title: The Sex Ratio of Full and Half Siblings of People Diagnosed With ADHD in Childhood and Adolescence: A Danish Nationwide Register-Based Cohort Study.
abstract: OBJECTIVE
  It has been suggested that high levels of prenatal testosterone exposure are implied in the etiology of male preponderance disorders such as autism spectrum disorder and ADHD. Within this scope, we studied the sex ratio (proportion of males) in siblings of individuals diagnosed with ADHD in childhood and adolescence.
  
  
  METHODS
  We did a nationwide, register-based cohort study of the sex ratio in siblings of the 16,381 patients in Denmark diagnosed with ADHD at age 17 years and younger and registered in the nationwide Danish Psychiatric Central Register between January 1, 1994 and May 28, 2013.
  
  
  RESULTS
  Among the 33,151 siblings, 17,041 were males and 16,110 females. This yields a sex ratio of 0.514, which is not statistically significant different from the Danish live birth sex ratio of 0.513 during the relevant years (p = .70).
  
  
  CONCLUSIONS
  These findings provide no support for the hypothesis that the sex ratio is elevated among the siblings of people with ADHD.
authors.affiliation: Bispebjerg University Hospital, Copenhagen, Denmark Svend.Erik.Mouridsen@regionh.dk.
authors.forename: Svend Erik
authors.initials: SE
authors.lastname: Mouridsen
authors.affiliation: Hødersvej 5, Roskilde, Denmark.|International Rehabilitation Council for Torture Victims, Copenhagen, Denmark.
authors.forename: Bente
authors.initials: B
authors.lastname: Rich
authors.affiliation: Glostrup University Hospital, Denmark.
authors.forename: Torben
authors.initials: T
authors.lastname: Isager
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis* / Q000208:ethnology; D000067877:Autism Spectrum Disorder / Q000175:diagnosis* / Q000208:ethnology; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D008297:Male; D012042:Registries; D012307:Risk Factors; D012737:Sex Factors; D012744:Sex Ratio; D035781:Siblings; D044465:White People
keywords: ADHD; extreme male brain theory; sex ratio; testosterone