Journal of Genetic Counseling [jgc] ph105-jogc-368835 February 27, 2002 9:56 Style ﬁle version Nov. 19th, 1999
Journal of Genetic Counseling, Vol. 11, No. 2, April 2002 (
Genetic Counseling and Screening of Consanguineous
Couples and Their Offspring: Recommendations
of the National Society of Genetic Counselors
Robin L. Bennett,
Arno G. Motulsky,
Debra Lochner Doyle,
C. Ronald Scott,
The objective of this document is to provide recommendations for genetic coun-
seling and screening for consanguineous couples (related as second cousins or
closer) and their offspring with the goals of
1. providing preconception reproductive options,
2. improving pregnancy outcome and identifying reproductive choices,
3. reducing morbidity and mortality in the 1st years of life, and
4. respecting psychosocial and multicultural issues.
Department of Medicine, Division of Medical Genetics, University of Washington, Seattle,
Department of Genetics, Division of Medical Genetics, University of Washington, Seattle,
Centre for Human Genetics, Edith Cowan University, Perth, Australia.
Department of Pediatrics, Division of Medical Genetics, Stanford University, Stanford, California.
Department of Obstetrics and Gynecology, Division of Medical Genetics, University of Washington,
Genetic Services Section, Washington State Department of Health, Seattle, Washington.
Paciﬁc Northwest Regional Genetics Group, Child Development and Rehabilitation Center, Oregon
Health Sciences University, Eugene, Oregon.
Department of Pediatrics, University of Washington, Seattle, Washington.
Department of Medical Genetics, Children’s and Women’s Health Centre of British Columbia,
Vancouver, British Columbia, Canada.
Departments of Pediatrics and Molecular and Medical Genetics, Child Development and Rehabili-
tation Center, Doernbecher Children’s Hospital, Oregon Health & Science University, Portland,
Correspondence should be directed to Robin L. Bennett, MS, CGC, Division of Medical
Genetics,UniversityofWashington, Box357720, Seattle,Washington98195-7720; e-mail:robinb@
2002 National Society of Genetic Counselors, Inc.
Journal of Genetic Counseling [jgc] ph105-jogc-368835 February 27, 2002 9:56 Style ﬁle version Nov. 19th, 1999
98 Bennett et al.
The recommendations are the opinions of a multicenter working group (the Con-
sanguinity Working Group (CWG)) with expertise in genetic counseling, medical
public health genetics, which was convened by the National Society of Genetic
Counselors (NSGC). The consensus of the CWG and NSGC reviewers is that be-
yond a thorough medical family history with follow-up of signiﬁcant ﬁndings, no
additional preconception screening is recommended for consanguineous couples.
Consanguineous couples should be offered similar genetic screening as suggested
for any couple of their ethnic group. During pregnancy, consanguineous couples
ultrasonography. Newborns should be screened for impaired hearing and detec-
tion of treatable inborn errors of metabolism. These recommendations should not
be construedas dictating an exclusive courseof management,nor does use of such
recommendations guarantee a particular outcome. The professional judgment of
a health care provider, familiar with the facts and circumstancesof a speciﬁc case,
will always supersede these recommendations.
KEYWORDS: consanguinity;geneticcounseling;geneticscreening; genetictesting;incest;newborn
screening; tandem mass spectrometry.
First let me start by saying that I have lived with my ﬁrst cousin for six years and we are
madly in love. About four years ago I became pregnant. We had never discussed having
children before, mainly because of the “taboo” of us being together in the ﬁrst place. I
immediately went to my gynecologist and explained the situation. He was a bit stunned
and said that in all his years of practice he had never come across anything like this. The
only thing he told me was that our baby would be sick all the time and then suggested that
I have an abortion. Me? Have an abortion? I was heartbroken. He told me that he would
check into it more and call me back later. That night I got a call from his receptionist who
told me that it was illegal for us to be married, but it was legal for us to have the baby.
We were so confused. I went to the library and searched for information, with no luck. My
cousin told his mom, who went nuts, saying that our baby would be retarded. I went ahead
with the abortion. If my doctor suggested it, I thought it was the right thing to do at the
time—the worst mistake of my life. About a year later I ﬂipped on the TV and Jenny Jones
was doing a show on cousin couples, saying that cousin couples only have a 3% higher
chance of something being wrong with the baby than that of “normal” couples. Needless
to say I cried and cried. If only I had seen this show a year sooner or my doctor would have
known the facts.
—Anonymous participant, on-line support group for cousin romances, August 2000
Theneed todisseminate recommendationsfor genetic counselingand screen-
ing for consanguineous unions is dramatically illustrated in the preceding quote.
There is limited published information about how to advise and screen consan-
guineous couples, their pregnancies, and their offspring (Baird and McGillivray,
1982;Bennettetal.,1999;Hall,1978;Harper, 1998). A1996surveyofmedical ge-
neticistsand geneticcounselorsin theUnitedStates foundwide variationin the ge-
netic screening practices provided to consanguineous couples and their offspring,
as well as disparity in risk ﬁgures quoted to these couples (Bennett et al., 1999).
Consanguineous couples, their pregnancies, and their offspring are evaluated
Journal of Genetic Counseling [jgc] ph105-jogc-368835 February 27, 2002 9:56 Style ﬁle version Nov. 19th, 1999
Consanguinity: Genetic Counseling and Screening 99
preconception or prenatal genetic counseling services. The child of an incestuous
union may come to medical attention if the child is to be placed in foster care
or adopted, or if the incestuous relationship is identiﬁed during pregnancy. The
following recommendations focus on genetic screening and testing, and genetic
counseling for these indications.
