Argininosuccinic aciduria

Causes

What gene changes cause argininosuccinic aciduria?

Argininosuccinic aciduria is caused by gene changes in the ASL gene. People have about 20,000-25,000 genes in their bodies. Our genes contain our body's genetic information, called DNA; genes are segments of DNA found on chromosomes. Genes are inherited from our parents and passed on to our children. Genes are like our body's instruction manual - they control the growth, development and normal function of the body. Genes produce specific proteins that the body needs to grow and work properly. When there is an unexpected change in a gene, the protein that the gene produces may be absent or not work properly or be overproduced. A common type of gene change is a mutation, in which the DNA sequence that makes up a gene is altered. Mutations can be different sizes and can alter a gene in different ways. Sometimes, a mutation can affect multiple genes.

To find a medical professional nearby who can discuss information about gene changes in argininosuccinic aciduria, a listing of medical geneticists can be found at the American College of Medical Genetics and Genomics website and genetic counselors can be found on the National Society of Genetic Counselors website in the United States, and in Canada at the Canadian Association of Genetic Counsellors website.

References
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How does the gene change cause symptoms in argininosuccinic aciduria?

Does anything make argininosuccinic aciduria worse?

How does the gene change cause symptoms in argininosuccinic aciduria?

Argininosuccinic aciduria is caused by a change in a gene called ASL. This gene produces an enzyme known as argininosuccinate lyase. An enzyme is a specialized protein that helps bring about chemical reactions in the body; they act as catalysts. Because of the gene change, people with argininosuccinic aciduria do not produce enough, or produce a damage form of this enzyme. Argininosuccinate lyase has a job. It is involved in the fourth step of the urea cycle. This cycle is series of biochemical reactions that occur in the body to help to break down (metabolize) and then remove excess nitrogen from the body. Nitrogen is obtained from the diet and is a normal waste product of the metabolism of protein. Nitrogen is broken down into a compound called urea that is passed from the body in the urine. People with argininosuccinic aciduria cannot properly break down nitrogen to urea. This causes nitrogen (in the form of ammonia) and other substances to build up in the body.

Ammonia is a neurotoxin, it damages cells of the central nervous system (which is made up of the brain and spinal). When ammonia levels get high enough, this can cause damage to the brain and central nervous system. However, some people with argininosuccinic aciduria develop neurological problems even when their ammonia levels are kept in balance since birth.

This has led researchers to believe that argininosuccinic aciduria is a more complex disorder than they originally thought. The symptoms occur for reasons other than the buildup of ammonia. Researchers are studying the disorder to try and determine these other factors.

References
Does anything make argininosuccinic aciduria worse?

There are several things that can make a urea cycle disorder worse. This is includes eating a lot protein, surgery, having another illness like a viral infection, or certain drugs like valproic acid, which is used to treat seizures. These things create stress on the urea cycle, the series of biochemical steps through which the body breaks down (metabolizes) and removes nitrogen from the body. Nitrogen is obtained from protein in the diet. These things can lead to a buildup of ammonia and other substances in the blood and the body. However, significantly increased ammonia levels can occur and is a life-threatening complication the requires hospitalization.

References

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