Genetic microcephaly in a pair of monozygous twins.

A pair of monozygotic female twins with true primary microcephaly is described. The autosomal-recessive nature of the disease is supported by the following: the twins are concordant for the disease; the parents, themselves normal, are related; the reduced skull dimensions were noted at birth; neurologic problems are absent; the karyotype is normal; the gestation and delivery were normal, without any history of influences capable of inducing microcephaly. A detailed dermatoglyphic study is given.