Crossed polydactyly type I in a mother and son: an autosomal dominant trait?

In a Japanese family, a propositus and his mother had crossed polydactyly type I. A maternal grandaunt also had preaxial polydactyly of the feet. The findings that both of the mother and son had the identical type of polydactyly are consistent with an autosomal dominant inheritance with variable expressivity. Other explanations include X-linked recessive inheritance, polygenic inheritance, and a chance occurrence of the 2 different kinds of polydactyly.