Arginase deficiency is an inherited disorder that causes the amino acid arginine (a building block of proteins) and ammonia to accumulate gradually in the blood. Ammonia, which is formed when proteins are broken down in the body, is toxic if levels become too high. The nervous system is especially sensitive to the effects of excess ammonia.

Arginase deficiency usually becomes evident by about the age of 3. It most often appears as stiffness, especially in the legs, caused by abnormal tensing of the muscles (spasticity). Other symptoms may include slower than normal growth, developmental delays and eventual loss of developmental milestones, intellectual disabilities, seizures, tremors, and difficulty with balance and coordination (ataxia). Occasionally, high-protein meals or stress caused by illness or periods without food (fasting) may cause ammonia to accumulate more quickly in the blood. This rapid increase in ammonia may lead to episodes of irritability, refusal to eat, and vomiting.

In some affected individuals, the signs and symptoms of arginase deficiency may be less severe and may not appear until later in life.

Arginase deficiency is a very rare disorder; it has been estimated to occur once in every 300,000 to 1,000,000 individuals.

Arginase deficiency is caused by variants (also called mutations) in the ARG1 gene. This gene provides instructions for making an enzyme called arginase.

Arginase deficiency belongs to a class of genetic diseases called urea cycle disorders. The urea cycle is a sequence of reactions that occurs in liver cells. This cycle processes excess nitrogen, generated when protein is used by the body, to make a compound called urea that is excreted by the kidneys.

The arginase enzyme facilitates the final step of the urea cycle, which produces urea by removing nitrogen from arginine. In people with arginase deficiency, arginase is damaged or missing, and arginine is not broken down properly. As a result, urea cannot be produced normally, and excess nitrogen accumulates in the blood in the form of ammonia. The accumulation of ammonia and arginine are believed to cause the neurological problems and other signs and symptoms of arginase deficiency.

Genetic Testing Information

• Genetic Testing Registry: Arginase deficiency

Genetic and Rare Diseases Information Center

• Argininemia

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Clinical Trials

• ClinicalTrials.gov

Catalog of Genes and Diseases from OMIM

• ARGININEMIA

Scientific Articles on PubMed

• PubMed

• Ah Mew N, Simpson KL, Gropman AL, Lanpher BC, Chapman KA, Summar ML. Urea Cycle Disorders Overview. 2003 Apr 29 [updated 2017 Jun 22]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from http://www.ncbi.nlm.nih.gov/books/NBK1217/ Citation on PubMed
• Crombez EA, Cederbaum SD. Hyperargininemia due to liver arginase deficiency. Mol Genet Metab. 2005 Mar;84(3):243-51. doi: 10.1016/j.ymgme.2004.11.004. Epub 2004 Dec 19. Citation on PubMed
• Endo F, Matsuura T, Yanagita K, Matsuda I. Clinical manifestations of inborn errors of the urea cycle and related metabolic disorders during childhood. J Nutr. 2004 Jun;134(6 Suppl):1605S-1609S; discussion 1630S-1632S, 1667S-1672S. doi: 10.1093/jn/134.6.1605S. Citation on PubMed
• Scaglia F, Brunetti-Pierri N, Kleppe S, Marini J, Carter S, Garlick P, Jahoor F, O'Brien W, Lee B. Clinical consequences of urea cycle enzyme deficiencies and potential links to arginine and nitric oxide metabolism. J Nutr. 2004 Oct;134(10 Suppl):2775S-2782S; discussion 2796S-2797S. doi: 10.1093/jn/134.10.2775S. Citation on PubMed
• Sun A, Crombez EA, Wong D. Arginase Deficiency. 2004 Oct 21 [updated 2020 May 28]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from http://www.ncbi.nlm.nih.gov/books/NBK1159/ Citation on PubMed