The aim of this work was to study the prevalence at birth and family a
ggregation of polydactyly in Chile. We studied 125.652 newborns betwee
n 1969 and 1991. The prevalence was 1.329 for each 1.000 live newborns
and higher in males than in females. Familial recurrence was 22.5% an
d gene penetrance was estimated as 0.5 for the postaxial-A type and 0.
3 for the postaxial-B type. Gene penetrance for postaxial-B type was h
igher in males. Estimation of gene frequencies and mutation rates gave
the highest values for postaxial-B polydactyly.