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). [from
OMIM]