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An inherited disorder that is associated with X-linked transmission and may be lethal in utero to hemizygous males. Clinically, birth and development in affected females is normal until the age of 6-25 months, when progressive loss of voluntary control of hand movements and communication skills, ataxia, stereotypic hand movements, seizures, autistic behavior, intermittent hyperventilation, and hyperammonemia appear. (From Menkes, Textbook of Child Neurology, 5th ed, p199)