Lesch-Nyhan syndrome (LNS), also known as Nyhan’s syndrome. Lesch-Nyhan syndrome (LNS) is a rare genetic disorder characterized by an overproduction of uric acid, neurological disability, and behavioral problems. Abnormal involuntary muscle movements such as flexing, jerking, and flailing are often displayed by people affected with this disorder. Self-injury can start as young as two years of age. Self-injury can start as late as 10 or 12 years of age. Some boys with Lesch-Nyhan disease never become self-injurious. People with Lesch-Nyhan syndrome usually cannot walk, need assistance sitting, and are generally wheelchair-bound.
Lesch Nyhan syndrome is caused by a mutation in the HPRT gene on the X-chromosome, resulting in a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase. The gene is recessive and occurs on the X chromosome. Therefore only boys exhibit the disease. Girls are carriers. HPRT is involved in the recycling of purines. Hyperuricemia can result in gouty arthritis, tophi and kidney stones. This condition occurs with a similar frequency in all populations. Frequently the first symptom is the presence of orange-colored crystal-like deposits (orange sand) in the diapers of affected infants.
The deposits, which are called urate crystal formation, are caused by increased levels of uric acid in the urine. Extra symptoms of LNS may comprise kidney stones, blood in the urine, soreness and swelling of the joints, difficulty swallowing (dysphagia) and eating, and vomiting, impaired kidney function, irritability, uncontrolled aggressive and/or compulsive actions, muscle weakness (hypotonia), uncontrolled spastic muscle movements, and neurological problems such as involuntary writhing movements of the arms and legs (athetosis) and purposeless repetitive movements such as shoulder raising and lowering and/or facial grimacing.
Moderate mental retardation is also common. Some individuals may develop a rare disorder called megaloblastic anemia. Treatment for Lesch Nyhan syndrome is symptomatic. Some symptoms may be alleviating with the drugs carbidopa/levodopa, diazepam, phenobarbital, or haloperidol. Management of the behavioral problems, and particularly the self-injurious behavior, can be very difficult. Behavioral extinction methods with positive reinforcement are most beneficial; techniques involving negative reinforcement are not helpful and may even exacerbate the behavior problems.
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