[Three sets of twins in three successive generations through the maternal line]

It is generally held that there are genetic factors for dizygotic (DZ) twinning, but the pattern of inheritance is far from clear. We report on a rare pedigree with three sets of spontaneous DZ female twin births in three successive generations. To our knowledge no similar pedigrees have been reported in literature. Zygosity determination in three pairs of twins was performed with ABO, MN and Rh blood groups from erythrocytes and with STR analysis from samples of saliva. In our pedigree, the direct transmission of the DZ twinning through the maternal line seems show an autosomal dominant pattern of inheritance. We believe that the inheritance of DZ twinning appears to be recessive in most case and autosomal dominant only in rare instances. It is plausible with the hypothesis that the expression of the dizygotic twinning trait in a mother shows a genetic heterogeneity.