ORIGINAL INVESTIGATION
Brian S. Mustanski Æ Michael G. DuPree
Caroline M. Nievergelt Æ Sven Bocklandt
Nicholas J. Schork Æ Dean H. Hamer
A genomewide scan of male sexual orientation
Received: 16 September 2004 / Accepted: 30 November 2004 / Published online: 12 January 2005

Springer-Verlag 2005
Abstract This is the first report of a full genome scan of
sexual orientation in men. A sample of 456 individuals
from 146 families with two or more gay brothers was
genotyped with 403 microsatellite markers at 10-cM
intervals. Given that previously reported evidence of
maternal loading of transmission of sexual orientation
could indicate epigenetic factors acting on autosomal
genes, maximum likelihood estimations (mlod) scores
were calculated separated for maternal, paternal, and
combined transmission. The highest mlod score was
3.45 at a position near D7S798 in 7q36 with approximately
equivalent maternal and paternal contributions.
The second highest mlod score of 1.96 was located near
D8S505 in 8p12, again with equal maternal and paternal
contributions. A maternal origin effect was found near
marker D10S217 in 10q26, with a mlod score of 1.81 for
maternal meioses and no paternal contribution. We did
not find linkage to Xq28 in the full sample, but given the
previously reported evidence of linkage in this region, we
conducted supplemental analyses to clarify these findings.
First, we re-analyzed our previously reported data
and found a mlod of 6.47. We then re-analyzed our
current data, after limiting the sample to those families
previously reported, and found a mlod of 1.99. These
Xq28 findings are discussed in detail. The results of this
first genome screen for normal variation in the behavioral
trait of sexual orientation in males should
encourage efforts to replicate these findings in new
samples with denser linkage maps in the suggested regions.
Introduction
Although most males report primarily heterosexual
attractions, a significant minority (approximately 2%–
6%) of males report predominantly homosexual attractions
(Diamond 1993; Laumann et al. 1994; Wellings
et al. 1994). Multiple lines of evidence suggest that
biological factors play a role in explaining individual
differences in male sexual orientation (MIM 306995).
For example, the third interstitial nuclei of the human
anterior hypothalamus (INAH3), which is significantly
smaller in females, is also reported to be smaller in
homosexual males (LeVay 1991). Byne and colleagues
(2001) followed up on this finding by reporting a trend
for INAH3 to occupy a smaller volume in homosexual
men than in heterosexual men, with no significant difference
in the number of neurons within the nucleus.
Neuropsychological studies have reported differences in
performance with respect to tasks that show sex differences,
such as spatial processing (e.g., Rahman and
Wilson 2003), which may indicate differences in relevant
neural correlates (e.g., parietal cortex). The strong link
between adult sexual orientation and childhood gender-
Brian S. Mustanski and Michael G. DuPree contributed equally to
this work.
B. S. Mustanski Æ M. G. DuPree Æ S. Bocklandt
D. H. Hamer
Laboratory of Biochemistry, National Cancer Institute,
National Institutes of Health, Bethesda, Md., USA
B. S. Mustanski (&)
Institute for Juvenile Research Department of Psychiatry,
University of Illinois at Chicago (M/C 747),
1747 W. Roosevelt Road,
Chicago, IL 60608, USA
E-mail: bmustanski@psych.uic.edu
Tel.: +1-312-9969505
M. G. DuPree
Department of Anthropology,
Pennsylvania State University,
University Park, Pa., USA
C. M. Nievergelt Æ N. J. Schork
Department of Psychiatry,
University of California,
San Diego, Calif., USA
S. Bocklandt
Department of Human Genetics,
David Geffen School of Medicine at UCLA,
Los Angeles, Calif., USA
Hum Genet (2005) 116: 272–278
DOI 10.1007/s00439-004-1241-4
related traits expressed at an early age (Bailey and
Zucker 1995) suggests that such biological influences act
early in development, possibly prenatally. Similarly, the
correlation between sexual orientation and a variety of
prenatally canalized anthropometric traits suggests that
sexual orientation differentiation probably occurs before
birth (for a review, see Mustanski et al. 2002). Despite
this evidence, specific neurodevelopmental pathways
have yet to be elucidated.
