title: The Prenatal Environment in Twin Studies: A Review on Chorionicity.
abstract: A literature search was conducted to identify articles examining the association of chorionicity (e.g., whether twins share a single chorion and thus placenta or have separate chorions/placentas) and genetics, psychiatry/behavior, and neurological manifestations in humans twins and higher-order multiples. The main aim was to assess how frequently chorionicity has been examined in relation to heritability estimates, and to assess which phenotypes may be most sensitive to, or affected by, bias in heritability estimates because of chorionicity. Consistent with the theory that some chorionicity effects could lead to overestimation and others to underestimation of heritability, there were instances of each across the many phenotypes reviewed. However, firm conclusions should not be drawn since some of the outcomes were only examined in one or few studies and often sample sizes were small. While the evidence for bias due to chorionicity was mixed or null for many outcomes, results do, however, consistently suggest that heritability estimates are underestimated for measures of birth weight and early growth when chorionicity is not taken into account.
authors.affiliation: Division of Behavioral Genetics, Department of Psychiatry, Rhode Island Hospital, Providence, RI, USA.|Center for Alcohol and Addiction Studies, Brown University, Providence, RI, USA.|Division of Behavioral Genetics, Coro West Suite 204, 1 Hoppin St, Providence, RI, 02903, USA.
authors.forename: Kristine
authors.identifier: 0000-0002-8924-6597
authors.initials: K
authors.lastname: Marceau
authors.affiliation: EMGO Institute for Health and Care Research, VU University, Amsterdam, The Netherlands.
authors.forename: Minni T B
authors.initials: MT
authors.lastname: McMaster
authors.affiliation: Division of Behavioral Genetics, Department of Psychiatry, Rhode Island Hospital, Providence, RI, USA.|Department of Psychology and Child Development, California Polytechnic State University, San Luis Obispo, CA, USA.
authors.forename: Taylor F
authors.initials: TF
authors.lastname: Smith
authors.affiliation: Academic Medical Center, Medical Library, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Joost G
authors.initials: JG
authors.lastname: Daams
authors.affiliation: EMGO Institute for Health and Care Research, VU University, Amsterdam, The Netherlands.
authors.forename: Catharina E M
authors.initials: CE
authors.lastname: van Beijsterveldt
authors.affiliation: EMGO Institute for Health and Care Research, VU University, Amsterdam, The Netherlands. di.boomsma@vu.nl.
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
authors.affiliation: Division of Behavioral Genetics, Department of Psychiatry, Rhode Island Hospital, Providence, RI, USA.|Department of Psychiatry and Human Behavior, Brown University, Providence, RI, USA.
authors.forename: Valerie S
authors.initials: VS
authors.lastname: Knopik
mesh_terms: D002823:Chorion / Q000502:physiology*; D005260:Female; D005824:Genetics, Behavioral; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D019655:Quantitative Trait, Heritable; D018433:Twin Studies as Topic
keywords: Chorionicity; Genetics; Heritability; Prenatal environment; Twins