The termsinbreedingand consanguinity are used interchangeably to describe
unions between couples who share at least one common ancestor. Inbreeding in
population genetic terms refers to a departure from nonrandom “mating” in that
individuals “mate” with those more similar (genetically) to them than if they
“mated at random” in the population. Inbreeding is a pejorativeterm when applied
Although marriages between close relatives are discouraged (or even illegal)
in North America, in many cultures (particularly in the Middle East, Asia, and
Africa) preferred marriages are between ﬁrst cousins, or less commonly, between
an uncle and niece or between double ﬁrst cousins (Bittles, 1998; Harper, 1998).
Double ﬁrst cousins are the offspring of two sets of siblings, such as two brothers
married to two sisters (Fig. 1 example B). In some parts of the world 20–60%
of all marriages are between close biological relatives (Bittles, 1998). Reviews of
Roman Catholic marriage dispensations in the United States and Canada found
the prevalence of requests for cousin marriages to be between 1.3–1.5% and 0.1–
1968; Lebel, 1983). A study of cousin marriages in Wisconsin from 1843 to 1981
suggests a rate of consanguineous marriage of about 1 in 1300 marriages (Lebel,
1983). There are speciﬁc communities within theUnited States and Canada where
consanguineous unions are common (Table I) (Bear et al., 1988; Bittles, 1998;
Brown, 1951; De Braekeleer and Ross, 1991; Drosten et al., 1999; Freire-Maia,
1968; Moore, 1987; Thomas et al., 1987).
Thetermincestisdeﬁneddifferentlyinbiological and legalsettings.Thelegal
deﬁnition often includes unions between nonbiological relatives (e.g., between
stepfather and stepdaughter, or step siblings). The prevalence of incest in the
United States and Canada is difﬁcult to establish, and is likely to be underreported
because of the associated social stigma and legal consequences. Data on incest is
mostly gathered from retrospective studies of child sexual abuse; approximately
half of this abuse is estimated to be by family members (which may include
nonbiological relatives) (Whetsell-Mitchell, 1995). Sibling–sibling contact may
be the most common form of incestuous activity (Maddock and Larson, 1995).
Incest perpetrators are found across all socioeconomic and ethnic backgrounds. In
this report, incest is deﬁned as a mating between biological ﬁrst-degree relatives
(i.e., father–daughter, mother–son, brother–sister). There is no published data on
100 Bennett et al.
Fig. 1. Examples of consanguineous unions and their coefﬁcients of inbreeding.
the number of offspringproduced from incestuous unions betweenbiological ﬁrst-
The offspring of consanguineous unions may be at increased risk for genetic
disorders because of the expression of autosomal recessive gene mutations in-
herited from a common ancestor. The closer the biological relationship between
parents, the greater is the probability that their offspring will inherit identical
copies of one or more detrimental recessive genes. For example, ﬁrst cousins are
predicted to share 12.5% (1/8) of their genes. Thus, on average, their progeny
will be homozygous (or more precisely, autozygous) at 6.25% (1/16) of gene loci
(i.e., they will have received identical gene copies from each parent at these sites
in their genome).
Offspring of consanguineous unions may also be at increased risk for disor-
ders of multifactorial or complex inheritance. However, well-controlled studies
Consanguinity: Genetic Counseling and Screening 101
Table I. Examples of Data on Consanguineous Marriage in Select Populations in the United States
Collection Study Sample Consanguinity coefﬁcient
Location period population size (%) (α) Reference
New Brunswick 1959 RC
dispensation 686 4.8 0.0010 Freire-Maia
Bathurst, Canada (1968)
Quebec 1959 RC dispensation 600 6.0 0.0012 Freire-Maia
Gaspe, Canada (1968)
Kentucky, 1942 Household 107 18.7 0.0061 Brown
(Beech Creek), survey (1951)
New Mexico, 1959 RC dispensation 370 1.4 0.0004 Freire-Maia
(Gallup), USA (1968)
Austin, Texas, 1959 RC dispensation 675 1.3 0.0006 Freire-Maia
Kansas, 1980 Pedigree 194 33.0 0.0030 Moore
(Mennonites), analysis (1987)
Boston, 1980s Pedigree 21 61.9 0.0170 Thomas
(“Gypsies”), analysis et al.
Utah (Mormon), 2000 Utah population 303,675 1.2 0.0004 Jorde
USA database (2001)
Adapted from Bittles (1998).
RC = Roman Catholic.
evaluating the effect of consanguinity on multifactorial diseases of childhood
and adulthood have not been conducted. The studies to date are not conclu-
sive as to whether consanguinity increases the risk for multifactorial disorders
(Bittles, 1998, 2001; Jaber et al., 1997; Shami et al., 1991; Stoltenberg et al.,
The coefﬁcient of inbreeding (F) providesa numerical estimate of the degree
of inbreeding of an individual. F values are higher for unions between closer rela-
tives,that is,the offspringof anincestuous relationship havea greater F valuethan
do those of a ﬁrst-cousin relationship. The F valuesfor various degreesof consan-
guineous relationships are shown in Fig. 1. The mean inbreeding coefﬁcient (α)
can also be calculated for entire populations in which a proportion of marriages
are consanguineous, and for individuals who are related through multiple loops of
consanguinity (see under Populations With High Mean Coefﬁcients of Inbreeding
and under Pedigrees With Multiple Loops of Consanguinity). Populations with
a high mean inbreeding coefﬁcient do not necessarily represent a community of
close cousin marriages, and in fact cousin marriage may be discouraged (Jorde,
Few studies document the actual risks to the offspring of consanguineous
unions. The risks quoted for birth defects and mental retardation are often based
102 Bennett et al.
onstudies of non-Western populationswhereconsanguineous unions arecommon,
and they may not be applicable to consanguineous unions in the United States and
Canada (Al-Abdulkareem and Balal, 1998;Al-Awadiet al., 1985;Al-Gazali et al.,
1997;Bittles,1998,2001;Bittlesetal.,1991; Bittles andNeel,1994;Harper,1998;
Jaber et al., 1997, 1998; Kaku and Freire-Maia, 1992; Madhaven and Narayan,
1991; Schull and Neel, 1965; Shami et al., 1991; Vogel and Motulsky, 1996).