Family and twin studies have provided evidence for a
genetic component to male sexual orientation. Family
studies, using a variety of ascertainment strategies,
document an elevation in the rate of homosexuality
among relatives of homosexual probands (for a review,
see Bailey and Pillard 1995). Several family studies report
evidence of increased maternal transmission of
male homosexuality (Hamer et al. 1993; Rice et al.
1999a), whereas others find no increase relative to
paternal transmission (Bailey et al. 1999; McKnight and
Malcolm 2000). Twin studies consistently show that
male sexual orientation is moderately heritable (for a
review, see Mustanski et al. 2002). For example, two
recent twin studies in population-based samples both
report moderate heritability estimates, with the remaining
variance being explained by nonshared environmental
influences (Kendler et al. 2000; Kirk et al. 2000).
The results from family and twin studies demonstrate
that sexual orientation is a complex (i.e., does not show
simple Medelian inheritance) and multifactorial phenotype.
A more limited number of studies have attempted to
map specific genes contributing to variation in sexual
orientation. Given the evidence for increased maternal
transmission, initial efforts focused on the X chromosome.
One study produced evidence of significant linkage,
based on Lander and Kruglyak (1995) criteria, to
markers on Xq28 (Hamer et al. 1993). Another study,
from the same laboratory but with a new sample, reported
a significant replication of these findings (Hu
et al. 1995). An independent group produced inconclusive
results regarding linkage to Xq28 (discussed in
Sanders and Dawood 2003) but did not publish the
findings in a peer-reviewed journal. All three of these
studies excluded families showing evidence for nonmaternal
transmission. A fourth study from another
independent group found no support for linkage, even
when excluding cases with suggestive father-to-son
transmission (Rice et al. 1999b). An analysis of the results
across all four studies produced a statistically
suggestive multiple scan probability (MSP) value of
0.00003 (Sanders and Dawood 2003). Two candidate
gene studies have been conducted, both producing null
results: one for the androgen receptor (AR; Macke et al.
1993) and another for aromatase (CYP19A1; Dupree
et al. 2004), on Xq12 and 15q21.2, respectively.
Given the complexity of sexual orientation, numerous
genes are likely to be involved, many of which are expected
to be autosomal rather than sex-linked. Indeed,
the modest levels of linkage that have been reported for
the X chromosome can account for, at most, only a
fraction of the overall heritability of male sexual orientation
as deduced from twin studies. Therefore, we have
undertaken a genomewide linkage scan to aid in the
identification of genes contributing to variation in sexual
orientation. As in previous studies, we diminished the
probability of false positives (i.e., gay men who identify
as heterosexual) by only studying self-identified gay
men. Unlike previous studies that have focused solely on
the X-chromosome and thus excluded families showing
evidence of non-maternal transmission, this study did
not use transmission pattern as an exclusion criteria. To
consider the possibility that previously reported evidence
of maternal loading of transmission of sexual orientation
was attributable to epigenetic factors acting on
autosomal genes, we calculated maximum likelihood
estimations (mlod) scores separated by maternal or
paternal transmission and the combined statistic. Based
on Lander and Kruglyak’s (1995) criteria, we found one
region of near significance and two regions close to the
criteria for suggestive linkage.
Materials and methods
Family ascertainment and assessment
The sample consisted of a total of 456 individuals from
146 unrelated families, of which 137 families had two gay
brothers and 9 families had three gay brothers. Thirty of
the families included one parent, and 30 of the families
included both parents. Additionally, 46 of the families
included at least one heterosexual male or female full
sibling (up to 6 additional siblings per family). The
sample included 40 families previously reported by Hamer
et al. (1993), 33 families previously reported by Hu
et al. (1995), and 73 previously unreported families. The
73 previously described families were selected for the
presence of two gay brothers with no indication of nonmaternal
transmission by the criteria described previously
(Hamer et al. 1993; Hu et al. 1995). For the 73 new
families, the sole inclusion criterion was the presence of
at least two self-acknowledged gay male siblings.
