The and Riley-Day syndromes are two of several syndromes associated with self-injurious behavior. Lesch-Nyhan syndrome is caused by a deficiency in the enzyme hypoxanthine guanine phosphoribosyltransferase. The lack of this enzyme is associated with mental retardation and severe self-biting, particularly of the lips, tongue, and fingers.24 The exact mechanisms causing the self-mutilation are poorly understood. Hypotheses range from a problem with pain perception25 to a dynamic interplay between dopamine uptake, serotonin, and the neuronal systems of the basal ganglia.26

Riley-Day syndrome is a disorder of the autonomic nervous system with an autosomal recessive mode of inheritance.27,28 The diagnosis is based on clinical features that include

• absence of tears
• corneal anesthesia
• keratinized conjunctiva and cornea
• insensitivity to pain
• poor temperature control
• abolished deep tendon reflexes
• postural hypotension
• vomiting attacks
• poor motor control
• mental retardation

The disease probably results from an as-yet unidentified enzymatic insufficiency.

Adapted from: Sudhalter V. Problem behaviors in individuals with developmental disabilities. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;165–174.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.