Lesch Nyhan Syndrome
This disease is caused by the absence or deficiency of an enzyme. Symptoms include impaired kidney function, joint pain and self-mutilating behaviors such as lip and finger biting and/or head-banging. Additional symptoms may include muscle weakness (hypotonia), uncontrolled muscle movements and neurological impairment. Other names for it include HGPRT or HPRT deficiency, or hypoxanthine-guanine phosphoribosyl transferase deficiency.