title: Dizygotic twinning.
abstract: The tendency to conceive spontaneous dizygotic (DZ) twins is a complex trait with important contributions from both environmental factors and genetic disposition. Twins are relatively common and occur on average 13 times per 1000 maternities, though the twinning frequency varies over time and geographic location. This variation is mostly attributed to the differences in DZ twinning rate, since the monozygotic twinning rate is relatively constant. DZ twinning is in part under genetic control, with mothers of DZ twins reporting significantly more female family members with DZ twins than mothers of monozygotic twins. Maternal factors such as genetic history, advanced age and increased parity are known to increase the risk of DZ twins. Recent research confirmed that taller mothers and mothers with a high body mass index (30>) are at greater risk of DZ twinning. Seasonality, smoking, oral contraceptive use and folic acid show less convincing associations with twinning. Genetic analysis is beginning to identify genes contributing to the variation in twinning. Mutations in one of these genes (growth differentiation factor 9) are significantly more frequent in mothers of DZ twins. However, the mutations are rare and only account for a small part of the genetic contribution for twinning.
authors.affiliation: Department of Biological Psychology, VU University Amsterdam, van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands. c.hoekstra@psy.vu.nl
authors.forename: Chantal
authors.initials: C
authors.lastname: Hoekstra
authors.forename: Zhen Zhen
authors.initials: ZZ
authors.lastname: Zhao
authors.forename: Cornelius B
authors.initials: CB
authors.lastname: Lambalk
authors.forename: Gonneke
authors.initials: G
authors.lastname: Willemsen
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
authors.forename: Grant W
authors.initials: GW
authors.lastname: Montgomery
mesh_terms: D000367:Age Factors; D000818:Animals; D055430:Bone Morphogenetic Protein 15; D005260:Female; D014644:Genetic Variation; D055429:Growth Differentiation Factor 9; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics; D011247:Pregnancy / Q000235:genetics; D015995:Prevalence; D016649:Primary Ovarian Insufficiency / Q000235:genetics; D027724:Reproductive Techniques, Assisted; D012641:Selection, Genetic; D014429:Twins, Dizygotic / Q000235:genetics
chemical_list: C525901:BMP15 protein, human; D055430:Bone Morphogenetic Protein 15; C525897:GDF9 protein, human; D055429:Growth Differentiation Factor 9; D036341:Intercellular Signaling Peptides and Proteins