Argininosuccinic aciduria

Argininosuccinic aciduria, also called argininosuccinic acidemia, is an inherited disorder that causes ammonia to accumulate in the blood and urine. Ammonia is toxic, especially to the nervous system, and argininosuccinic aciduria usually becomes evident in the first few days of life.

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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.

Prevalence

Argininosuccinic aciduria occurs in approximately 1 in 70,000 live births.

Genetics

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 that starts a specific reaction 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.

References

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• Lee B, Goss J (2001). "Long-term correction of urea cycle disorders". J Pediatr 138 (1 Suppl): S62-71. PMID 11148551
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• Scaglia F, Brunetti-Pierri N, Kleppe S, Marini J, Carter S, Garlick P, Jahoor F, O'Brien W, Lee B (2004). "Clinical consequences of urea cycle enzyme deficiencies and potential links to arginine and nitric oxide metabolism". J Nutr 134 (10 Suppl): 2775S-2782S; discussion 2796S-2797S. PMID 15465784 Full text
• Stadler S, Gempel K, Bieger I, Pontz BF, Gerbitz KD, Bauer MF, Hofmann S (2001). "Detection of neonatal argininosuccinate lyase deficiency by serum tandem mass spectrometry". J Inherit Metab Dis 24 (3): 370-8. PMID 11486903
• Wilcken B, Smith A, Brown DA (1980). "Urine screening for aminoacidopathies: is it beneficial? Results of a long-term follow-up of cases detected bny screening one million babies". J Pediatr 97 (3): 492-7. PMID 7411317