Glycine Encephalopathy (GCE), also known as nonketotic hyperglycinemia, is an autosomal recessive defect of glycine metabolism, characterized by an accumulation of the amino acid in body tissues, especially in the brain. The classical form of GCE manifests itself soon after birth and is typified by hypotonia, feeding and breathing difficulties, and lethargy. The condition can be fatal at this stage, if not properly managed. Infant who do survive, develop further complications, including mental retardation and recalcitrant seizures. Apart from the classical form, other atypical forms of GCE also exist. These include the infantile form, which presents itself only about six months after birth, as well as childhood or adult-onset forms. In general, the later the onset, the milder are the symptoms. Another rare variant of the disease is the transient neonatal form, which presents as a typical case of classical GCE at birth. However, the glycine levels in this case, return to normal with time and, usually, no long-term complications remain.
Infants who present with the above-mentioned symptoms along with elevated glycine levels are suspected to have GCE. An increased CSF:plasma concentration of glycine is a strong indicator of the condition. Confirmation is, however, done only on the basis of molecular genetic testing of mutations in either the GLDC, AMT, or GCSH genes. Management of the disease is difficult. Standard anticonvulsant drugs cannot be administered, since they either tend to raise the glycine levels, or have only limited efficacy in controlling the seizures. Instead, benzoate is recommended. No treatment is available for GCE.