Argininemia

Causes

What gene changes cause argininemia?

Argininemia is caused by gene changes in the ARG1 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.

To find a medical professional nearby who can discuss information about gene changes in the ARG1 gene and argininemia, a listing of medical geneticists can be found at the American College of Medical Geneticists website and genetic counselors can be found on the National Society of Genetic Counselors website.

References
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How does the gene change cause symptoms in argininemia?

Does anything make argininemia worse?

How does the gene change cause symptoms in argininemia?

Argininemia is caused by a change in a gene called ARG1. This gene produces an enzyme known as arginase I. Because of the gene change, people with argininemia do not produce enough, or produce a damage form of this enzyme. Arginase I has a job. It is involved in the last 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 excreted from the body in the urine. People with argininemia cannot properly break down the amino acid arginine, one step of the urea cycle. An amino acid is a building block of protein. Because they cannot break down arginine and cannot completely convert nitrogen into urea, arginine and nitrogen (in the form of ammonia) 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 cord). Ammonia does not build up in argininemia as much as it does in other urea cycle disorders. People with argininemia rarely have a severe metabolic crisis that is common in other urea cycle disorders. During a metabolic crisis, an infant may vomit, refuse to eat, become increasingly lethargic, and eventually end up in coma. A metabolic crisis is considered a life-threatening complication.

Doctors do not understand exactly why symptoms develop in argininemia. Unlike other urea cycle disorders, they do not believe that ammonia plays a big role in the develop of symptoms. Ammonia is not elevated in the same amount as it is in other urea cycle disorders. Doctors know that, if untreated, the persistently elevated levels of arginine and its metabolites (substances formed during metabolism) in the body and the blood most likely play significant roles. Doctors are still trying to determine how a deficiency of the arginase I enzyme causes the symptoms of argininemia

References
Does anything make argininemia worse?

There are several things that can make a urea cycle disorder worse. These include eating a lot protein in the diet, undergoing a surgical procedure, having another illness like a viral infection, or the use of certain drugs like valproic acid, which is used to treat seizures. These 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. The factors describe can lead to a buildup of ammonia and arginine and its metabolites (normal byproducts of metabolism) in the blood and the body. A woman's menstrual cycle is also believed to contribute to elevated levels of ammonia in argininemia. Most times, people with argininemia do not have significantly elevated levels of ammonia in the body and can be treated with intravenous fluids. However, significantly increased ammonia levels can occur and is a life-threatening complication the requires hospitalization.

References

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