable to that observed in controls. Additionally, Slc7a11 mRNA was significantly suppressed upon Sertoli cell/testicular damage induced in mice by cadmium treatment. Knockdown of Slc7a11 in vitro in TM4 Sertoli cells or treatment of mice with sulfasalazine, a SLC7A11 inhibitor caused a significant reduction in intracellular cysteine and glutathione levels but glutamate content remained unchanged as determined by metabolomic analysis. Knockdown of Slc7a11 resulted in compensatory upregulation of other glutamate transporters belonging to the Slc1a family presumably to maintain intracellular glutamate levels. Collectively, our studies identified that SLC7A11 is an LH/testosterone-regulated transporter that is required for cysteine/glutathione but not glutamate homeostasis in mouse Sertoli cells.
... Not only PAE mutations causing early-onset diseases (e.g., RASopathies or skeletal dysplasias) have been described to increase with paternal age (for reviews, see Calabrese 2009, 2016;Goriely et al. 2009;Goriely and Wilkie 2012). Reports have also documented an increased frequency with paternal age of late-onset disorders, like breast cancer or cancers in the nervous system or of neurological and behavioral disorders, including autism (Hultman et al. 2011;Kong et al. 2012;Frans et al. 2013), bipolar disorders (Frans et al. 2008;Grigoroiu-Serbanescu et al. 2012), or schizophrenia (Svensson et al. 2012; for review, see Paul and Robaire 2013;Sharma et al. 2015;Acuna-Hidalgo et al. 2016). Thus, the observed PAE with consequences in neurological, heart, or cancer development might also be partially the result of DNMs in driver genes that lead to abnormalities in the signaling pathway (e.g., RTK-RAS). ...
Article
De novo mutations (DNMs) are important players in heritable diseases and evolution. Of particular interest are highly recurrent DNMs associated with congenital disorders that have been described as selfish mutations expanding in the male germline, thus becoming more frequent with age. Here, we have adapted duplex sequencing (DS), an ultradeep sequencing method that renders sequence information on both DNA strands; thus, one mutation can be reliably called in millions of sequenced bases. With DS, we examined ∼4.5 kb of the FGFR3 coding region in sperm DNA from older and younger donors. We identified sites with variant allele frequencies (VAFs) of 10 ⁻⁴ to 10 ⁻⁵ , with an overall mutation frequency of the region of ∼6 × 10 ⁻⁷ . Some of the substitutions are recurrent and are found at a higher VAF in older donors than in younger ones or are found exclusively in older donors. Also, older donors harbor more mutations associated with congenital disorders. Other mutations are present in both age groups, suggesting that these might result from a different mechanism (e.g., postzygotic mosaicism). We also observe that independent of age, the frequency and deleteriousness of the mutational spectra are more similar to COSMIC than to gnomAD variants. Our approach is an important strategy to identify mutations that could be associated with a gain of function of the receptor tyrosine kinase activity, with unexplored consequences in a society with delayed fatherhood.
... There is increasing evidence that aging of the human testis results in impairment of the two testicular main functions: steroidogenesis and spermatogenesis. More specifically, it has been observed that testicular aging leads to reduced levels of testosterone, a hormone essential for spermatogenesis [3], to an increase of de novo mutations in germ cells [4], alterations in sperm DNA methylation [5] and to lower gamete quality [6,7]. Additionally, there is evidence for structural alterations such as enlargement and sclerosis of the peritubular wall [8][9][10]. ...
Article
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Aging of human testis and associated cellular changes is difficult to assess. Therefore, we used a translational, non-human primate model to get insights into underlying cellular and biochemical processes. Using proteomics and immunohistochemistry, we analyzed testicular tissue of young (age 2 to 3) and old (age 10 to 12) common marmosets (Callithrix Jacchus). Using a mass spectrometry-based proteomics approach, we identified 63,124 peptides, which could be assigned to 5924 proteins. Among them, we found proteins specific for germ cells and somatic cells, such as Leydig and Sertoli cells. Quantitative analysis showed 31 differentially abundant proteins, of which 29 proteins were more abundant in older animals. An increased abundance of anti-proliferative proteins, among them CDKN2A, indicate reduced cell proliferation in old testes. Additionally, an increased abundance of several small leucine rich repeat proteoglycans and other extracellular matrix proteins was observed, which may be related to impaired cell migration and fibrotic events. Furthermore, an increased abundance of proteins with inhibitory roles in smooth muscle cell contraction like CNN1 indicates functional alterations in testicular peritubular cells and may mirror a reduced capacity of these cells to contract in old testes.
