SEGREGATION DISTORTION IN THE OFFSPRING OF AFRO-AMERICAN FATHERS WITHPOSTAXIAL POLYDACTYLY

The unclear pattern of inheritance of postaxial polydactyly prompted t his search for evidence of imprinting or change of expression in males and females using material of the Latin American Collaborative Study of Congenital Malformations, The frequency of affected offspring for 1 96 fathers with polydactyly was compared with that for 233 mothers wit h the same condition, stratified according to African and non-African ancestry, The postaxial poIydactyly prevalence rate among the offsprin g of affected black fathers (44%) was larger than that in the group of affected black mothers (31%), with no difference between affected non black fathers (34%) and affected nonblack mothers (33%). The sex ratio (.51) observed in 631 black propositi and in 829 nonblack propositi w ith polydactyly (.58) could be a further indication of etiologic heter ogeneity for polydactyly between these two ethnic groups. The segregat ion distortion in favor of affecteds among the offspring of affected b lack fathers could be interpreted as the effect of a sex-linked recess ive modifier gene acting during gametogenesis on an autosomal dominant polydactyly gene, this modifier being more frequent in Africans.