Arginase Deficiency

Here you’ll find answers to some of the questions that parents often have about this condition. More resources are listed at the bottom of the page. More detailed information, aimed at primary care clinicians, can be found in the Arginase Deficiency and the Arginase Deficiency screening page.

Arginase deficiency is a rare genetic disorder. It results from the absence of the enzyme arginase 1, which causes ammonia to build up in the body. While the high levels of ammonia are often mild, they can be life-threatening. If untreated, developmental problems and seizures can happen.

Infants and young children with arginase deficiency usually seem normal until age 1-4 when they start to show muscle tightness and developmental delay. Many also have microcephaly (small head due to poor brain growth).

Newborn screening programs test for arginase deficiency, making diagnosis possible very early in the child's life, before symptoms begin. Testing can also be done if arginase deficiency is suspected in older children.

With treatment, the chance for a normal life is excellent, though it is not yet known whether adults with this condition will be problem-free.

Arginase deficiency is passed down by a child’s parents when they are both carriers of an abnormal gene for the arginase 1 enzyme. When people have just one such gene, they are called carriers and they don’t have the condition. However, people with two abnormal genes will have it. Because everyone has two copies of all of their genes, one from each parent, the chance that a child of parents who are both carriers will have arginase deficiency are 1 in 4.

Treatment involves restricting protein in the diet, taking some essential amino acids, and the use of medications to remove ammonia.

Your child will need to be on a protein-restricted food plan and take amino acids for the rest of her/his life. Some children may also need to take medication. By following treatment, it is thought that most people will lead a normal life.