Furthermore, in all such studies, the criteria for what is considered a signiﬁcant
medical problem in offspring are not standardized. Studies using excess mortality
to measure the adverse effects ofinbreeding often did not account for the effects of
sociodemographic variables such as maternal age, birth interval, socioeconomic
status, and maternal education, thereby exaggerating the adverse effect of consan-
guinity (Bittles, 1998; Kaku and Freire-Maia, 1992). The risk of adverse medical
outcomes for the offspring of consanguineous unions, as compared to a baseline
riskforthegeneralpopulation,isreviewedunderBaselineRiskfor the Offspringof
Consanguineous Unions Compared to Those From Nonconsanguineous Unions.
These recommendations are intended to assist health care professionals who
provide genetic counseling and screening to consanguineous couples and their
offspring. The recommendations focus on the offspring of cousin unions (related
as biologic second cousins or closer), and the offspring of incestuous unions
(relationships between biologic ﬁrst-degree relatives). The recommendations con-
sider genetic screening and testing that is available to practitioners in the United
States and Canada, given current standards of health care prevention and genetic
screening offered to the general (nonconsanguineous) population. Psychosocial
and multicultural issues in genetic counseling are reviewed.
The goals of these recommendations are to
A. Providerisk assessment and reproductiveoptions to consanguineous cou-
ples who request genetic counseling in a preconception setting.
B. Improve pregnancy outcome and provide reproductive options when
parental consanguinity is identiﬁed in a pregnancy.
C. Reduce morbidity and mortality in the ﬁrst years of life for children from
D. Consider psychosocial and multicultural issues related to genetic coun-
seling for consanguineous couples, with a focus on nonincestuous rela-
These recommendations do not address the legal ramiﬁcations of consan-
guineous unions, which are unique to each state in the United States. Although
Consanguinity: Genetic Counseling and Screening 103
the medical and genetic consequences of biological incest are reviewed in these
recommendations, the psychosocial considerations are very different from those
of cousin unions. For example, there is a major attitudinal difference regarding
a union involving consenting adult cousins as compared to incestuous abuse of a
minor. Unions between cousins are the primary focus of this paper.
The authoring subcommittee (Consanguinity Working Group (CWG)) con-
sisted of experts in genetic counseling (RLB, SU, DLD, KS, EC), medical genet-
ics (AGM, LH, CRS, EC, BM, RDS), public health genetics (DLD, KS, AGM),
genetic epidemiology (AB), biochemical genetics (CRS, RDS), pediatric genetics
Society of Genetic Counselors) members (AGM, LH, CRS, EC, BM, RDS, AB).
The MEDLINE and PubMed databases were searched (using the key words
consanguinity and incest) to locate relevant English language medical papers pub-
lished between 1965 and August 2000. Additional papers were identiﬁed through
bibliographies of articles. Papers were reviewed with attention to genetic counsel-
ing and multicultural issues. The data was reviewedand evaluated according to the
following categories outlined by the U.S. Preventive Services Task Force (1995):
I. Evidence obtained from at least one properly designed randomized controlled
II-1. Evidence obtained from well-designed controlled trials without randomiza-
II-2. Evidence obtained from well-designed cohort or case-control analytic
studies, preferably from more than one center or research group.
studies, or reports of expert committees.
of Categories I or II was identiﬁed.
The authoring committee sought expert review from specialists in North
America. Opinions were sought from representatives of a support group for con-
sanguineous couples (www.cousincouples.com). The recommendations were pre-
ican Society of Human Genetics. They also were presented in September 2000 at
the First International Workshop on Consanguinity, Endogamy and Cultural Di-
versity in Leeds, United Kingdom (www.consang.net/Leeds2000/index.htm). A
draft of the document was made available on the Internet to all members of the
NSGC for comment (91% of the 1867 NSGC members are registered on the
NSGC listserv). The NSGC membership includes genetic counselors, physicians,
nurses, attorneys, PhD genetics professionals, social workers, and students. The
104 Bennett et al.
NSGC Ethics Subcommittee (composed of seven genetic counselors, and an ad
hoc bioethicist/clergy representative) and an attorney for the NSGC reviewed the
revised document. No conﬂicts with the NSGC Code of Ethics were identiﬁed in
the ﬁnal document. The NSGC Board of Directors unanimously approvedthe ﬁnal
document in May 2001.
PRIMARY GENETIC SCREENING AND TESTING CONSIDERATIONS
FOR CONSANGUINEOUS COUPLES AND THEIR OFFSPRING
Baseline Risk for the Offspring of Consanguineous Unions Compared
to Those From Nonconsanguineous Unions
The probability of an adverse outcome in the offspring of a consanguineous
union is not an absolute number. Rather, the estimated risk must be based upon
background population risk, degree of consanguinity, and relevant family history.
