|Classification and external resources|
Argininosuccinic aciduria, also called argininosuccinic acidemia, is an inherited disorder that causes the accumulation of argininosuccinic acid (also known as "ASA") in the blood and urine. Some patients may also have an elevation of ammonia, a toxic chemical, which can affect the nervous system. Argininosuccinic aciduria may become evident in the first few days of life because of high blood ammonia, or later in life presenting with "sparse" or "brittle" hair, developmental delay, and tremors.
An infant with argininosuccinic aciduria may seem lethargic or be unwilling to eat, have poorly controlled breathing rate or body temperature, experience seizures or unusual body movements, or go into a coma. Complications from argininosuccinic aciduria may include developmental delay and mental retardation. Progressive liver damage, skin lesions, and brittle hair may also be seen. Immediate treatment and lifelong management (following a strict diet and using appropriate supplements) may prevent many of these complications.
Occasionally, an individual may inherit a mild form of the disorder in which ammonia accumulates in the bloodstream only during periods of illness or other stress.
Argininosuccinic aciduria occurs in approximately 1 in 70,000 live births. Many patients can now be detected on the newborn screen if their blood citrulline is elevated.
Mutations in the ASL gene cause argininosuccinic aciduria. Argininosuccinic aciduria belongs to a class of genetic diseases called urea cycle disorders. The urea cycle is a sequence of reactions in the cells of the liver. It processes excess nitrogen, generated when protein is used by the body, to make a compound called urea that is excreted by the kidneys.
In argininosuccinic aciduria, the enzyme argininosuccinate lyase, involved in the conversion of arginino succinate to arginine within the urea cycle, is damaged or missing. The urea cycle cannot proceed normally, and nitrogen accumulates in the bloodstream in the form of ammonia.
Ammonia is especially damaging to the nervous system, so argininosuccinic aciduria causes neurological problems as well as eventual damage to the liver.
This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.
Due to the rarity of the disease, it is hard to estimate mortality rates or life expectancy. One 2003 study which followed 88 cases receiving two different kinds of treatment found that very few persons lived beyond age 20 and none beyond age 30.
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|Urea cycle Metabolic Pathway|