Subjects were recruited through advertisements in
local and national homophile publications as described
elsewhere (Hamer et al. 1993; Hu et al. 1995). The participants
were predominantly white (94.5%), college
educated (87.4%), and of middle to upper socioeconomic
status. The mean (SD) age for the gay siblings
was 36.98 (8.64). The protocol was approved by the NCI
Institutional Review Board, and each participant signed
an informed consent form prior to interview, questionnaire
completion, and the donation of blood for DNA
extraction.
Sexual orientation was assessed through a structured
interview or a questionnaire that included a sexual history
and the Kinsey scales of sexual attraction, fantasy,
behavior, and self-identification (Kinsey et al. 1948).
Each scale ranges from 0 (exclusively heterosexual) to 6
273
(exclusively homosexual). The mean (SD) of these four
scales for the gay males in this study was 5.65 (0.46).
Genotyping
DNA was extracted from peripheral blood by a commercial
service (Genetic Design, Greensboro, N.C.,
USA). A multiplex polymerase chain reaction (PCR)
was conducted as described (Dupree et al. 2004), with
403 microsatellite markers from the ABI PRISM Linkage
Mapping Set Version 2.5 with an average resolution
of 10 cM. Following the manufacturer’s guidelines,
products were analyzed on an ABI Prism 310 or 3100
and sized with the GeneScan version 3.1.2 program (PE
Biosystems, Foster City, Calif., USA), and genotypes
were assigned with the Genotyper version 3.6 program
(PE Biosystems). A PCR product from a DNA reference
sample (CEPH 1347-02) was used to monitor sizing
conformity (PE Biosystems). Across the 403 markers,
genotypes were ascertained on average for 95% of the
456 individuals. Mendelian incompatibilities (>0.05%
of genotypes) were removed from the data prior to
analyses by using the sib_clean routine from ASPEX
version 2.4 (Hinds and Risch 1996). The computer
program CERVUS 2.0 (Marshall et al. 1998) was em-
Fig. 1 Genome scan results.
The x-axis is the chromosome
location (cM), and the y-axis is
the mlod score. Graphics
included for combined (a),
maternal (b), and paternal (c)
meioses
274
ployed to test for deviation from the Hardy-Weinberg
equilibrium (HW) and to calculate polymorphism
information contents (PICs) at all loci. We found that
the markers had a mean (SD) PIC of 0.76 (0.08), and
1.31% of the markers deviated significantly from HW.
Statistical analyses
Nonparametric exclusion mapping of affected sib-pair
data (ASP) was performed by using ASPEX version 2.4
(Hinds and Risch 1996). ASPEX calculates the percentage
of identical by descent (%IBD) sharing and reports
the proportion of shared alleles of paternal,
maternal, and combined origin. The results for alleles of
combined origin also include alleles where the parental
origin is unknown. We calculated mlod with a linear
model and assuming a multiplicative model. The
ASPEX SIB_PHASE algorithm was applied; this uses
allele frequency information to reconstruct and to phase
missing parental information. Sex-specific recombination
maps were used for the calculation of multipoint
mlod scores. Marker order and map positions were
determined by using an integrated map (Nievergelt et al.
2004) based on the deCODE genetic map and updated
physical map information.
Results
Results from the multipoint analyses on chromosomes 1
through 22 are shown in Fig. 1 for paternal, maternal,
and combined meioses. Our complete genome scan for
male sexual orientation yielded three interesting peaks
with mlod scores greater than 1.8, located on chromosomes
7, 8, and 10. Table 1 contains additional information
concerning these peaks, including the nearest
marker, the location, MLOD, and allele sharing. Additionally,
Table 1 contains the approximate boundary of
the linkage peak, by reporting the approximate cM position
at which the mlod score declines below 1.0. For
chromosomes 7 and 8, the peak is a result of approximately
equal contributions from maternal and paternal
transmission, whereas a maternal-origin effect was
found for the peak on chromosome 10.
