Lesch-Nyhan variant syndrome: variable presentation in 3 affected family members.

Background: Lesch-Nyhan disease is an inborn error of purine metabolism that results from deficiency of the activity of hypoxanthine phosphoribosyltransferase (HPRT). The heterogeneity of clinical phenotypes seen in HPRT deficiency corresponds to an inverse relationship between HPRT enzyme activity and clinical severity. With rare exception, each mutation produces a stereotypical pattern of clinical disease; onset of neurologic symptoms occurs during infancy and is thought to be nonprogressive.