The chance of a signiﬁcant medical problem in the offspring of a consanguineous
couple can be thought of as two additive risks—the background population risk,
plus the additional risk because of consanguinity. Population studies in the United
States and Canada that estimate the general population risk for birth defects in the
ﬁrst years of life are summarized in Table II (Applegarth et al., 2000; Baird et al.,
theoffspringof consanguineous unions is impossible because the populations from
which these risk estimates have been generated vary in their sociodemographic
characteristics, the methods of subject ascertainment, and the deﬁnition of an
adverse health outcome. For illustrative purposes, data from several studies that
estimate the excess risks of birth defects and prereproductive mortality in the
Table II. Examples of Studies Determining Baseline Population Estimates for Birth Defects, Genetic
Disorders, and Metabolic Disease in the United States and Canada
Reference Risks quoted Population studied
Baird et al. (1988) 5.3%, for disease with important
genetic component by age
British Columbia, Canada
Applegarth et al. (2000) 0.04% (40 cases per 100,000 live
births), minimum incidence of
British Columbia, Canada
Wilcox and Marks
(1999) (Center for
3–4%, for major birth defects in
1st year of life
USA, >17 million births from
Leppig et al. (1987) 3.16 %,for major malformationto
age 5 days
Boston, MA, USA, 4305
Diseases of amino acids, organic acids, urea cycle, galactosemia, lactic acidosis, glycogen storage
disease, lysosomal storage diseases, peroxisomal and mitochondrial respiratory chain dysfunction.
Consanguinity: Genetic Counseling and Screening 105
Table III. Estimate of Riskto theOffspring ofa FirstCousin Union Compared toNonconsanguineous
Population Risk, general Risk, offspring
Reference studied population of ﬁrst cousins
Jaber et al.
Compiled data from
9 populations (Chicago,
U.S., Middle East,
Demirel et al.
1120 randomly selected
(n = 20/2804)
(n = 13/543)
et al. (1999)
1.56 million births in
Norway from 1967 to
1.5% structural birth
defects in ﬁrst few
days of life
3.6% structural birth
defects in ﬁrst few
days of life
Data on 9122 pregnancies
in the citiesof Hiroshima
and Nagasaki, Japan
Mortality in childhood:
Compiled data from
38 populations in eastern
and southern Asia,
Middle East, Africa,
Europe, South America
median 10 years:
Jorde (2001) Compiled data on 303,675
members of the Utah
between 1847 and 1945
mortality (before age
3.3% if parents had child with a previous birth defect.
6.8% if parents had child with previous birth defect.
offspring of ﬁrst cousin unions are reviewed in Table III (Bittles and Neel, 1994;
Demirel et al., 1997; Jaber et al., 1998; Jorde, 2001; Schull and Neel, 1965;
Stoltenberg et al., 1999). In these studies, the increased risk for a signiﬁcant birth
of the general population risk. There is an estimated 4.4% risk for prereproductive
mortality (to median age of 10 years) above that of the background population
risk (this number includes birth defects resulting in mortality) (Bittles and Neel,
1994). This ﬁgure is derived from combined data from 38 populations in eastern
and southern Asia, Africa, Europe, and South America.
sanctions to incestuous unions, there is a paucity of data regarding adverse medi-
cal outcomes in the offspring of incestuous unions. Published studies are fraught
with signiﬁcant ascertainment biases. These biases, such as lack of paternity
documentation, young maternal age, possible parental disease and/or intellectual
impairment, parental socioeconomic status (or lack of report of this variable), and
complications of unsuccessful attempted pregnancy termination (Bittles, in press).
Table IV summarizes the four most comprehensive published studies of incest
(Adams and Neel, 1967; Baird and McGillivray, 1982; Carter, 1967; Seemanova,
106 Bennett et al.
Table IV. Abnormalities in the Offspring of First Degree Incestuous Unions
Year and origin Number of Years Known autosomal Congenital Nonspeciﬁc severe Mild intellectual
of study participants follow-up Normal recessive disorders malformations/SIDS
intellectual impairment impairment
USA (Adams and 18 0.5 7 2 4 0 5
UK (Carter, 1967) 13 4–6 5 2 1 1 4
Czechoslovakia 161 1–37 78 20 21 24 18
Canada (Baird and 21 0.5–1.9 8 1 8 0 4
Totals 213 98 (46.0%) 25 (11.7%) 34 (16.0%) 25 (11.7%) 31 (14.6%)
Adapted from Bittles (in press).
SIDS – sudden infant death syndrome.
Consanguinity: Genetic Counseling and Screening 107
1971). Three of these studies were retrospective, and the controls for matched
nonincestuous pregnancies were highly variable (Baird and McGillivray, 1982;
Carter, 1967; Seemanova, 1971). These studies are also limited in the number
of years that the incestuous progeny were followed. Although the highest risk
for morbidity and mortality would be expected in the ﬁrst year of life, moderate
medical problems and mental retardation would not be evident until later.
By combining the four sets of data in Table IV, and selecting the cases of
speciﬁc autosomal recessive disorders recorded (n = 25), plus major congenital
malformations (n = 34), and nonspeciﬁc severe intellectual handicap (n = 25),
84 of 213 (39.4%) of the progeny of incestuous unions had died or were im-
paired (Bittles, in press). This analysis does not control for nongenetic variables.
In the two studies for which nonconsanguineous reference groups were available,
8.0% of the control children (9 of 113) died or had a serious defect (Carter, 1967;
Seemanova, 1971). Thus, the excess level of death and severe defect in the off-
spring of incestuous unions (a proportion of which may have been nongenetic in
origin) was 31.4% (Bittles, in press).
