APA Dictionary of Psychology

a congenital disorder in which microcephaly is the primary, and usually the only, evidence of anomalous fetal development. The most common characteristic is an average-size face combined with a small cranium. The forehead is low and narrow but recedes sharply. The back of the head is flat, and the vertex often is pointed. Intellectual developmental disorder and spasticity of limbs occur as neurological deficits.