Figure 2 shows the multipoint mlod plots for the X
chromosome. Analyses of the full sample (dashed line)
did not produce any chromosomal regions with mlod
scores greater than 1.0. Given the previous evidence of
linkage to Xq28 with a portion of the sample reported
here (Hamer et al. 1993; Hu et al. 1995), we performed
supplemental analyses to determine why we did not find
linkage in the full sample. We began by re-analyzing the
data from the previously reported 73 families, which had
been selected for showing no evidence of paternal
transmission, by using updated marker positions (dotted
line). This produced a maximum mlod score of 6.47 for
markers in the Xq28 region. We then performed a
linkage analysis, with only the markers from the ABI
linkage mapping set, on these same 73 families. This
produced a maximum mlod score of 1.99 for markers in
the Xq28 region. Although the mlod score is higher
when using the current markers in the limited sample
compared with the full sample (1.99 vs. 0.35), it is still
significantly lower than the previously reported markers
in the limited sample. We provide Table 2 in order to
help clarify these results. Table 2 provides singlepoint
and multipoint results for the 73 previously reported
families on all markers ever reported from our group,
starting with the most telemeric new Xq28 marker.
Table 1 Chromosomal locations with nominally significant linkage peaks. The cM positions in parentheses indicate the boundary at which
the mlod score declines below 1.0. For chromosomes 7 and 8, the position is based on the combined map, but for chromosome 10, the
position is based on the female map
Nearby marker Location mlod Percentage
of sharing
cM Cyto Paternal Maternal Combined
D7S798 169.9 (155.1–end) 7q36 2.05 2.26 3.45 62.59
D8S505 54.2 (45.1–64.8) 8p12 1.38 0.93 1.96 60.10
D10S217 208.1 (201.8–217.4) 10q26
0.13 1.89 1.43 58.51
Fig. 2 Multipoint linkage analysis for the X chromosome. The xaxis
is the chromosome location (cM), and the y-axis is the mlod
score. —— Current markers with sample restricted to previously
reported families. - - - - Current markers with full sample. ......
Previously reported markers with previously reported families
275
Table 2 makes it clear that, although the multipoint
results suggest a dramatic change in mlod score between
the current markers and the previously reported markers
(6.47 vs. 1.99 for markers 0.62 cM apart), the singlepoint
results are not dramatically different (2.23 vs.
1.47). This difference is likely to be attributable to two
factors. First, the previous reports focused on the X
chromosome and contained many more markers in the
Xq28 region; the previously reported markers had an
average resolution of 1 marker every 1.12 cM, whereas
the current markers had an average resolution 6.97 cM
in the Xq28 region. The higher concentration of previously
reported markers surely allowed for the extraction
of more multipoint linkage information. Second, there
were more telomeric markers in the previously reported
mapping sets than in the current one. The singlepoint
results showed a trend for higher mlod scores closer to
the telomere, with the exception of JXYQ28, which had
a low PIC (0.28).
Discussion
This study reports results from the first full genome scan
for male sexual orientation. Using 73 previously reported
families and 73 new families with two or more
gay male siblings, we found three new regions of genetic
interest. Our strongest finding was on 7q36 with a
combined mlod score of 3.45 and equal contribution
from maternal and paternal allele transmission. This
score falls just short of Lander and Kruglyak’s (1995)
criteria for genomewide significance. Several interesting
candidate genes map to this region of chromosome 7.
