Type : Phenotype or locus, molecular basis unknown;
Description : Microcephaly strictly means abnormally small head size, but usually refers to an occipitofrontal
head circumference below -2 SD from the mean for the infant's gestational age, sex,
and ethnic origin. Microcephaly may appear as an isolated trait or in association
with other malformations. It may also be sporadic or familial. Some familial cases
are autosomal dominant, but most appear to be recessive (see 251200) (summary by Merlob
et al., 1988).;