Arginase (ARG) Deficiency (also known as hyperargininemia)
Arginase is the last enzyme of the urea cycle that breaks down the amino acid arginine produced by the urea cycle, into two molecules, urea and ornithine. The urea is disposed of by the kidneys; this is the way nitrogen from ammonia is excreted by the body. Arginase deficiency is typically not characterized by severe increase in ammonia. Patients often present with progressive problems of muscle control. They can also develop seizures and have developmental disabilities. Growth is usually slow and without therapy they usually do not reach normal adult height. Other symptoms that may present early in life include episodes of irritability, poor appetite, and vomiting. Severe episodes of hyperammonemia can occur but are infrequent.
The specific diagnosis relies on finding elevated levels of arginine in the blood and by analysis of enzymatic activity in red blood cells and/or DNA analysis for mutations.
Treatment is similar to other urea cycle disorders (except arginine is of course contraindicated), with restriction of protein intake, use of essential amino acid supplements and diversion of nitrogen by alternate pathway therapy with sodium benzoate and/or sodium phenylbutyrate.