Vasoactive intestinal peptide (VIP) receptor type 2
(VIPR2; MIM 601970) is a G protein-coupled receptor
that activates adenylate cyclase in response to VIP
(Metwali et al. 1996), which functions as a neurotransmitter
and as a neuroendocrine hormone. VIPR2 is
essential for the development of the hypothalamic suprachiasmatic
nucleus in mice (Harmar et al. 2002), which
makes it an interesting candidate gene for sexual orientation
in view of earlier reports of an enlarged suprachiasmatic
nucleus in homosexual men (Swaab and
Hofman 1990). Sonic hedgehog (SHH; MIM 600725)
plays an essential role in patterning the early embryo,
including hemisphere separation (Roessler et al. 1996)
and left to right asymmetry (Tsukui et al. 1999).
Homosexual men and women show a significant increase
in non-righthandedness, which is related to brain
asymmetry (Lalumiere et al. 2000).
Two additional regions approached the criteria for
suggestive linkage. The region near 8p12 contains several
interesting candidate genes, given the hypothesized
relationship between prenatal hormones and sexual
orientation (Mustanski et al. 2002). Gonadotropinreleasing
hormone 1 (GNRH1; MIM 152760) stimulates
both the synthesis and release of luteinizing hormone
and follicle-stimulating hormone, which are important
regulators of steroidogenesis in the gonads, and inhibits
the release of prolactin (Adelman et al. 1986). GnRH is
synthesized in the arcuate nucleus and other nuclei of the
hypothalamus (Kawakami et al. 1975). Steroidogenic
acute regulatory protein (STAR; MIM 600617) mediates
pregnenolone synthesis and is involved in the hypothalamic-
pituitary regulation of adrenal steroid production
(Sugawara et al. 1995), which in turn plays an important
role in sexual development. Neuregulin1 (NRG1; MIM
142445) produces a variety of isoforms that regulate the
growth and differentiation of neuronal and glial cells
through interaction with ERBB receptors (Burden and
Yarden 1997; Wen et al. 1994).
The 10q26 region is of special interest because it results
from excess sharing of maternal but not paternal
alleles. Previous studies have suggested that there is an
excess of homosexual family members related to the
proband through the mother, and we have proposed
previously that this might result in part from genomic
imprinting (Bocklandt and Hamer 2003). In support of a
connection between 10q26 and imprinting, a germline
differentially methylated region has been identified at
this location by Strichman-Almashanu et al. (2002) who
performed a genomewide screen for normally methylated
CpG islands and found 12 regions to be differentially
methylated in uniparental tissues of germline
origin, i.e., hydatidiform moles (paternal origin) and
complete ovarian teratomas (maternal origin). Such
CpG islands can regulate the expression of imprinted
genes over distances of several hundred kilobases. The
region around the 10q26 CpG islands includes the brainexpressed
gene Shadow of Prion Protein (SPRN), several
transcription regulators (ZNF511, VENTX2; MIM
607158), neurotransmitter interacting proteins
(DRD1IP; MIM 604647), and cell signaling pathway
proteins (INPP5A; MIM 600106, GPR123).
Table 2 Supplemental analyses comparing Xq28 results across
markers reported on in 1995, 1997, and the current report. All
analyses reported here are based on the sample restricted to those
families previously reported. Current markers and previously reported
markers were analyzed separately for the purpose of calculating
multipoint mlod scores
Marker Study year Location
(cM)
Marker distance
(cM)
Multipoint mlod
(previous markers)
Multipoint mlod
(current markers)
Singlepoint
mlod
DXS1073 Current 188.22 1.99 1.47
F8C 1993 188.84 0.62 6.47 2.23
DXS1108 1993 190.32 1.47 6.27 4.22
JXYQ28 1995 190.47 0.15 6.28 0.48
DXYS154 1993 190.79 0.32 5.71 3.53
276
Four previous linkage studies have been conducted
on the X chromosome and together produce a statistically
suggestive MSP in the Xq28 region (Sanders and
Dawood 2003). Because the focus of this study was a full
genome scan with the ABI linkage mapping set on a
partially new set of families, we began by reporting results
for these markers on the full sample. This analysis
did not produce evidence of linkage in the Xq28 region;
therefore, we conducted supplemental analyses to clarify
this result given previous findings. Our first supplemental
analysis combined results from the two previous
reports from our group (Hamer et al. 1993; Hu et al.