An alternative method of analysis is to use the risks observed in ﬁrst cousin
unions to calculate mortality and morbidity associated with incest, based on the
coefﬁcient of inbreeding F (refer to Fig. 1). This assumes that risks for mortality
and birth defects are directly scalable with F, which may not be an accurate
assumption, particularly for disorders with complex inheritance. If the excess pre-
reproductive mortality rate among ﬁrst cousin offspring (who have an F value of
1/16) is 4.4%, then one would predict an excessdeath rateof approximately 17.6%
foroffspringofincestuousunions(withan F valueof1/4).Likewiseiftheoffspring
of ﬁrst cousin unions are estimated to be at 1.7–2.8% risk above the background
(Table III), then the predicted risk to the offspring of ﬁrst-degree relatives would
be at 6.8–11.2%risk abovethe populationbackground forsigniﬁcant birthdefects.
Genetic Screening and Testing for Consanguineous Couples
and Their Offspring
The simplest and most comprehensive tool for providing genetic screening
to consanguineous couples and their offspring is obtaining a medical family his-
tory covering 3–4 generations from the consultand(s), as reviewed under Medical
Family History (Bennett, 1999). Appropriate testing can be requested based on
the family history and the ethnic background, just as it would be offered in the
genetic evaluation of a nonconsanguineous couple. When a known or suspected
genetic condition is identiﬁed in a fetus or newborn of a consanguineous union,
the genetic evaluation should proceed as it would for a nonconsanguineous union.
Likewise,geneticevaluationandriskassessmentforaconsanguineous couple with
a previous child with a known or suspected genetic condition should proceed as
it would for a nonconsanguineous couple. Genetic evaluation of the offspring of a
108 Bennett et al.
consanguineousunion wouldproceedwith ahigh index of suspicionfor autosomal
recessive disorders in the differential diagnosis.
Endogamy refers toa society in which mating partners are preferentially cho-
sen from within the group, usually because of a combination of geographical,
cultural, and religious factors. In populations that are highly endogamous, genetic
counseling and screening should be offered with consideration of the genetic dis-
orders that occur with higher frequency in that speciﬁc population (because of
founder effects and genetic drift), as well as current standards of preconception,
prenatal, and newborn genetic screening for the general population in that geo-
graphic location (see under Baseline Risk for the Offspring of Consanguineous
Unions Compared to Those From Nonconsanguineous Unions). For example,
cystic ﬁbrosis carrier testing might be offered to a Northern European couple who
are ﬁrst cousins, because cystic ﬁbrosis is a common condition in that population
(Grody et al., 2001). A listing of over 1000 references to inherited disorders that
havebeendescribedinspeciﬁcpopulationgroups is availableatwww.consang.net.
Notethat the probabilitythatanoffspringofa consanguineous union,affectedwith
an autosomal recessive condition is autozygous is lower if the carrier frequency
(q) is high and the coefﬁcient of inbreeding (F) is low, than it would be for an
autosomal recessive disorder for which q is small (e.g., the offspring of a con-
sanguineous union can be an autosomal recessive condition without being autozy-
gous). Ten Kate et al. (1991) use the example of two children with cystic ﬁbrosis
born to a couple related through multiple loops of consanguinity where both chil-
dren were compound heterozygotes and had a delta F508 mutation and another
mutation. The anticipated result in a consanguineous union would be that both
parents carried the same mutant allele and children would be homozygous for the
same mutant allele.
Preconception Genetic Screening for Consanguineous Couples
counseling prior to marriage or before they conceive a pregnancy. Aside from a
thorough medical family history, there is no need to offer any genetic testing
on the basis of consanguinity alone. The couple may be from a population or
community that has a high coefﬁcient of inbreeding because of many common
ancestors (e.g., Amish community in the United States; Hutterites from Alberta
and Saskatchewan, Canada, etc.). Certain autosomal recessive disorders may be
common in a speciﬁc population and carrier screening can be an option in this
instance (refer to www.consang.net).
Genetic Screening for a Fetus of a Consanguineous Union
As in nonconsanguineous unions, maternal–fetal serum marker screening
should be offered at 15–18 weeks gestation to screen for congenital medical
Consanguinity: Genetic Counseling and Screening 109
conditions including neural tube defects (American College of Obstetrics and
Gynecology, August 1994). The use of ﬁrst trimester maternal–fetal markers
and ultrasound as an early mode of screening for some congenital anomalies
and chromosome aneuploidy is promising, but this method is still investigational
(Economides et al., 1999). The pregnancy of a consanguineous couple should
be screened for major fetal structural anomalies with the use of high-resolution
fetal ultrasound at 20–22 weeks gestation (Allan, 2000; Economides et al., 1999;
Schwarzleret al., 1999). The identiﬁcation of an anomaly by fetal ultrasound or an
abnormal maternal–fetal marker proﬁle should be evaluated without special con-
sideration to consanguinity (aside from considering autosomal recessive disorders
as a possible etiology). The chance of having a child with a chromosome anomaly
does not appear to be increased in consanguineous unions (Devoto et al., 1985;
Hamamy et al., 1990).
Genetic Screening for Offspring of Consanguineous Unions
The children of consanguineous unions are at increased risk for autosomal
recessive disorders, some of which may be inborn errors of metabolism with treat-
ment options (Applegarthet al., 2000; Rashed et al., 1995). In addition to standard
neonatal screening, the offspring of consanguineous unions (where the parents
are related as second cousins or closer) should be offered supplemental neonatal
screening of ﬁlter paper blood spots by tandem mass spectrometry (MS/MS) for
analysis of amino acids and acylcarnitines (American Society of Human Genetics
Social Issues Committee and the American College of Medical Genetics Social,
Ethical, and Legal Issues Committee, 2000; Rashed et al., 1995; U.S. Depart-
ment of Health and Human Services, April 13, 2001). Some states in the United
States and provinces in Canada already offer MS/MS screening for all neonates.
