Serotonin-Related Gene Polymorphisms and Central Nervous
System Serotonin Function
Redford B Williams*,1, Douglas A Marchuk2, Kishore M Gadde1, John C Barefoot1, Katherine Grichnik3,
Michael J Helms1, Cynthia M Kuhn4, James G Lewis5, Saul M Schanberg4, Mark Stafford-Smith3, Edward C
Suarez1, Greg L Clary1, Ingrid K Svenson2and Ilene C Siegler1
1Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, USA;2Department of Genetics, Duke University Medical
Center, USA;3Department of Anesthesiology, Duke University Medical Center, USA;4Department of Pharmacology and Cancer Biology, Duke
University Medical Center, USA;5Department of Pathology, Duke University Medical Center, USA
Central nervous system (CNS) serotonergic function affects a wide range of biological and behavioral functions affecting health and
disease. Our objective in this study was to determine whether functional polymorphisms of the genes that encode for the serotonin
transporter promoter (5HTTLPR) and monoamine oxidase A (MAOA-uVNTR) are associated with CNS serotonin turnoverFindexed
by cerebrospinal fluid levels of 5-hydroxyindoleacetic acid (5-HIAA)Fin a community sample of healthy adults. Subjects were 165
community volunteers without current medical or psychiatric illness, stratified with respect to ethnicity, gender, and socioeconomic status
who underwent inpatient evaluation in the General Clinical Research Center of a university medical center. A significant
ethnicity?genotype interaction (P¼0.008) indicated that, compared to the long/long and long/short genotypes, the 5HTTLPR
short/short genotype was associated with higher CSF 5-HIAA levels in African Americans, but with lower levels in Caucasians. A
gender?genotype interaction (P¼0.04) indicated that 5HTTLPR short/short genotype was associated with higher 5-HIAA levels in
women but with lower levels in men. MAOA-uVNTR 3.5 and 4 repeat alleles were associated with higher 5-HIAA (P¼0.03) levels in
men, but were unrelated to 5-HIAA levels in women. These findings suggest that effects of serotonin-related gene polymorphisms on
CNS serotonergic function vary as a function of both ethnicity and gender. Further research will be required to determine the
mechanism(s) underlying these differential effects. In the meanwhile, both ethnicity and gender should be taken into account in research
evaluating effects of these and related polymorphisms on CNS serotonergic function, as well as the broad range of biological and
behavioral functions that are regulated by CNS serotonergic function.
Neuropsychopharmacology (2003) 28, 533–541. doi:10.1038/sj.npp.1300054
Keywords: serotonin; 5HTTLPR; CSF 5-HIAA; ethnicity; gender; socioeconomic status
The neurotransmitter serotonin is involved in the regulation
of a broad array of psychological, behavioral, and biological
functions that when dysregulated influence the development
and course of an equally broad range of psychiatric and
medical disorders. Low central nervous system (CNS)
serotonergic function has been implicated, for example, in
the mediation of negative emotions, impulsive aggressive
behavior, increased use of alcohol and nicotine, increased
food consumption, increased sympathetic and decreased
parasympathetic nervous system outflow, and altered
neuroendocrine function (Williams, 1994, 1998). Periph-
erally, serotonin receptors and its transporter on platelets
(Greenberg et al, 1999), immune system cells (Mossner and
Lesch, 1998), cardiovascular system cells (Villalon and
Saxena, 1997), and gastrointestinal system cells (Gershon,
1999) play an important role in regulating the functions of
these organs and systems. These broad-ranging effects of
serotonin have led to the hypothesis that altered CNS
serotonergic function is a driver of the clustering of negative
moods, risky health behaviors, and altered biological
functions that increase disease risks in certain individuals
and groupsFfor example, lower socioeconomic status
(SES) (Williams, 1994, 1998).
Serotonergic function in both the CNS and peripheral
organs, tissues and cells is determined by complex
interactions among proteins involved in the enzymatically
mediated synthesis of serotonin from its amino acid
Online publication: 29 August 2002 at http://www.acnp.org/citations/
Received 9 August 2002; accepted 16 August 2002
Supported by National Heart, Lung, and Blood Institute Grant
K05MH79482, Clinical Research Unit Grant M01RR30, and the Duke
University Behavioral Medicine Research Center.
*Correspondence: Dr RB Williams, Department of Psychiatry and
Behavioral Sciences, Duke University Medical Center, Box 3926,
Durham, NC 27710, USA, Tel: +1 919 684 3863, Fax: +1 919 681
8960, E-mail: firstname.lastname@example.org
Neuropsychopharmacology (2003) 28, 533–541
& 2003 Nature Publishing Group All rights reserved 0893-133X/03 $25.00
precursor tryptophan, its reuptake after release, its en-
zymatically mediated breakdown, and its effects on a large
family of receptors on pre- and postsynaptic neurons as well
as cells in other tissues and organs. Many of the genes
encoding for these proteins have now been identified and
cloned, and a growing body of research has begun to
evaluate effects of variation in these candidate genes, in the
form of polymorphisms, on the functions influenced by the
The most intensively studied of these polymorphisms has
been a 44-base pair insertion/deletion polymorphism
(5HTTLPR) in the 50flanking regulatory region of the
serotonin transporter gene (17q11.1–q12) that is associated
with differential transcriptional efficiencies: both basal and
stimulated activity of the long (L) allele is approximately
twice that of the short (S) variant (Lesch et al, 1996). An
initial report showing the S allele to be associated with
increased levels of neuroticism and decreased levels of
agreeableness (assessed by the NEO Personality Inventory:
NEO-PI) in a predominantly male Caucasian sample (Lesch
et al, 1996) has not been replicated in several succeeding
studies (Flory et al, 1999; Gusavsson et al, 1999). This
failure to replicate the 5HTTLPR effects on personality
dimensions may be explained by reports showing that
gender and ethnicity moderate effects of 5HTTLPR
genotypes on negative mood indices, with the S allele
associated with higher negative moods in men and/or
Caucasians but associated with no effect or lower negative
mood levels in women and/or other ethnic groups
(Gelernter et al, 1998; Du et al, 2000). It should be noted,
however, that a recent study did replicate the association of
the S allele with higher neuroticism and lower agreeableness
in a female sample and showed the association not to be the
result of population stratification (Greenberg et al, 2000).
