Non-ketotic Hyperglycinemia (NKH) more commonly known as Glycine encephalopathy is an autosomal recessive metabolic disorder. Clinical presentation shows abnormally high level of Glycine which is a form of amino acid. This works as a neurotransmitter or chemical messenger in the brain. Primary cause of non-ketotic hyperglycinemia is insufficient amounts of the enzyme which normally metabolizes the amino acid, glycine, in the body. Shortage or lack of this enzyme allows abnormally high levels of glycine to accumulate in the organs and tissues. Particularly affected is the brain which leads to complicated medical problems.

The symptoms of NKH patients depend on the specific form and age of onset. Classic neonatal or Classic forms have symptoms such as lethargy, hypotonia and myoclonic jerks progressing to apnea and oftentimes lead to death. Patients who regain respiration suffer from intractable seizures and mental retardation. Infantile form is associated with seizures and varying degrees of mental retardation following 6 months of normal development. Mild episodic form happens during childhood and is associated with mental retardation, delirium, chorea and vertical gaze palsy during fever. Late onset form occurs during childhood. Symptoms include optic atrophy and spastic diplegia. Atypical form is non-specific. Symptoms include expressive speech deficit and some neurologic abnormalities. Transient form presents as elevated plasma and CSF glycine levels at birth. This is normalized between 2 and 8 weeks.

Genetics play an important role in the development of non-ketotic hyperglycinemia. Mutations in the AMT and GLDC genes are responsible for glycine encephalopathy. 80% of the cases occur as a result of mutations in the GLDC gene. AMT mutations account for 10% to 15% of all reported cases. However, a small percentage of affected individuals have unknown causes.

nonketotichyperglycinemia