XK aprosencephaly and anencephaly in sibs.

Recent studies have suggested a causal and pathogenetic relationship between holoprosencephaly and anencephaly. In support of the proposed relationship we report a sibship that includes anencephalic male twins and a female infant with a severe form of alobar holoprosencephaly, radial aplasia, and oligodactyly. The upper limb and brain malformations are considered to represent aprosencephaly syndrome. The coexistence of anencephaly and aprosencephaly within a sibship suggests that XK aprosencephaly syndrome may be an autosomal recessive disorder.