Mental retardation and neurological deficits in a twin orangutan.

The second born of a pair of twin orangutans displayed marked behavioral disabilities. To evaluate these disabilities, a series of cognitive, learning, and neurological tests were administered to both twins. The disabled twin showed marked retardation in delayed response and oddity problems and an inability to use tools. The neurological evaluation demonstrated a variety of deficits consistent with damage to the pyramidal motor system. Karyotyping of the twin showed no evidence of chromosomal abnormality. The neurological and behavioral disorders suggested an etiology of perinatal hypoxia. A simple battery of cognitive and neurological tasks is suggested that could be used in evaluating behavioral disabilities in other primates.