LESCH-NYHAN SYNDROME (X-LINKED RECESSIVE DISORDERS SERIES 1)
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Lesch-Nyhan syndrome is a condition that occurs almost exclusively in males. It is characterized by neurological and behavioural abnormalities and the overproduction of uric acid. Uric acid accumulation can also cause kidney and bladder stones. The prevalence of Lesch-Nyhan syndrome is approximately 1 in 380,000 individuals. This condition occurs with a similar frequency in all populations.
SIGNS AND SYMPTOMS
The symptoms of Lesch-Nyhan syndrome may become apparent as early as six months of age. Earlier urate crystal formation, resulting from abnormally increased uric acid levels in the urine, leads to the presence of orange-coloured deposits in the diapers of infants with this disorder. This may be the first manifestation of Lesch-Nyhan syndrome, but it is seldom recognized in early infancy.
In older children with this disorder, deposits of sodium urate in cartilaginous tissues in joints and the ears; in the ears, they form visible bulges called tophi. This is the picture commonly known as gout.
Neurological symptoms associated with Lesch-Nyhan syndrome usually begin before the age of 12 months. People with this syndrome experience nervous system-related issues. The nervous system and behavioural disturbances experienced by people with Lesch-Nyhan syndrome include Abnormal involuntary muscle movements, Tensing of various muscles (dystonia), Jerking movements (chorea) and Eratical movement of the limbs (ballismus).
The most striking feature of Lesch-Nyhan syndrome, which has been observed in approximately 85 per cent of patients, is Self-injurious behaviour, which may include repeated biting of the lips, fingers, and/or hands, and repetitive banging of the head against hard objects. Some children may scratch their faces repeatedly. However, individuals with Lesch-Nyhan syndrome are not insensitive to pain. Additional behavioural abnormalities include aggressiveness, vomiting, and spitting. Self-injurious behaviours regularly lead to loss of tissue.
CAUSES
Mutations in the HPRT1 gene cause Lesch-Nyhan syndrome. The HPRT1 gene provides instructions for making an enzyme called hypoxanthine phosphoribosyltransferase 1. This enzyme is responsible for recycling purines. HPRT1 gene mutations that cause Lesch-Nyhan syndrome result in a severe shortage (deficiency) or complete absence of hypoxanthine phosphoribosyltransferase 1. When this enzyme is lacking, purines are broken down but not recycled, producing abnormally high levels of uric acid. Some people with HPRT1 gene mutations produce some functional enzymes. These individuals are said to have the Lesch-Nyhan variant. The signs and symptoms of the Lesch-Nyhan variant are often milder than those of Lesch-Nyhan syndrome and do not include self-injury.
DIAGNOSIS
The diagnosis of Lesch-Nyhan syndrome may be confirmed by a thorough clinical evaluation, including a detailed patient history and specialized blood tests. Molecular genetic testing for the HPRT1 gene is available to determine the specific disease-causing mutation. Carrier testing for Lesch-Nyhan syndrome is possible using molecular genetic testing.
TREATMENT
The treatment of Lesch-Nyhan syndrome is directed toward the specific symptoms that are apparent in each individual.
The drug allopurinol is used to control the excessive amounts of uric acid associated with Lesch-Nyhan syndrome and control symptoms associated with excessive amounts of uric acid.
When kidney stones are present, they may be treated with extracorporeal shock wave lithotripsy (ESWL).
No sustained treatment or drug therapy has proven uniformly effective for the treatment of the neurological problems associated with Lesch-Nyhan syndrome. Baclofen or benzodiazepines have been used to treat spasticity. Diazepam may be useful.
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