1995) in order to determine the magnitude of the linkage
signal in the 73 previously reported families that currently
comprised half of the current sample. This produced
a mlod of 6.47. To determine whether the lack of
linkage evidence in the full sample was attributable to
the new markers or the additional families (who were
not selected based on family transmission patterns), we
then conducted analyses on the previously reported
families by using the markers from the ABI linkage
mapping set. This produced an mlod score of 1.99. Table
2, which provides a summary of the single point and
multipoint results for this comparison, suggests that that
the difference in mlod score between the restricted
sample with the old and new markers is attributable to
the non-optimal position and density of the new markers.
The difference in mlod scores between the full
sample and the sample restricted to families without
evidence of paternal transmission (with the goal of
enriching the sample for families showing maternal
transmission) denotes the possibility of etiologic heterogeneity
for the proposed Xq28 locus.
Several limitations of the current study should be
noted. First, we were unable to calculate empirically
derived significance levels for this project because none
of the simulation programs that currently exist allow for
the use of sex-specific maps with ASP data. Future
development of simulation programs that allow for the
incorporation of this important information will prevent
this limitation in the future. Second, our marker set had
an average resolution of 10 cM, which may have led to
underestimated mlod scores. We discuss in detail above
the likely negative effects that this had on our X chromosome
results. Optimally, genome scans are followed
up with dense markers placed in promising regions, but
because of financial limitations, we were unable to do
this. Future studies will undoubtedly employ more
sophisticated and dense marker sets. Third, we analyzed
only 146 independent families, which is a small sample
for a complex trait such as sexual orientation. Approximately
half of these families have previously been included
in reports on the X chromosome (Hamer et al.
1993; Hu et al. 1995). Future research should be conducted
on a new and larger sample of participants. Our
linkage results should be interpreted with consideration
of the fact that we only included families with two selfidentified
gay brothers. Our results may not extrapolate
to individuals who do not meet our exclusion criteria,
such as individuals who engage in same-sex behavior but
do not identify as gay or individuals who identify as
bisexual. The definition of homosexuality is complicated,
and future genetic research would benefit from
additional phenotype development or the identification
of endophenotypes for sexual orientation (Mustanski
et al. 2002). The identification of basic processes that
underlie sexual orientation could increase the power of
future genetic studies. A related limitation is that we did
not include females in our study because it is not yet
clear if female sexual orientation is determined by the
same factors as male sexual orientation (for a discussion,
see Mustanski et al. 2002). Future research with mixsexed
samples should help to answer this question. Finally,
we did not collect data on the number of older
brothers, which shows a robust association with male
sexual orientation (Blanchard 2004). Future studies
should collect this data to allow for explorations of gene
by environment interactions; this could increase the
ability to identify genetic loci and also help to elucidate
the process linking number of older brothers to sexual
orientation.
In summary, we report the first genome scan for loci
involved in the complex phenotype of male sexual orientation.
We have also identified several chromosomal
regions and candidate genes for future exploration. The
molecular analysis of genes involved in sexual orientation
could greatly advance our understanding of human
variation, evolution, and brain development. In the absence
of obvious animal models, genetic linkage and
association studies provide the best opportunity for
discovering these loci.
Acknowledgements We thank all the individuals who participated
in the project for their time and openness and Lynn Goldin and
Danielle Dick for comments on the manuscript. B.S.M. was supported
by a NSF Graduate Research Fellowship and an NIH
Summer Research Fellowship. N.J.S. and C.M.N. were supported
in part by the NHLBI Family Blood Pressure Program (FBPP;
HL64777-01).
