Hyperglycinemia, isolated nonketotic

Overview

Type of disease: Rare conditions

Nonketotic hyperglycinemia is a condition in which there is too much of the amino acid glycine in the body. Amino acids are the building blocks that make up proteins, which help your body perform all of its functions. Glycine usually helps send signals within the brain. In this condition, the protein that breaks down glycine does not work the way it should, so there is a buildup of glycine in the brain.

Nonketotic hyperglycinemia is a genetic condition caused by a change in one of three genes: AMT, GLDC, or GCSH. This condition is passed down from parent to child in an autosomal recessive manner, which means one mutation (changed gene) from each parent is inherited in order to cause symptoms. A person with only one mutation is called a carrier because they “carry” one changed copy of the gene. Carriers usually show no signs or symptoms of the condition. If both parents are carriers, each of their children has a one in four chance (25%) of having the condition and a 50/50 chance of being a carrier.

Symptoms of nonketotic hyperglycinemia usually appear during infancy or early childhood. Symptoms include a lack of energy, problems feeding, low muscle tone, jerking movements, trouble breathing, seizures, and intellectual disability. Doctors can diagnose this by looking at levels of glycine in the blood, brain, and spinal fluid, looking at images of the brain, and evaluating development. Individual symptoms of the condition, like seizures and swallowing problems, can be treated. Medications may also be used to lower the levels of glycine in the blood. The outcome for individuals with nonketotic hyperglycinemia varies depending on how severe the symptoms are. Usually, patients that develop the condition right after birth or as infants have severe outcomes.

If you or a family member has been diagnosed with nonketotic hyperglycinemia, talk with your doctor about the most current treatment options.

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