glycine encephalopathy

a genetically heterogeneous, autosomal recessive aminoacidopathy caused by mutations that result in defects in enzymes of the glycine cleavage system, characterized by accumulation of glycine in body fluids, particularly the blood, urine, and cerebrospinal fluid. The neonatal form is the most common, with lethargy, absence of cerebral development, seizures, myoclonic jerks, and frequently coma and respiratory failure. Infantile and late-onset forms are milder. A transient form resembles the neonatal form, with glycine levels normalizing by 8 weeks of age; usually there are no neurologic deficits, although mild mental retardation sometimes occurs. Called also nonketotic hyperglycinemia.