Hallux duplication, postaxial polydactyly, absence of the corpus callosum, severe mental retardation, and additional anomalies in two unrelated patients: a new syndrome.

Two unrelated patients, a 4-year-old boy and a 2 1/2-year-old girl, presented with a similar pattern of abnormalities. Both had severe mental retardation, macrocephaly, absence of the corpus callosum, unusual facial appearance, duplication of hallucal phalanges, postaxial hexadactyly of finger phalanges, and 2/3-syndactyly of toes. The boy also had postaxial hexadactyly of toe phalanges, inguinal hernias and umbilical hernia, and growth retardation. We suspect a common cause of this apparently "new" syndrome, most likely a gene mutation.