Another source of variability in findings across studies of
different populations is the observed variation in the
frequency of the L allele across populationsFranging from
more than 70% in Africa and African Americans to 50% in
Europeans to less than 30% in Japan (Gelernter et al, 1999).
This frequency variation could be associated with differ-
ences in allele effects. For example, the 5HTTLPR S allele
has been found to be associated with smoking behavior, via
interaction with neuroticism, in Caucasian samples (Ler-
man et al, 2000; Hu et al, 2000), but a recent study found the
L allele to be associated with smoking among Japanese
males (Ishikawa et al, 1999). Similarly, while the S allele is
associated with early-onset alcoholism and impulsive
violent behavior in European samples (Hammoumi et al,
1999; Hallikainen et al, 1999), in a Japanese population it
was the L allele that was found associated with alcohol-
related antisocial behavior (Ishiguro et al, 1999).
Furthermore, negative moods, alcohol abuse, and smok-
ing are functions that are complexly determined, not by a
single gene or specific environmental stimulus, but by the
effects of multiple genes interacting with each other and
with multiple aspects of the environment over time. It
should come as no surprise, therefore, that factors like
gender, ethnicity, and population are associated with
differences in the effects of polymorphisms of serotonin-
related genes on mood and behavior.
One approach to clarifying how genetic variation in the
serotonergic system affects the broad range of psychologi-
cal, behavioral, and biological functions regulated by
serotonergic function is to move ‘upstream’ from these
complexly determined characteristics and assess the effects
of polymorphisms of serotonin-related genes on more
direct biological indices of serotonergic function. CSF 5-
hydroxyindoleacetic acid (5-HIAA) levels provide such a
measure with respect to CNS serotonin turnover, especially
reflecting activity in the frontal cortex (Stanley et al, 1985;
Doudet et al, 1995). Low CNS serotonin function, as indexed
by CSF 5-HIAA, is under both genetic and environmental
control and correlates with impulsive and aggressive
behaviors, as well as tendencies toward alcohol abuse, in
nonhuman (Higley and Linnoila, 1997) and human primates
(Roy et al, 1988; Ballenger et al, 1979). We recently reported
(Williams et al, 2001) that persons with one or two copies of
the 5HTTLPR L allele have CSF 5-HIAA levels that are 50%
higher than those in persons with the S/S genotype, an
association that was not found, however, in a Swedish
sample (Jonsson et al, 1998).
Research focusing on a functional polymorphism of
another candidate gene known to influence serotonergic
function illustrates further the importance of sample
demographic characteristics in affecting associations be-
tween serotonin-related gene polymorphisms and CSF 5-
HIAA. A polymorphism (MAOA-uVNTR) in the upstream
regulatory region of the gene encoding for monoamine
oxidase A (MAOA), the enzyme that deaminates serotonin
and norepinephrine, contains a variable numberF2, 3, 3.5,
4, or 5Fof upstream tandem repeats (uVNTR) and has
been shown to affect the transcriptional efficiency of the
gene, in that alleles with 3.5 or 4 copies of the repeat
sequence are transcribed 2–10 times more efficiently than
those with 2, 3, or 5 copies of the repeat (Sabol et al, 1998).
The more efficient 3.5 and 4 repeat MAOA-uVNTR alleles
have been associated with higher levels of aggressiveness/
impulsivity and smaller CNS serotonergic responsivity
(indexed by prolactin response to fenfluramine) in one
study (Manuck et al, 2000). Another study found gender
differences in the effect of MAO-uVNTR genotypes on CNS
serotonin turnover, with the more efficient 3.5 and 4 alleles
associated with higher CSF 5-HIAA levels in women, but
with a nonsignificant trend toward lower levels in men
(Jonsson et al, 2000).
In the context of an investigation of the role of CNS
serotonergic turnover (indexed by CSF 5-HIAA levels) in
the clustering of psychosocial and biobehavioral risk
characterstics in lower SES groups, we have recruited a
large sample of healthy community volunteers, with
approximately equal proportions of men and women,
African Americans and Caucasians, and high and low SES
individuals, who undergo extensive testing during the
course of a 2-day admission to the Duke General Clinical
Research Center. We have also genotyped these subjects
with respect to the 5HTTLPR and MAOA-uVNTR poly-
morphisms, making it possible to evaluate the impact of
these polymorphisms on CNS serotonin turnover. The
unique nature of our sampleFa healthy community
volunteer cohort that is stratified for ethnicity, gender,
and SESFmakes it possible for us to determine whether the
ethnicity and gender moderation of the effects of these
polymorphisms on ‘soft’ behavioral measures is also found
for a more objective biological measure, CSF 5-HIAA.
Serotonin genes and CNS serotonin
Williams et al
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