References
Adelman JP, Mason AJ, Hayflick JS, Seeburg PH (1986) Isolation
of the gene and hypothalamic cDNA for the common precursor
of gonadotropin-releasing hormone and prolactin releaseinhibiting
factor in human and rat. Proc Natl Acad Sci USA
83:179–183
Bailey JM, Pillard RC (1995) Genetics of human sexual orientation.
Annu Rev Sex Res 60:126–150
Bailey JM, Zucker KJ (1995) Childhood sex-typed behavior and
sexual orientation: a conceptual analysis and quantitative review.
Dev Psych 31:43–55
Bailey JM, Pillard RC, Dawood K, Miller MB, Farrer LA, Trivedi
S, Murphy RL (1999) A family history study of male sexual
orientation using three independent samples. Behav Genet
29:79–86
Blanchard R (2004) Quantitative and theoretical analyses of the
relation between older brothers and homosexuality in men.
J Theor Biol 230:173–187
Bocklandt S, Hamer DH (2003) Beyond hormones: a novel
hypothesis for the biological basis of male sexual orientation.
J Endocrinol Invest 26:8–12
277
Burden S, Yarden Y (1997) Neuregulins and their receptors: a
versatile signaling module in organogenesis and oncogenesis.
Neuron 18:847–855
Byne W, Tobet S, Mattiace L, Lasco MS, Kemether E, Edgar MA,
Morgello S, Buchsbaum MS, Jones LB (2001) The interstitial
nuclei of the human anterior hypothalamus: an investigation of
variation within sex, sexual orientation and HIV status. Hormones
Behav 40:86–92
Diamond M (1993) Homosexuality and bisexuality in different
populations. Arch Sex Behav 22:291–310
Dupree MG, Mustanski BS, Bocklandt S, Nievergelt C, Hamer
DH (2004) A candidate gene study of CYP19 (aromatase) and
male sexual orientation. Behav Genet 34:243–250
Hamer D (1999) Genetics and male sexual orientation. Science
285:803
Hamer DH, Hu S, Magnuson VL, Hu N, Pattatucci AM (1993) A
linkage between DNA markers on the X chromosome and male
sexual orientation. Science 261:321–327
Harmar AJ, Marston HM, Shen S, Spratt C, West KM, Sheward
WJ, Morrison CF, Dorin JR, Piggins HD, Reubi JC, Kelly JS,
Maywood ES, Hastings MH (2002) The VPAC(2) receptor is
essential for circadian function in the mouse suprachiasmatic
nuclei. Cell 109:497–508
Hinds D, Risch N (1996) The ASPEX package: affected sib-pair
exclusion mapping [computer program]. Stanford University,
Stanford
Hu S, Pattatucci A, Patterson C, Li L, Fulker D, Cherny S,
Kruglyak L, Hamer D (1995) Linkage between sexual orientation
and chromosome Xq28 in males but not females. Nat
Genet 11:248–256
Kawakami M, Negoro H, Kimura F, Higuchi T, Asai T (1975)
Neural control of LH release in anterior periventriculo-median
eminence-pituitary system. Neuroendocrinology 19:137–149
Kendler KS, Thornton LM, Gilman SE, Kessler RC (2000) Sexual
orientation in a U.S. national sample of twin and nontwin
sibling pairs. Am J Psychiatry 157:1843–1846
Kinsey AC, Pomeroy WB, Martin CE (1948) Sexual behavior in
the human male. Indiana University Press, Bloomington
Kirk KM, Bailey JM, Dunne MP, Martin NG (2000) Measurement
models for sexual orientation in a community twin sample.
Behav Genet 30:345–356
Lalumiere ML, Blanchard R, Zucker KJ (2000) Sexual orientation
and handedness in men and women: a meta-analysis. Psychol
Bull 126:575–592
Lander E, Kruglyak L (1995) Genetic dissection of complex traits:
guidelines for interpreting and reporting linkage results. Nat
Genet 11:241–247
Laumann EO, Gagnon JH, Michael RT, Michaels S (1994) The
social organization of sexuality: sexual practices in the United
States. University of Chicago Press, Chicago
LeVay S (1991) A difference in hypothalamic structure between
heterosexual and homosexual men. Science 253:1034–1037
Macke JP, Hu N, Hu S, Bailey M, King VL, Brown T, Hamer D,
Nathans J (1993) Sequence variation in the androgen receptor
gene is not a common determinant of male sexual orientation.
