title: Genetic and environmental correlates of semen quality: a twin study.
abstract: BACKGROUND
  The influences of environmental factors on the male reproductive system have been much debated over the last 3 decades. We studied the impact of genes and environment on semen quality, sex hormone levels, and sperm chromatin stability by using a twin design.
  
  
  METHODS
  The study population consisted of monozygotic and dizygotic twins from the population-based Danish Twin Registry and a random selection of pairs of singleton brothers from the Danish Civil Registration System. All men were 20 to 45 years of age. The study population comprised 100 monozygotic twin brothers (50 pairs), 102 dizygotic twins (51 pairs), and 102 single-born brothers (51 pairs). A semen sample and blood sample were collected from all participants.
  
  
  RESULTS
  Heritability was estimated to account for 20% (95% confidence interval = 0% to 68%) of the variation in sperm density. A higher heritability was found for the hormones reflecting Sertoli cell function (inhibin B, 76% [36% to 84%] and follicle-stimulating hormone, 81% [40% to 88%]) and for percent morphologic normal cells (41% [0% to 60%] and sperm chromatin parameters (mean alphaT, 68% [34% to 81%] and COMP alphaT, 72% [25% to 82%], respectively).
  
  
  CONCLUSIONS
  Our study indicates a substantial hereditary component in plasma levels of hormones reflecting Sertoli cell function and in sperm cell chromatin stability and morphology. The environmental contribution (including the prenatal environment) appeared to be largest for sperm count.
authors.affiliation: Department of Occupational Medicine, Aarhus University Hospital, Aarhus, Denmark. lstore@os.dk
authors.forename: Lone
authors.initials: L
authors.lastname: Storgaard
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Bonde
authors.forename: Erik
authors.initials: E
authors.lastname: Ernst
authors.forename: Claus Yding
authors.initials: CY
authors.lastname: Andersen
authors.forename: Marcello
authors.initials: M
authors.lastname: Spanô
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Petersen
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
mesh_terms: D000328:Adult; D003718:Denmark; D004777:Environment; D012739:Gonadal Steroid Hormones / Q000097:blood / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D012661:Semen; D013076:Sperm Count; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D012739:Gonadal Steroid Hormones