Psychological Medicine (2015), 45, 1379–1388. © Cambridge University Press 2014 ORIGINAL ARTICLE doi:10.1017/S0033291714002451 Genome-wide scan demonstrates significant linkage for male sexual orientation A. R. Sanders1,2*, E. R. Martin3, G. W. Beecham3, S. Guo3, K. Dawood4, G. Rieger5, J. A. Badner2, E. S. Gershon2, R. S. Krishnappa6, A. B. Kolundzija7, J. Duan1,2, P. V. Gejman1,2 and J. M. Bailey8 1 Department of Psychiatry and Behavioral Sciences, NorthShore University HealthSystem Research Institute, Evanston, IL, USA 2 Department of Psychiatry and Behavioral Neuroscience, University of Chicago, Chicago, IL, USA 3 Department of Human Genetics, University of Miami, Miami, FL, USA 4 Department of Psychology, Pennsylvania State University, University Park, PA, USA 5 Department of Psychology, University of Essex, Colchester, England, UK 6 Department of Psychiatry, Icahn School of Medicine at Mount Sinai, Elmhurst, NY, USA 7 Department of Sociomedical Sciences, Mailman School of Public Health, Columbia University, New York, NY, USA 8 Department of Psychology, Northwestern University, Evanston, IL, USA Background. Findings from family and twin studies support a genetic contribution to the development of sexual orien- tation in men. However, previous studies have yielded conflicting evidence for linkage to chromosome Xq28. Method. We conducted a genome-wide linkage scan on 409 independent pairs of homosexual brothers (908 analyzed individuals in 384 families), by far the largest study of its kind to date. Results. We identified two regions of linkage: the pericentromeric region on chromosome 8 (maximum two-point LOD = 4.08, maximum multipoint LOD = 2.59), which overlaps with the second strongest region from a previous separate link- age scan of 155 brother pairs; and Xq28 (maximum two-point LOD = 2.99, maximum multipoint LOD = 2.76), which was also implicated in prior research. Conclusions. Results, especially in the context of past studies, support the existence of genes on pericentromeric chro- mosome 8 and chromosome Xq28 influencing development of male sexual orientation. Received 28 April 2014; Revised 2 September 2014; Accepted 7 September 2014; First published online 17 November 2014 Key words: Chromosome 8, chromosome Xq28, complex trait, genome-wide linkage scan, human, male sexual orientation. Introduction of homosexuality, higher rates of bisexuality, and less temporal stability (Laumann et al. 1994b; Bailey et al. Sexual orientation, the sustained erotic attraction to 2000; Diamond, 2008a, b). Although our focus is male members of one’s own sex, the opposite sex, or both – sexual orientation, we note that female sexual orien- homosexuality, heterosexuality, or bisexuality, respect- tation also appears moderately heritable (Bailey et al. ively – is a primary component of human sexuality. 2000; Alanko et al. 2010; Langstrom et al. 2010; Burri Although Kinsey proposed that sexual orientation et al. 2011). Accurate prevalence estimates are currently exists upon a continuum reflected by his scale difficult to obtain, but the following two conclusions (Kinsey et al. 1948), male sexual orientation tends to are uncontroversial: homosexual orientation is much be bimodally distributed, with most men rating them- less common than heterosexual orientation among selves as predominantly heterosexual (Kinsey scale 0–1) men, but it is not rare in respondents in Western indus- or homosexual (Kinsey scale 5–6) (Laumann et al. trialized nations. For example, in a large and careful 1994b; Pillard & Bailey, 1998; Bailey et al. 2000). In con- survey of American males approximately 2% rated trast, women have a more continuous distribution their sexual orientation as homosexual when defined across the non-heterosexual orientations, lower rates as identity, 3–4% when defined psychologically (i.e. attraction and fantasy), and a few more did so when defined behaviorally (Laumann et al. 1994a). Partially * Address for correspondence: A. R. Sanders, M.D., Department of independent familial aggregation of male and female Psychiatry and Behavioral Sciences, NorthShore University homosexuality (Pillard & Weinrich, 1986; Bailey & HealthSystem Research Institute, 1001 University Place, Evanston, IL 60201, USA. Bell, 1993; Bailey & Benishay, 1993; Bailey et al. 1993, (Email: [email protected]) 1999; Pattatucci & Hamer, 1995; Schwartz et al. 2010) 1380 A. R. Sanders et al. further suggests the utility of separate analyses by sex. by improvements in statistical power with a larger Genetic epidemiological studies (family, twin, and seg- sample. regation analyses; see reviews by Mustanski et al. 2002; Schwartz et al. 2010) of males have shown (1) homo- sexuality to be more common in biological relatives Method of homosexual men compared to