Infants with abnormal results should be offered diagnostic conﬁrmation and re-
ferral to medical specialists with expertise in inborn errors of metabolism (U.S.
Department of Health and Human Services, April 13, 2001).
Manyforms ofprelingual hearing lossare inherited in an autosomalrecessive
pattern and collectively represent one of the most common groups of recessively
inherited conditions (Willems, 2000). Early identiﬁcation of children with hearing
impairment, accompanied by treatment and appropriate learning opportunities,
is likely to improve their ability for successful communication strategies in a
hearing world. Therefore, hearing screening should be offered by 3 months of
age, and ideally before hospital discharge to children of consanguineous unions
(relatedassecond cousins orcloser).Universalnewbornhearingscreening is being
implemented in some U.S. states and Canadian Provinces (refer to the American
Speech–Language–Hearing Association website at www.asha.org).
In the United States and Canada the standard of care is for all children to re-
ceive periodic well child checkups with their primary health care providers (Com-
mittee on Practice and Ambulatory Medicine, American Academy of Pediatrics,
110 Bennett et al.
2000, website, www.AAP.org). These scheduled evaluations are particularly im-
portant for the child of a consanguineous union so that potential medical prob-
lems of genetic origin can be identiﬁed at an early age, allowing appropriate
PRIMARY GENETIC COUNSELING ISSUES IN CONSANGUINITY
Ascertain the client’s primary questions and concerns and mutually develop
a plan to address these concerns.
Medical Family History
A. The consanguineous relationship should be documented in the form of
a pedigree (Fig. 1). Patients often confuse degrees of relationships (e.g.,
confuse ﬁrst cousins once removed with second cousins, or confuse step-
relativesasbeingbiologicallyrelated)(Bennett, 1999; Spence and Hodge,
2000; Young, 1999).
i. Using standardized pedigree symbols (Bennett, 1999; Bennett et al.,
1995) obtain a comprehensive three or more generation pedigree from
the consultand or proband. Include offspring, siblings, parents, grand-
parents, aunts, uncles, nieces, nephews, and ﬁrst cousins of the con-
sultand or proband, as appropriate.
ii. Consanguinity is noted on the pedigree with two parallel mating lines
between the couple (Fig. 1) (Bennett, 1999; Bennett et al., 1995).
B. Note in particular if any relatives have a medical history compatible
with inborn errors of metabolism (Table V), or other potentially genetic
disorders (Bennett, 1999).
i. Verify potential genetic disorders with medical records, if possible.
Consider referral for clinical genetic evaluation of individual(s) sus-
pected to be affected with a genetic condition, as needed.
ii. Provide a genetic risk assessment for carrier status and the chances of
affected offspring if autosomal recessive disorders or other inherited
conditions are identiﬁed (Harper, 1998; Spence and Hodge, 2000;
Vogel and Motulsky, 1996; Young, 1999).
iii. Offer genetic testing depending on test availability, as appropriate.
C. Note the ethnicity of all grandparents and offer genetic screening appro-
priatefor any couple ofthatethnic background (e.g.,cysticﬁbrosistesting
for a Caucasian couple, hemoglobinopathy and thalassemia screening for
African American couples or those of Caribbean descent, thalassemia
screening for couples of Eastern Mediterranean or Asian background,
Consanguinity: Genetic Counseling and Screening 111
Table V. Speciﬁc Patient Interview Questions to Help Identify a Family History of Inborn Errors of
Do any of your biological relatives have a history of
• Mental retardation or developmental delay?
• Failure to thrive (e.g., poor weight gain, poor feeding, frequent vomiting)?
• Normal physical and/or mental development followed by progressive decline of physical
and/or mental skills?
• Floppiness (hypotonic or low muscle tone)?
• Chronic illness, infections, or vomiting? Note any triggers to illness, particularly fasting
or unusual dietary patterns
• Unusual odor, particularly when ill? Describe the odor
• Cataracts, corneal clouding, lens or retinal abnormalities, detected at or soon after birth or in
• A seizure disorder?
• Sudden infant death, particularly if preceded by a period of vomiting or fasting from an
• Death in the ﬁrst few days of life or in early childhood?
Adapted from Bennett (1999).
D. Maintain conﬁdentiality of the family history with respect to the consul-
tand(s) and extended family members.
Psychosocial History of the Consultand(s)
Attempt to build a relationship with the consultand(s) by validating feelings,
empathizing, and listening. For each consultand, assess and address
A. Level of comprehension and communication.
B. Level of education, employment, and social functioning.
C. Perceivedrisk and perceivedburden of risk. Clarify any family myths and
misconceptions about risks.
D. Coping skills.
E. Family/community support structure. Discuss any stigma that the consul-
tand(s) may perceive from family and peers.
F. Cultural beliefs about causation of birth defects and risks to offspring
associated with consanguinity.
A. Analyze the pedigree. Calculate the coefﬁcient of inbreeding if multiple
loops of consanguinity are present (see under Pedigrees With Multiple
Loops of Consanguinity) (Spence and Hodge, 2000; Young, 1999).
112 Bennett et al.
B. Offer genetic testing and screening as appropriate (see under Genetic
Screeningand Testingfor ConsanguineousCouples and TheirOffspring).
relationships (Ottenheimer, 1996). Mistaken societal beliefs in the “ills of cousin
unions” are deeply ingrained as noted by Dr Bell, a New England physician in
Perhapsno opinion,uponsubjects ofa medicalcharacter,is morewidelydiffusedamongthe
public, or more tenaciously held, than that the results of the marriage of blood relations are
by sheer force of these circumstances alone it has come to be regarded as an unquestioned
and unquestionable fact.
