A 6-year-old boy with moderate mental retardation is brought to the physician for a follow-up examination. He has had choreoathetoid movements since the age of 16 months. He has been biting his lips and fingers for the past 2 months. His older brother has a similar condition. Physical examination shows spasticity of the lower limbs. Laboratory studies show an increased serum uric acid concentration and an increased urinary excretion of uric acid. His increased serum uric acid concentration is most likely due to which of the following?

Question

Quizplus · Accepted Answer

The symptoms and laboratory findings are consistent with Lesch-Nyhan syndrome, which is caused by a deficiency in hypoxanthine guanine phosphoribosyltransferase (HGPRT) activity. This leads to increased uric acid production. This patient is exhibiting symptoms of Lesch-Nyhan syndrome (LNS). Lesch-Nyhan syndrome is a disorder related to defects in the activity of the purine nucleotide salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRT). The characteristic clinical features of the LNS are mental retardation, spastic cerebral palsy, choreoathetosis, uric acid urinary stones, and selfdestructive biting of fingers and lips. The overall clinical features of LNS can be divided into 3 broad categories: uric acid overproduction and its associated consequences (eg, gouty arthritis and renal lithiasis) neurobehavioral dysfunction indicative of central nervous system involvement, and growth retardation.

A 6-Year-Old Boy with Moderate Mental Retardation Is Brought to the Physician