Segregation frequency in microcephaly.

A total of 118 cases of microcephaly were clinically evaluated under two main groups: primary microcephaly (61 cases) and secondary microcephaly (57 cases). Secondary cases were generally characterized by convulsions, spasticity, and other congenital anomalies. Estimates of segregation frequency obtained separately in primary and secondary cases indicated that the primary consanguineous cases were most probably due to a single recessive gene. The segregation frequency was substantially less in other types, indicating much lower genetic risks in these cases.