... ROS also target sterols and polyunsaturated lipid molecules in the sperm membrane. This lipid peroxidation results in the formation of various cytotoxic byproducts and importantly interferes with the normal fluidity of sperm membranes, which in necessary for sperm motility, sperm capacitation and ultimately sperm-egg fusion [39][40][41][42]. All those consequences of excessive ROS exposure ultimately contribute to the reduced fertility of older men. ...
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Similar to female reproductive health, male reproductive health declines with increasing age, albeit in a more gradual way. In the US, the average age of first-time fathers has been steadily increasing since 1980. This is concerning because increasing paternal age is positively correlated with reduced sperm chromatin quality and higher numbers of DNA strand breaks (DNA sb), which negatively affects pregnancy outcome and child development. While underlying reasons are not well understood, one of the well-known hallmarks of aging is a significant decline of body nicotinamide adenine dinucleotide (NAD) levels. We propose that low body-wide NAD levels provide a plausible explanation for metabolic alterations that are associated with declining hormonal production and testicular volume, as well as reduced sperm quality in aging men.
Article
The disease burden of de novo mutations (DNMs) has been evidenced only recently when the common application of next‐generation sequencing technologies enabled their reliable and affordable detection through family‐based clinical exome or genome sequencing. Implementation of exome sequencing into prenatal diagnostics revealed that up to 63% of pathogenic or likely pathogenic variants associated with fetal structural anomalies are apparently de novo, primarily for autosomal dominant disorders. Apparent DNMs have been considered to primarily occur as germline or zygotic events, with consequently negligible recurrence risks. However, there is now evidence that a considerable proportion of them are in fact inherited from a parent mosaic for the variant. Here, we review the burden of DNMs in prenatal diagnostics and the influence of parental mosaicism on the interpretation of apparent DNMs and discuss the challenges with detecting and quantifying parental mosaicism and its effect on recurrence risk. We also describe new bioinformatic and technological tools developed to assess mosaicism and discuss how they improve the accuracy of reproductive risk counseling when parental mosaicism is detected. This article is protected by copyright. All rights reserved.
Article
Accumulation of oxidative stress, DNA damage and impaired DNA repair appear to play critical roles in the decline of testicular function with aging. However, when those factors begin to lose control in testis during aging has not yet been well understood. This study was designed to assess the changes of oxidative stress and DNA damage status, and DNA repair capacity in testis during aging. Thus, male Sprague-Dawley rats at 3, 9, 15 and 24 months of age were used to delineate the dynamic changes in testicular weight and index, testosterone concentration, testicular histology, Nrf2-mediated oxidative stress, DNA damage, DNA repair and apoptosis. Results showed that testicular weight and index, testosterone concentration and spermatid number progressively declined from 9 to 24 months of age. Similarly, seminiferous tubule diameters and seminiferous epithelium heights gradually diminished with aging. Nrf2-mediated antioxidant defense ability was significantly impaired in testis with increasing age including decreased the activity of SOD and the expression levels of Nrf2, HO-1 and NQO-1, and increased the contents of MDA. In addition, DNA damage including DNA single-strand breaks (SSBs) and DNA double-strand breaks (DSBs) also progressively increased accompanied by increased levels of 8-hydroxydeoxyguanosine (8-OHdG) and γ-H2AX, and activated ATM/Chk2 and ATR/Chk1 pathway. Consistent with the results of Nrf2 pathway, the expression levels of APE1, OGG1 and XRCC1 involved in base excision DNA repair (BER) pathway increased from 3 to 9 months of age, and then gradually decreased after 9 months of age. Finally, TUNEL and Western blot results further confirmed germ cell apoptosis progressively increased from 3 to 24 months of age as evidenced by decreased ratio of Bcl-2/Bax and levels of Bcl-2 expression, and increased Bax expression levels. Taken together, our results suggest that downregulation of antioxidant ability mediated by Nrf2 pathway and impairment of BER capacity might correlate with increased DNA damage, and then induce declining testicular function during aging after adult.