The history of hemophilia in the royal families of Europe in the 18th and 19th
centuries is often cited as an example of the detrimental effects of inbreeding,
even though the inheritance of this X-linked recessive condition would have oc-
A key component of genetic counseling is to ascertain the client’s precon-
ceivednotion of thenature and magnitude of genetic risks to their offspring(Baker
et al., 1998). If the client is from a culture where consanguineous unions are un-
common, discussing how frequent consanguineous unions occur in other parts of
the world can be reassuring. Providing historical examples of cousin couples may
also help to “normalize” their situation (e.g., Charles Darwin and his wife Emma
Wedgwood were ﬁrst cousins, as were Albert Einstein and his second wife Elsa
Einstein; Queen Elizabeth II and her husband Prince Philip are related as closer
than third cousins, etc.).
Consanguineous couples may keep their relationship hidden because of fears
of stigma, discrimination, ostracization, and even legal prosecution. Discussing
such fears and the attitudes of family and friends regarding their relationship is
important. If a consanguineous couple has a child with a congenital anomaly or a
geneticdisorder,theremay be anattitudeof“I told youso”amongfamilymembers
andacquaintances, adding tofeelings of parentalguilt. Providing a follow-upletter
after the genetic counseling session can clarify misconceptions that may circulate
among the couple’s family and peers.
Shame reactions to perceived or actual external disapproval, ridicule, and
scorn are also prominent in these families, particularly in the United States where
consanguinity has been traditionally frowned upon. Kessler (in Resta, 2000) and
Weil (2000) have written excellent reviews on the management of guilt and shame
reactions in a genetic counseling setting.
Consanguinity: Genetic Counseling and Screening 113
Psychosocial counseling concerning incestuous unions is complex, particu-
larly if the union involves a minor (Damon and Card, 1999; Maddock and Larson,
1995; Whetsell-Mitchell, 1995).Referral to specialized therapists and community
support services is indicated if such services are not already in place.
Identiﬁcation of positive carrier status may alter the person’s self-concept.
There may be an altered perception of genetic identity, changed relationships
with the family of origin, damage to self-esteem, altered social identity, altered
Rosell and DeVellis, 2000; Weil, 2000).
Immigrants to the United States and Canada from populations whereconsan-
guineous unions are common may have attitudes about the preference of consan-
guineous unions that are deeply embedded in cultural beliefs. Factors include the
desirabilityoffamiliaritywiththefamily’ssocialandbiological traits, and possible
bettertreatment by in-laws(AlwanandModell,1997; Bittles,1998,2001;Demirel
et al., 1997; Hussain, 1999; Panter-Brick, 1991; Shiloh et al., 1995). There may
be an economic rationale for keeping goods and property within a family. Genetic
counseling should explore the client’s cultural belief systems while being respect-
fulof clientbeliefs and culturaltraditions (Panter-Brick,1991;Shiloh etal., 1995).
A. Arrange/facilitateadditional appointments tocomplete thefamily history,
risk assessment, and testing considerations as indicated. Assist in refer-
rals for evaluation of abnormal tests or screening results (e.g., abnormal
ultrasound, positive neonatal screening, etc.).
B. A letter to the consultand(s) that includes a summary of major topics dis-
cussedinthe genetic counseling sessionishelpful(HallowellandMurton,
1998). The consultand(s) may also choose to share the letter to educate
family members and health professionals.
C. Provide the consultand/couple with names of support groups and re-
sources (see under Patient Resources).
The Cousin Couples website (www.cousincouples.com) provides access to
support services for cousins who are romantically involved. Ottenheimer (1996)
provides a historical perspective on the legal and cultural views of consanguinity
in the United States.
114 Bennett et al.
ETHICAL ISSUES AND SPECIAL CONSIDERATIONS
Genetic Testing for the Child of a Consanguineous
Union Placed for Adoption
A child of an incestuous union or even a nonincestuous consanguineous
union may be placed for adoption or in foster care because of legal and/or social
ramiﬁcations. Earlier publications on genetic testing of children from incestuous
unions suggestedpostponing permanent adoption until after 1 year of age, because
many diseases would not manifest until that time (Baird and McGillivray, 1982;
Hall, 1978; Harper, 1998). A child from a consanguineous union (incestuous or
otherwise) who is placed for adoption should not receive special consideration for
genetic testing beyond the recommendations for testing outlined under Genetic
Screening for Offspring of Consanguineous Unions. This policy is congruent with
the American Society of Human Genetics (ASHG) Social Issues Committee and
American College of Medical Genetics (ACMG) Social, Ethical, and Legal Issues
Committee statement on genetic testing in adoption (2000). This statement does
not support genetic testing for adoption that would not be performed on a child
“of a similar age for the purpose of diagnosis or of identifying appropriate pre-
vention strategies.” It further states that “genetic testing of newborns and children
in the adoption process should be limited to testing for conditions that manifest
themselves during childhood or for which preventive measures or therapies may
be undertaken during childhood.” However, prospective parents considering the
adoption of a child from a consanguineous union should receive genetic counsel-
ing as to the nature and probability of the risks for adverse outcomes, particularly
if the child is the product of an incestuous union.
Conﬁrming Parentage When Incest is Suspected
Given the potential legal consequences when incest is suspected, parentage
should be conﬁrmed and not assumed by history alone. Genetic counselors may
assist in facilitating the arrangement of DNA parentage studies and disclosure of
test results. Refer to www.genetests.org for a partial listing of laboratories that
perform parentage testing.