relatives of heterosex- Sample collection ual men (or than expected from population surveys), with the sibling recurrence ratios falling between ∼2 We recruited families with two or more homosexual and ∼4 (Pillard & Weinrich, 1986; Bailey & Pillard, brothers in several primarily English-speaking coun- 1991; Bailey & Bell, 1993; Hamer et al. 1993; Bailey ties, especially the United States, resulting in com- et al. 1999; Schwartz et al. 2010); (2) genetic contribu- pleted families from the United States (98.2%), tions suggested by higher concordances of sexual Canada (1.6%), and the United Kingdom (0.2%). We orientation for identical twins compared with same-sex excluded families known to have previously partici- fraternal twins (Bailey et al. 2000; Kendler et al. 2000; pated in other linkage studies of sexual orientation. Kirk et al. 2000; Santtila et al. 2008; Alanko et al. 2010; Our primary source for identifying probands was Langstrom et al. 2010); (3) environmental contributions through booths at community festivals, especially evidenced by monozygotic concordances far less than Gay Pride and related festivals. We also publicized unity, with the best demonstrated specific environmen- our study through advertisements and articles in tal influence being the fraternal birth order effect homophile media, liaisons with analogous groups (Blanchard & Bogaert, 1996); and (4) non-Mendelian (e.g. chapters of PFLAG; Parents, Families and segregation patterns (Bailey et al. 1999; Rice et al. Friends of Lesbians and Gays), and through an edu- 1999a; Schwartz et al. 2010). Furthermore, genetic stud- cationally oriented internet site (gaybros.com). We en- ies show some support for excess maternal trans- rolled other interested members (available parents and mission (Hamer et al. 1993), whose presence would any brothers, regardless of sexual orientation) in a fam- be consistent with X-linkage and which motivated fo- ily through the proband. The large majority (97.9%) of cusing initial linkage approaches to the trait on chro- the studied families were of European ancestry, 1.6% mosome X, although most studies have not found were African American, and 0.5% were Asian; 95.1% excess maternal transmission (Bailey et al. 1999; Rice were non-Hispanic and 4.9% were Hispanic. The aver- et al. 1999b; Schwartz et al. 2010). The aggregate evi- age age of the studied brothers was 44.3 years [range – dence suggests multifactorial causation of male sexual 18.7 88.9, standard deviation (S.D.) = 10.7], and the orientation, both genetic and environmental (i.e. a sample was recruited from 2004 to 2008. Brothers com- complex genetics scenario). pleted a self-report questionnaire, and all subjects All previous genetic linkage studies of male sexual provided a DNA sample via blood (EDTA lavender orientation were conducted on smaller sample sets. top tubes, with venipuncture performed primarily The two initial studies reported linkage to Xq28: first through a vendor: LabCorp is the Laboratory in 40 pairs of homosexual brothers (Hamer et al. Corporation of America, LabCorp, www.labcorp. 1993) and then further supported in 33 additional com) or saliva (Oragene DNA Self-Collection kits, such pairs (Hu et al. 1995). However, Xq28 linkage DNA Genotek, Canada). We obtained institutional re- was not supported in three subsequent studies of 54 view board approval from NorthShore University US pairs of homosexual brothers (Sanders et al. 1998), HealthSystem, and also convened and utilized a com- 52 Canadian pairs of homosexual brothers (Rice et al. munity advisory board. After complete description of 1999a), or 73 additional pairs of homosexual brothers the study to the subjects, all enrolled subjects provided studied by the original research group (Mustanski written informed consent. et al. 2005). Extended family samples [55 Canadian families (Ramagopalan et al. 2010) and 146 US families Ethical standards with 155 independent pairs of homosexual brothers The authors assert that all procedures contributing to (Mustanski et al. 2005)] that underwent genome-wide this work comply with the ethical standards of the rel- linkage scans (GWLS) found neither genome-wide evant national and institutional committees on human fi signi cant linkage nor any further support for experimentation and with the Helsinki Declaration of fi Xq28 linkage. The strongest ndings from the larger 1975, as revised in 2008. of the reported GWLS were at chromosomes 7qtel (∼7q35–q36), pericentromeric 8 (∼8p21–p11), and Measurement of sexual orientation 10qtel (∼10q26) (Mustanski et al. 2005). We chose to study male sexual orientation with an independent We assessed male sexual orientation as a primarily sample in a GWLS to seek more consistent findings bimodal, psychological trait. Using data from