Argininemia

Argininemia is a rare genetic disorder. People with argininemia have problems with an enzyme called arginase I as it is either missing, deficient, or damaged. The arginase I enzyme has an important job as part of the urea cycle and you may hear argininemia referred to as a urea cycle disorder. 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, which is one of the steps of 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.

Unlike most urea cycle disorders, argininemia usually does not cause severe symptoms in infancy. Infants may be irritable, vomit and exhibit feeding problems. They may be less alert when given cow's milk. Some infants may refuse to eat. Argininemia will affect the central nervous system. If untreated, around the age or 3 or 4, children may be clumsy and may fail to gain weight or grow as would be normally expected. They may have delays in reaching developmental milestones and may lose skills that they had already developed. Seizures are common and intellectual disability, tremors, and a condition called spasticity also develop. Spasticity is when there is increased muscle tone and stiffness of leg muscles and can cause muscle spasms.

Unlike the other urea cycle disorders, infants and children with argininemia rarely have what is called a metabolic crisis due to elevated ammonia levels. Ammonia is a neurotoxin that damages central nervous system cells called neurons when there is too much ammonia in the body. In a serious metabolic crisis an infant may vomit, refuse to eat, become increasingly lethargic and eventually end up in coma. A metabolic crisis is a life-threatening complication. In argininemia, ammonia does not build up as much as it does in other urea cycle disorders and an episode of metabolic crisis is rare. When children with argininemia have a metabolic crisis because of elevated ammonia levels, it is usually not as severe and not life-threatening like it is in the other urea cycle disorders, but severe episodes can happen.

Argininemia is caused by a change in a gene called ARG1. The National Urea Cycle Disorders Foundation has more information on argininemia. Some infants who were diagnosed and treatment from birth have remained symptom-free through a special diet and medication. This will also stop symptoms from getting worse if they have already begun. Not all infants and children respond to treatment the same.