Is anencephaly a single entity? A brief note on the morphologic heterogeneity of anencephaly.

Considerations of the genetics of anencephaly have been based on the premise that this dysraphism is a single entity. However, morphologically anencephaly is a heterogeneous group made up of at least four major morphologic types-anencephalus craniorachischisis, anencephalus acrania, microcephalus acrania and microcephalus craniorachischisis. While I believe that the various types of anencephaly represent only degrees of severity of the same basic underlying defect(s), the possiblity of genetic as well as morphologic heterogeneity should be considered.