Lack of evidence of a major gene acting on postaxial polydactyly in South America

Data on polydactyly were obtained from two large samples: the Latin America n Collaborative Study of Congenital Malformations (ECLAMC), and from a migr ant Northeastern Brazilian population of rural origin (Hospedaria). ECLAMC is a case-control clinical epidemiological program comprising 10,035 indivi duals distributed among 2,030 segregating nuclear families, Hospedaria data consisted of 6,586 examined individuals belonging to 1,040 nuclear familie s. Using complex segregation analysis methodology we found no evidence of t wo loci (a major gene and a modifier locus) acting on postaxial polydactyly in the present study. Very high heritability values (in a classical multif actorial model) of postaxial polydactyly were detected, for several sets of analyses in ECLAMC and in Hospedaria, For the whole ECLAMC sample there is a peculiar suggestion of a major recessive gene effect responsible for the trait; however, no comparison with a model involving transmission probabil ities (tau) was possible in this highly heterogeneous sample. If the whole ECLAMC sample is divided in subsamples, according to Black admixture propor tions, the same multifactorial picture emerges. Two different inheritance p atterns were verified for hand (HP) and foot (FP) postaxial polydactyly: Fo r HP there is evidence of a non-Mendelian transmission mechanism, while for FP the parental/sib transmission appears to be due only to multifactorial causes. Am. J, Med, Genet. 80:466-472, 1998, (C) 1998 Wiley-Liss, Inc.