Lesch-Nyhan syndrome is a genetic disorder associated with overproduction of uric acid, neurological disability, and behavioral problems. The overproduction of uric acid is associated with hyperuricemia. If left untreated, it can produce nephrolithiasis with renal failure, gouty arthritis, and solid subcutaneous deposits known as tophi. The neurological disability encompasses a spectrum of extrapyramidal signs, including dystonia, choreoathetosis, and occasionally ballismus. Some patients also develop pyramidal signs, such as spasticity and hyperreflexia. The behavioral problems include cognitive dysfunction and aggressive and impulsive behaviors. Nearly all patients also develop persistent and severe self-injurious behavior.

The pathogenesis of the neurological and behavioral features is incompletely understood. Neurochemical and neuroimaging studies have demonstrated significant abnormalities of dopamine neuron function in the basal ganglia that might account for the abnormal extrapyramidal neurological signs and many of the behavioral anomalies.