Preprint
Full-text available
De novo mutations (DNMs) are an important player in heritable diseases and evolution, yet little is known about the different mutagenic processes in our germline given the difficulty to reliably identify ultra-low frequency variants. Of particular interest are highly recurrent DNMs associated with congenital disorders that have been described as selfish mutations expanding in the male germline, thus becoming more frequent with age. Here, we have adapted duplex sequencing (DS), an ultra-deep sequencing method that renders sequence information on both DNA strands; thus, one mutation can be reliably called in millions of sequenced bases. With DS, we examined ~4.5 kb of the FGFR3 coding region in sperm DNA from older and younger donors. We identified highly mutable sites with mutation frequencies 4-5 orders of magnitude higher than the genome average. Multiple mutations were found at a higher frequency, or exclusively, in older donors, suggesting that these mutations are testis exclusive mosaics expanding in the male germline with age. Also, older donors harbored more mutations associated with congenital disorders. Some mutations were found in both age groups with no significant difference, suggesting that these might result from a different mechanism (e.g., post-zygotic mosaicism). We also observed that independently of age, the frequency and deleteriousness of the mutations in sperm were elevated compared to reports in the population. Our approach is an important strategy to identify mutations that could be associated with aberrant receptor tyrosine kinase activity, with unexplored consequences in a society with delayed fatherhood.
Chapter
Ageing in evolutionary perspective delves into an area of inquiry that is still in development but that it promises to be of great utility in the study of ageing. In this chapter we analyse several evolutionary aspects of longevity and ageing and aim to lay down the foundations for an evolutionary gerontology.
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Although delaying fatherhood has become somewhat more popular, the heritable sequelae of this practice are not well understood. Advancing paternal age has, however, been implicated in numerous abnormal reproductive and genetic outcomes, including poorer semen quality, reduced fertility, and more frequent spontaneous abortions, as well as some 20 autosomal-dominant diseases such as Apert syndrome and achondroplasia. The investigators examined the effects of advancing male age on multiple genomic defects in sperm (reflected in the DNA fragmentation index [DFI]), chromatin integrity, gene mutations, and numeric chromosomal abnormalities. Participants were 97 men ranging in age from 22 to 80 years who were in good to excellent health and did not smoke. They were predominantly a white and highly educated population. Semen specimens were obtained after an average of 5 days without sexual activity. Age correlated positively with all 5 DFI end points analyzed. Thirty men, nearly one third of those studied, had percent DFI values at or above those previously associated with an increased risk of male infertility. After adjusting for age and abstinence, the frequency of sperm with high DNA stainability did not correlate with DFI end points. Age did correlate with fibroblast growth factor receptor 3 gene (FGFR3) mutations associated with achondroplasia. No associations were noted between age and the frequency of sperm with immature chromatin, aneuploidies or diploidies, or FGFR2 mutations (as in Apert syndrome). There also were no consistent correlations among genomic and semen quality end points except for an association between DFI and sperm motility. Male age did not correlate with the sperm sex ratio. Men who choose to delay fatherhood may be less likely to experience a successful pregnancy. Unlike older women, however, older men do not seem to be at increased risk of trisomic or triploid pregnancies. Semen quality does not reflect the presence of genomic damage to sperm. A small number of older men do appear to be at increased risk of transmitting multiple genetic and chromosomal defects.
Article
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Mutations generate sequence diversity and provide a substrate for selection. The rate of de novo mutations is therefore of major importance to evolution. Here we conduct a study of genome-wide mutation rates by sequencing the entire genomes of 78 Icelandic parent-offspring trios at high coverage. We show that in our samples, with an average father's age of 29.7, the average de novo mutation rate is 1.20 × 10(-8) per nucleotide per generation. Most notably, the diversity in mutation rate of single nucleotide polymorphisms is dominated by the age of the father at conception of the child. The effect is an increase of about two mutations per year. An exponential model estimates paternal mutations doubling every 16.5 years. After accounting for random Poisson variation, father's age is estimated to explain nearly all of the remaining variation in the de novo mutation counts. These observations shed light on the importance of the father's age on the risk of diseases such as schizophrenia and autism.
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The offspring of older fathers have an increased risk of neurodevelopmental disorders, such as schizophrenia and autism. In light of the evidence implicating copy number variants (CNVs) with schizophrenia and autism, we used a mouse model to explore the hypothesis that the offspring of older males have an increased risk of de novo CNVs. C57BL/6J sires that were 3- and 12-16-months old were mated with 3-month-old dams to create control offspring and offspring of old sires, respectively. Applying genome-wide microarray screening technology, 7 distinct CNVs were identified in a set of 12 offspring and their parents. Competitive quantitative PCR confirmed these CNVs in the original set and also established their frequency in an independent set of 77 offspring and their parents. On the basis of the combined samples, six de novo CNVs were detected in the offspring of older sires, whereas none were detected in the control group. Two of the CNVs were associated with behavioral and/or neuroanatomical phenotypic features. One of the de novo CNVs involved Auts2 (autism susceptibility candidate 2), and other CNVs included genes linked to schizophrenia, autism and brain development. This is the first experimental demonstration that the offspring of older males have an increased risk of de novo CNVs. Our results support the hypothesis that the offspring of older fathers have an increased risk of neurodevelopmental disorders such as schizophrenia and autism by generation of de novo CNVs in the male germline.
