Genetics[ edit ] 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.
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Causes Mutations in the ASL gene cause argininosuccinic aciduria. This condition belongs to a class of genetic diseases called urea cycle disorders because they are caused by problems with a process in the body called the urea cycle. The urea cycle is a sequence of reactions that occurs in liver cells. This cycle breaks down excess nitrogen, which is made when protein is used by the body, to make a compound called urea. Urea is removed from the body in urine.
Breaking down excess nitrogen and excreting it as urea prevents it from accumulating in the body as ammonia. The ASL gene provides instructions for making an enzyme called argininosuccinate lyase, which is needed for the fourth step of the urea cycle. The specific role of the argininosuccinate lyase enzyme is to start the reaction in which the amino acid arginine, a building block of proteins, is produced from argininosuccinate, the molecule that carries the waste nitrogen collected earlier in the urea cycle.
The arginine is later broken down into urea, which is excreted, and ornithine, which restarts the urea cycle. In people with argininosuccinic aciduria, argininosuccinate lyase is dysfunctional or missing. As a result, the urea cycle cannot proceed normally, arginine is not produced, and nitrogen is not broken down efficiently. The excess nitrogen accumulates in the blood in the form of ammonia. This buildup of ammonia damages the brain and other tissues and causes neurological problems and other signs and symptoms of argininosuccinic aciduria.
It is unclear how a lack of arginine contributes to the features of this condition.