Hypothesis: one cause of polydactyly.

The strongly male-biased sex ratios of probands with polydactyly and of their unaffected sibs suggests that abnormal maternal hormone levels may be involved in this malformation. This suspicion is supported by data relating polydactyly to maternal age and race. High maternal testosterone seems capable of explaining the (admittedly limited) epidemiological data on polydactyly. If this were so, one may predict that offspring risk would be higher in respect of affected mothers than affected fathers.