title: Heritability of reproductive hormones in adult male twins.
abstract: BACKGROUND
  Proper functioning of the male reproductive axis depends on complex feedback systems between several hormones. In this study, the genetic contribution of various endocrine components of the hypothalamic-pituitary-testicular axis is evaluated and previously observed differences in FSH and inhibin B levels between mono- (MZ) and dizygotic (DZ) twins are re-investigated.
  
  
  METHODS
  Inhibin B, FSH, LH, sex hormone-binding globulin (SHBG) and testosterone levels were assayed in 128 adult males (20 MZ twin pairs, 7 single MZ twins, 10 DZ twin pairs, 27 single DZ twins and 34 siblings of twins, constituting 10 sibling pairs), aged 15.6-68.7 years. Hormone levels were compared across zygosity groups and heritability estimates were obtained using maximum likelihood variance component analysis.
  
  
  RESULTS
  Heritability estimates ranged from 56% (testosterone) to 81% (inhibin B and SHBG). For LH and FSH, the heritability was estimated at 68% and 80% respectively. No mean differences in hormone levels were observed across groups.
  
  
  CONCLUSIONS
  All measured hormones are highly heritable. A difference in the FSH-inhibin B feedback system between DZ twin males and MZ twin males could not be confirmed.
authors.affiliation: Division of Reproductive Medicine, Department of Obstetrics and Gynaecology, VU University Medical Center, 1007 MB Amsterdam, The Netherlands. e.kuijper@vumc.nl
authors.forename: E A M
authors.initials: EA
authors.lastname: Kuijper
authors.forename: C B
authors.initials: CB
authors.lastname: Lambalk
authors.forename: D I
authors.initials: DI
authors.lastname: Boomsma
authors.forename: S
authors.initials: S
authors.lastname: van der Sluis
authors.forename: M A
authors.initials: MA
authors.lastname: Blankenstein
authors.forename: E J C
authors.initials: EJ
authors.lastname: de Geus
authors.forename: D
authors.initials: D
authors.lastname: Posthuma
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005640:Follicle Stimulating Hormone / Q000235:genetics*; D006801:Humans; D007265:Inhibins / Q000235:genetics*; D007986:Luteinizing Hormone / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D012738:Sex Hormone-Binding Globulin / Q000235:genetics*; D013739:Testosterone / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D012738:Sex Hormone-Binding Globulin; C422364:inhibin B; D013739:Testosterone; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone