Concordant contralateral lambdoidal synostosis in dizygotic twins.

Twin studies have been widely used to investigate genetic versus environmental causality of malformations. While there are numerous reports of concordant sutural fusions in syndromic twins, there are few cases in siblings with nonsyndromic single suture synostosis. Lambdoidal synostosis has no clear genetic etiology. Discordant synostosis has been reported in one monozygotic twin; there is also an unsubstantiated report of concordance in dizygotic twins. We describe dizygotic twins concordant for contralateral lambdoidal synostosis. Mutational analysis for FGFR 1,2,3 was negative. Given the low incidence, absence of reported inheritability, and lack of documented concordance in monozygotic twins, the pathogenesis of isolated lambdoidal fusion can only be ascribed to stochastic influences.