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Telomeres are repeating DNA sequences at the ends of chromosomes that protect and buffer genes from nucleotide loss as cells divide. Telomere length (TL) shortens with age in most proliferating tissues, limiting cell division and thereby contributing to senescence. However, TL increases with age in sperm, and, correspondingly, offspring of older fathers inherit longer telomeres. Using data and samples from a longitudinal study from the Philippines, we first replicate the finding that paternal age at birth is associated with longer TL in offspring (n = 2,023, P = 1.84 × 10(-6)). We then show that this association of paternal age with offspring TL is cumulative across multiple generations: in this sample, grandchildren of older paternal grandfathers at the birth of fathers have longer telomeres (n = 234, P = 0.038), independent of, and additive to, the association of their father's age at birth with TL. The lengthening of telomeres predicted by each year that the father's or grandfather's reproduction are delayed is equal to the yearly shortening of TL seen in middle-age to elderly women in this sample, pointing to potentially important impacts on health and the pace of senescent decline in tissues and systems that are cell-replication dependent. This finding suggests a mechanism by which humans could extend late-life function as average age at reproduction is delayed within a lineage.
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This report presents 2009 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal characteristics including age, live-birth order, race and Hispanic origin, marital status, hypertension during pregnancy, attendant at birth, method of delivery, and infant characteristics (period of gestation, birthweight, and plurality). Birth and fertility rates by age, live-birth order, race and Hispanic origin, and marital status also are presented. Selected data by mother's state of residence are shown, as well as birth rates by age and race of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Descriptive tabulations of data reported on the birth certificates of the 4.13 million births that occurred in 2009 are presented. Denominators for population-based rates are postcensal estimates derived from the U.S. 2000 census. The number of births declined to 4,130,665 in 2009, 3 percent less than in 2008. The general fertility rate declined 3 percent to 66.7 per 1,000 women aged 15-44 years. The teenage birth rate fell 6 percent to 39.1 per 1,000. Birth rates for women in each 5-year age group from 20 through 39 years declined, but the rate for women 40-44 years continued to rise. The total fertility rate (estimated number of births over a woman's lifetime) was down 4 percent to 2,007.0 per 1,000 women. The number and rate of births to unmarried women declined, whereas the percentage of nonmarital births increased slightly to 41.0. The cesarean delivery rate rose again, to 32.9 percent. The preterm birth rate declined to 12.18 percent; the low birthweight rate was stable at 8.16 percent. The twin birth rate increased to 33.2 per 1,000; the triplet and higher-order multiple birth rate rose 4 percent to 153.5 per 100,000.
Article
Apert syndrome was studied to determine birth prevalence, mutation rate, sex ratio, parents' age, and ethnicity among 2,493,331 live births registered in the California Birth Defects Monitoring Program (CBDMP) from 1983 through 1993; 31 affected infants were identified. The sample was completed with an additional 22 cases from the Center for Craniofacial Anomalies (CCA), University of California, San Francisco, for a total of 53 affected children. Birth prevalence, calculated from the CBDMP subsample, was 12.4 cases per million live births (confidence interval [CI] 8.6,17.9). The calculated mutation rate was 6.2 × 10−6 per gene per generation. Asians had the highest prevalence (22.3 per million live births; CI 7.1,61.3) and Hispanics the lowest (7.6 per million, CI 3.3-16.4). In the large population-based CBDMP subsample, there was an almost equal number of affected males and females, (sex ratio 0.94) but in the clinical CCA subsample, there were more affected females (sex ratio 0.79). For all cases, the mean age of mothers was 28.9±6.0 years, and of fathers was 34.1±6.2 years. Almost half of fathers were older than 35 years when the child was born; for more than 20% of cases, both parents were older than 35 years. These findings may support the view that point mutations appear to be more commonly associated with paternal than with maternal alleles. Representing the largest systematically ascertained population-based study of Apert syndrome to date, they provide a reliable basis for genetic counseling and decision-making, and for focused research to define the cause of this syndrome. Am. J. Med. Genet. 72:394–398, 1997. © 1997 Wiley-Liss, Inc.