These abnormalities include complete hypoxanthine-guanine phosphoribosyl transferase (HGPRT) deficiency (Lesch–Nyhan syndrome), partial HGPRT deficiency (Kelly–Seegmiller syndrome), adenine phosphoribosyl transferase (APRT) deficiency, phosphoribosyl pyrophosphate (PRPP) synthetase overactivity, and myoadenylate deaminase deficiency. The gene discussed is APRT; the disease is hyperinsulinemic hypoglycemia, familial, 4.