Populations With High Mean Coefﬁcients of Inbreeding
A couple may be related because they are members of a community isolate
that has many of its genes in common. A population that is geographically and/or
culturally isolated, or derived from a small founder population, may have clusters
ofrare autosomal recessivedisorders.Themeancoefﬁcientofinbreeding(α) value
is available for many of these population groups (Bittles, 1998; Bittles and Neel,
Consanguinity: Genetic Counseling and Screening 115
1994; Brown, 1951; Freire-Maia, 1968; Moore, 1987; Thomas et al., 1987). In
some genetic isolates, the mean coefﬁcient of inbreeding may approach the level
of ﬁrst cousins (F = 0.0625). Examples of the mean coefﬁcient of inbreeding for
select populations in North America are shown in Table I.
Pedigrees With Multiple Loops of Consanguinity
A couple may be related through more than one common ancestor, creating
multiple “loops” of consanguinity in a pedigree. Discussion of the mathematical
principles needed to calculate the coefﬁcient of inbreeding can be found in several
excellent sources (Harper, 1998; Spence and Hodge, 2000; Vogel and Motulsky,
1996; Young, 1999). Determining the F value is particularly important if a known
genetic condition or multifactorial disorder (such as cleft palate or a congenital
heart defect) is identiﬁed through pedigree analysis and medical record conﬁr-
mation. Multiple loops of consanguinity will affect genetic risk assessment and
possibly alter strategies for genetic testing and/or screening in the family.
Legal Ramiﬁcations of Consanguineous Unions
Thirtystatesinthe United States havelawsagainstcousinmarriages. The pro-
hibitions against cousin marriages are not based on empirical biological research
or genetic theory (Ottenheimer, 1996). Some laws do not distinguish biological
kin from married kin (e.g., prohibiting a stepfather from marrying a stepdaughter).
Becauseeachstatehas its ownuniquelawsagainstconsanguineousunions,genetic
counselors and other health professionals should have general knowledge about
the laws in their own state and neighboring states in their service area. Cousin
marriages are permitted throughout Western Europe. In the United States informa-
tion about a state’s law regarding consanguineous unions can be obtained from the
state genetics coordinator. Contact information for the state genetics coordinators
can be found at www.stategeneticscoordinators.org.
Romantic relationships between cousins are not infrequent in the United
States and Canada, and these unions are preferred marriages in many parts of the
world. The offspring of ﬁrst cousin unions are estimated to have about a 1.7–
2.8% increased risk for congenital defects above the population background risk
(Table III). There is an approximately 4.4% increased risk for prereproductive
mortality above the population background risk, some of which include major
congenitaldefects.The risk for anadversehealthoutcomeisgreatestin the 1styear
of life. The risk of an adverse health outcome in the pregnancy from an incestuous
union is difﬁcult to quantify because of ascertainment bias in all published studies.
116 Bennett et al.
The risk for adverse medical outcome in the offspring of incestuous unions is
probably in the range of 7–31% above population background, the risk being
greatest in the 1st year of life (Table IV).
There is a great deal of stigma associated with cousin unions in the United
States and Canada that has little biological basis. Health providers should provide
supportive counseling to these families and respect cultural belief systems. The
psychosocial issues for genetic counseling in the case of a cousin union are very
different from those for an incestuous union.
The most useful tool for genetic screening for consanguineous couples and
theiroffspringis a thorough medical familyhistory. Genetic counselors are unique-
testing on the basis of ethnicity should be offered to consanguineous couples, as
it would be to nonrelated couples. High-resolution ultrasound should be offered
at 20–22 weeks with maternal-serum marker screening at 15–18 weeks. For new-
borns that result from unions of second cousins or closer, supplemental neonatal
screening by tandem mass spectrometry by age 1 week should be offered in ad-
dition to the standard neonatal screening tests, with the goal of identifying poten-
tially treatable inborn errors of metabolism. Likewise, hearing screening should
be offered by age 3 months to identify hearing loss and to implement subsequent
language intervention. Care should be taken to assure that the offspring of consan-
These recommendations for genetic counseling and screening for consan-
guineous couples and their offspring are based on consensus opinion by an expert
committee with outside review.
Genetic counseling recommendations of the National Society of Genetic
Counselors (NSGC) are to assist practitioners in making decisions about appro-
priate management of genetic concerns. Each practice recommendation focuses
on a clinical or practice issue and is based on a review and analysis of the pro-
fessional literature. The information and recommendations reﬂect scientiﬁc and
clinical knowledge current as of the publication date and are subject to change
as advances in diagnostic techniques, treatments, and psychosocial understanding
emerge. In addition, variations in practice, taking into account the needs of the
individual patient and the resources and limitations unique to the institution or
type of practice, may warrant alternative approaches, treatments, or procedures
to the recommendations outlined in this document. Therefore, these recommen-
dations should not be construed as dictating an exclusive course of management,
nor does use of such recommendations guarantee a particular outcome. Genetic
counseling recommendations do not displace a health care provider’s best medical
Consanguinity: Genetic Counseling and Screening 117
This project was supported by a special projects grant from the National So-
ciety of Genetic Counselors and by Grant #5H46 MC00091-16 from the Maternal
and Child Health Bureau (Title V Social Security Act), Health Resources and Ser-
vices Administration, Department of Health and Human Services, to the Paciﬁc
Northwest Regional Genetic Group (PacNoRGG). We are grateful to the many
NSGC members and other experts who reviewed this document, and particularly
the members of theNSGC Genetic Services Committee andEthics Subcommittee.
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