The relationship between stressful life events, the
serotonin transporter (5-HTTLPR) genotype and
NATHAN A. GILLESPIE*, JOHN B. WHITFIELD, BEN WILLIAMS,
ANDREW C. HEATH AND NICHOLAS G. MARTIN
Queensland Institute of Medical Research, Brisbane, Australia; Royal Prince Alfred Hospital, Sydney,
Australia; Department of Psychiatry, Washington University School of Medicine, St Louis, MO, USA
Background. Serotonin is a good candidate for major depression. We attempted to replicate the
study by Caspi and colleagues [Science (2003) 301, 386–389] which reported a significant interaction
between serotonin transporter (5-HTTLPR) genotype and stressful life events when predicting
Method. We typed the serotonin promoter 5-HTTLPR gene in 1206 male and female twins aged
19–78 years (mean=39, S.D.=11). A DSM-IV diagnosis of major depression was available for 1199
twins. Most of these twins had participated in a 1988–1990 study which included a stressful life
events inventory and self-report measure of depression based on the SCL-90 and DSSI/sAD. Com-
plete 5-HTT genotype and life events data, self-report symptoms and major depression diagnoses
were available for 1091 subjects. We regressed categorical and ordinal measures of depression onto
stressful life events and genotype.
Results. There were significant main effects for stressful life events but there was no evidence for
any effect of 5-HTT genotype, nor a genotyperstressful life event interaction.
Conclusions. Regardless of whether our results were based on binary logistic or ordinal regression
analyses we found no evidence to support a main effect of 5-HTTLPR, or an interaction between
the 5-HTTLPR genotype and stressful life events on major depression. Only 20% of our subjects
were aged below 30 years. It is possible that the effect reported by Caspi and colleagues is specific to
young people, in which case our study has much less power in this age group.
The serotonergic system is a strong genetic can-
didate for major depression and suicide. In their
review, Owens & Nemeroff (1994) highlighted
considerable evidence to support the hypothesis
that there are significant differences in the sero-
tonergic systems in patients with and without
major depression. It is known that the ‘s’ allele
of the polymorphism reduces the transcriptional
efficiency of this serotonin promoter, resulting
in decreased 5-HTT expression and serotonin
uptake in lymphoblasts (Lesch et al. 1996).
More recently, Caspi et al. (2003) have re-
ported that variation in the 5-HTT gene-linked
polymorphic region (5-HTTLPR) moderates the
influence of stressful life events (SLEs) on major
depression. Based on a sample of 1037 adults
aged 26 years, the influence of SLEs on the in-
cidence of major depression was significantly
greater amongst homozygous and heterozygous
carriers of the short(‘s’)allele in the 5-HTTLPR
genotype. The same genotype by environment
(GrE) interaction also approached significance
for suicidal behaviour.
Epidemiology Unit, Queensland Institute of Medical Research,
Post Office, Royal Brisbane Hospital, 300 Herston Road, Herston,
Qld 4029, Australia.
for correspondence:Nathan Gillespie,Genetic
Psychological Medicine, 2005, 35, 101–111.
f 2004 Cambridge University Press
Printed in the United Kingdom
Using a sample of Australian twins, the aim of
this study is to determine whether variation in
the serotonin transporter (5-HTTLPR) geno-
type moderates the influence of SLEs on major
depression and suicidal behaviour.
MATERIALS AND METHOD
Subjects were drawn from the Australian
National Health and Medical Research Council
Twin Register (ATR). The ATR is a volunteer
register founded in 1978 with approximately
25000 twins of all types and ages enrolled at
various stages of active participation. This rep-
resents approximately 10–20% of living twins
in Australia. Numerous analyses have shown
that the ATR is typical of the Australian popu-
lation in many respects including the prevalence
of psychiatric symptoms (Kendler et al. 1986),
although the ATR sample tends to be slightly
more middle class and educated than average,
particularly for males (Baker et al. 1996).
The current project was based on an older
cohort of 3808 twin pairs born before 1965
which was first surveyed during 1980–1982 and
was then followed up during 1988–1990to inves-
were obtained from 2997 complete twin pairs
and 334 singles, with an individual response rate
of 83%, and a complete pair response rate of
79%. At the same time, the 576 incomplete twin
pair respondents (singletons) and their co-twins
from the 1980–1982 study were also followed-up
with an identical questionnaire. The 1988–1990
study contained a lengthy self-report Health
and Lifestyle Questionnaire (HLQ) which in-
corporated many of the questions sent out to
the same twins 8 years previously such as
tobacco use, alcohol consumption, personality,
sociodemographic variables, psychiatric symp-
toms, SLEs, social attitudes and numerous
other behavioural measures (Heath et al. 1994).
of whom had been targeted for the 1988–1990
study, were approached and asked to participate
in a study which included a semi-structured
assessment for the genetics of alcoholism. We
set out to obtain blood samples from as many of
these twins as possible, selected only on the basis
of willingness to cooperate. Samples were ob-
tained from 3347 individual twins (comprising
1383 complete twin pairs and 581 singletons)
before funds were exhausted.
DNA extraction and genotyping
Genomic DNA was extracted (Miller et al. 1988)
from peripheral venous blood samples. Zygosity
of same-sex twins was determined by typing nine
independent DNA microsatellite polymorph-
isms at QIMR using the profiler AmpFLSTRR
Profiler PlusT multiplex marker set (Applied
Biosystems, Foster City, CA, USA). All twins
were also typed for ABO, Rh and MNS blood
groups by the Red Cross Blood Service in
Brisbane. Genotypes for the 5-HTTLPR poly-
morphism were determined using the method
described by Turker et al. (1998), with primers
5k-GGCGTTGCCGCTCTGAATGCC and 5k-
PCR products were separated on 7% polyacryl-
amide gel and visualized with ethidium bromide.
The product lengths were 221 bp (short allele)
and 265 bp (long allele).
Imputation of missing genotypes
There were 15 monozygotic twins with missing
imputed using their co-twin’s genotype. A total
of 1206 subjects had complete 5-HTTLPR
genotype information. The age range for this
sample was 19–78 years (mean=39 years, S.D.=
11 years). The sample was then split into three
groups on the basis of genotype. The frequencies
for the ‘ss’, ‘sl’ and ‘ll’ genotypes were 22%
(n=262), 48% (n=577) and 30% (n=367) re-
spectively. These were not significantly different
from Hardy–Weinberg equilibrium (x21=1.81),
although this was tested without regard to the
relatedness of twins. In addition, there was no
significant difference in genotype frequencies
between the sexes (x22=0.82, p=0.66). Popu-
lation stratification was unlikely given that more
than 95% of the subjects’ great-grandparents
were reported as being of northern European
ancestry, mainly from Britain and Ireland.
1988–1990 General Health Questionnaire
Details of the SLEs and self-report measures of
depression which formed part of the 1988–1990
questionnaire are described below.
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Stressful life events, the 5-HTTLPR genotype and major depression111