GLDC

The GLDC gene provides instructions for making an enzyme called glycine dehydrogenase. This enzyme is one of four components (subunits) that make up a large complex called glycine cleavage enzyme. Within cells, this complex is active in specialized energy-producing centers called mitochondria.

As its name suggests, glycine cleavage enzyme processes a molecule called glycine by cutting (cleaving) it into smaller pieces. Glycine is an amino acid, which is a building block of proteins. This molecule also acts as a neurotransmitter, which is a chemical messenger that transmits signals in the brain. The breakdown of excess glycine is necessary for the normal development and function of nerve cells in the brain and spinal cord.

glycine encephalopathy - caused by mutations in the GLDC gene

Mutations in the GLDC gene account for about 80 percent of all cases of glycine encephalopathy. More than 40 mutations have been identified in affected individuals. Many of these genetic changes alter single amino acids in glycine dehydrogenase. For example, the most common GLDC mutation in the Finnish population replaces the amino acid serine with the amino acid isoleucine at position 564 in the enzyme (also written as Ser564Ile or S564I). Other mutations insert or delete genetic material in the GLDC gene, or disrupt how genetic information from the gene is spliced together to make a blueprint for producing glycine dehydrogenase.

Some GLDC mutations lead to the production of a nonfunctional version of glycine dehydrogenase, while other mutations reduce but do not eliminate the enzyme's activity. When an altered version of this enzyme is incorporated into the glycine cleavage enzyme complex, it prevents the complex from breaking down glycine properly. As a result, excess glycine can build up to toxic levels in the body's organs and tissues. Damage caused by harmful amounts of this molecule in the brain and spinal cord is responsible for the intellectual disability, seizures, and breathing difficulties characteristic of glycine encephalopathy.