Holoprosencephaly in a Down syndrome child.

Gross malformation of the central nervous system (CNS) is rare in Down syndrome (DS). To our knowledge we report for the first time the association of trisomy 21 and holoprosencephaly. Because of the low probability of chance concurrence due to unrelated causes, a causal relationship between these two conditions in the patient must be presumed. The anatomic similarity of the holoprosencephalic defect in this infant to that seen in others with autosomal dominant, recessive, sporadic, or syndromal forms of holoprosencephaly, supports the hypothesis that: a) this CNS defect is a causally nonspecific developmental field complex (DFC); b) the increased incidence of such DFC's in the DS represents the result of a nonspecific decrease of developmental homeostasis [Waddington, 1975] due to autosomal aneuploidy.