Am J Hum Genet 53:844–852
Marshall TC, Slate J, Kruuk L, Pemberton JM (1998) Statistical
confidence for likelihood-based paternity inference in natural
populations. Mol Ecol 7:639–655
McKnight J, Malcolm J (2000) Is male homosexuality maternally
linked? Psych Evol Gender 2:229–239
Metwali A, Elliott D, Blum AM, Li J, Sandor M, Weinstock JV
(1996) T cell vasoactive intestinal peptide receptor subtype
expression differs between granulomas and spleen of schistosome-
infected mice. J Immunol 157:265–270
Mustanski BS, Chivers ML, Bailey JM (2002) A critical review of
recent biological research on human sexual orientation. Annu
Rev Sex Res 12:89–140
Nievergelt CM, Smith DW, Kohlenberg JB, Schork NJ (2004)
Large-scale integration of human genetic and physical maps.
Genome Res 14:1199–1205
Rahman Q, Wilson GD (2003) Sexual orientation and the 2nd to
4th finger length ratio: evidence for organising effects of sex
hormones or developmental instability? Psychoneuroendocrinology
28:288–303
Rice G, Risch N, Ebers G (1999a) Genetics and male sexual orientation.
Science 28:803
Rice G, Anderson C, Risch N, Ebers G (1999b) Male homosexuality:
absence of linkage to microsatellite markers at Xq28.
Science 284:665–667
Roessler E, Belloni E, Gaudenz K, Jay P, Berta P, Scherer SW,
Tsui LC, Muenke M (1996) Mutations in the human Sonic
Hedgehog gene cause holoprosencephaly. Nat Genet 14:357–
360
Sanders AR, Dawood K (2003) Sexual orientation. In: Nature
Encyclopedia of Life Sciences. Nature Publishing Group, London
(http://www.els.net/els/public/search/search_public.asp)
Strichman-Almashanu LZ, Lee RS, Onyango PO, Perlman E, Flam
F, Frieman MB, Feinberg AP (2002) A genome-wide screen for
normally methylated human CpG islands that can identify
novel imprinted genes. Genome Res 12:543–554
Sugawara T, Holt JA, Driscoll D, Strauss JF III, Lin D, Miller
WL, Patterson D, Clancy KP, Hart IM, Clark BJ, et al (1995)
Human steroidogenic acute regulatory protein: functional
activity in COS-1 cells, tissue-specific expression, and mapping
of the structural gene to 8p11.2 and a pseudogene to chromosome
13. Proc Natl Acad Sci USA 92:4778–4782
Swaab DF, Hofman MA (1990) An enlarged suprachiasmatic
nucleus in homosexual men. Brain Res 24:141–148
Tsukui T, Capdevila J, Tamura K, Ruiz-Lozano P, Rodriguez-
Esteban C, Yonei-Tamura S, Magallon J, Chandraratna RA,
Chien K, Blumberg B, Evans RM, Belmonte JC (1999) Multiple
left-right asymmetry defects in Shh(
/
) mutant mice unveil a
convergence of the shh and retinoic acid pathways in the control
of Lefty-1. Proc Natl Acad Sci USA 96:11376–11381
Wellings K, Field J, Johnson A, Wadsworth J (1994) Sexual
behaviour in Britain. Penguin Books, New York
Wen D, Suggs SV, Karunagaran D, Liu N, Cupples RL, Luo Y,
Janssen AM, Ben-Baruch N, Trollinger DB, Jacobsen VL, et al
(1994) Structural and functional aspects of the multiplicity of
Neu differentiation factors. Mol Cell Biol 14:1909–1919
278
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