GENETIC MODELING OF DIZYGOTIC TWINNING IN PEDIGREES OF SPONTANEOUS DIZYGOTIC TWINS

The inheritance of spontaneous dizygotic (DZ) twinning was investigate d in 1,422 three-generation pedigrees ascertained through mothers of s pontaneous DZ proband twins, DZ twinning was modelled as a trait expre ssed only in women, The penetrance was modelled first as a parity inde pendent and secondly as parity dependent, The observed frequencies of maternal and paternal grandmothers with DZ twins differed significantl y from the expectations under an X-linked mode of inheritance, Complex segregation analysis showed that the parity-independent phenotype of ''having DZ twins'' was consistent with an autosomal monogenic dominan t model, with a gene frequency of 0.035 and a female-specific lifetime penetrance of 0.10, Recessive, polygenic, and sporadic models were re jected, The autosomal dominant model revealed a strong robustness agai nst a changing population prevalence and the loss of information due t o the presence of same-sexed twin pairs of unknown zygosity. When DZ t winning was modelled as a parity dependent trait, the data were compat ible with an autosomal dominant model with a gene frequency of 0.306 a nd a penetrance of 0.03 per birth for female gene carriers. (C) 1996 W iley-Liss, Inc.