Lesch-Nyhan症候群の1例

抄録

Lesch-Nyhan syndrome is a rare inborn error of purine metabolism. The incidence of this syndrome is about 1/380, 000 live births. The genetic analysis indicates that the disorder had an X-linked recessive pattern. The syndrome is clinically characterized by mental retardation, neurological disorder, self-mutilation, and hyperuricemia. Patients with this syndrome are lacking in purine salvage enzyme (HGPRT). The deficiency of this enzyme leads to excessive production of uric acid. In this paper, a case of this syndrome is described.
A 2-year 11-month-old Japanese boy was referred for evaluation and treatment of lower lip self-biting. The child was born of a normal pregnancy and delivery. He had no neonatal complications. But his pediatrician noticed that his development was retarded physically and mentally. So, laboratory examinations were conducted. Diagnosis of Lesch-Nyhan syndrome including loss of HGPRT activity was made based on the clinical and laboratory findings. Then, treatment with allopuriol was initiated. At the age of 2, he started finger biting. Arm splints were used to reduce this self-mutilative behavior. Besides, he began chewing on his lower lip and repeatedly bit the lip causing soft tissue destruction and ulceration. His appearance had extrapyramidal signs. Fingers of both hands were mutilated and scarred. Oral examination showed the lower lip denuded with ulceration. Under local anesthesia, both deciduous central and lateral incisors were removed to prevent further lower lip tissue loss. The ulcer was healed as scarring.
Self-mutilation is one of the most characteristic symptoms of Lesch-Nyhan syndrome. It usually starts at the age of 2. The patients compulsively bite their fingers and/or lips. Such behavior sometimes lead to extensive soft tissue destruction. However, their sensation is intact and they actually feel pain. The self-mutilation mechanism is still unknown. The behavior does not correlate with the level of uric acid and control of hyperuricemia has no favorable effect on it. Treatment of the patient from neonatal period with allopurinol cannot prevent the onset of the disease, but it can control excessive uric acid production. Physical restraints are usually used to keep patients from injury. Once patients begin to bite themselves, removal of the teeth is practically indicated.