Gamma-Aminobutyric Acid Transaminase Deficiency

Gamma-aminobutyric acid transaminase (GABA-T) deficiency is an extremely rare disorder of GABA metabolism characterized by a severe neonatal-infantile epileptic encephalopathy (manifesting with symptoms such as seizures, hypotonia, hyperreflexia and developmental delay) and growth acceleration.

Epidemiology

Five patients from three affected families have been reported in the literature to date.

Clinical description

Onset occurs in the neonatal/infantile period. Manifestations reported include hypotonia, impaired psychomotor development, hyperreflexia, lethargy, seizures, high-pitched cry, accelerated linear growth and developmental delay. The phenotype of GABA-T deficiency is more severe than what is seen in succinic semialdehyde dehydrogenase (SSADH) deficiency (see this term), although some patients have survived infancy but with severe neurodevelopmental impairment including myoclonic seizures and choreoathetosis.

Etiology

GABA-T deficiency is caused by a mutation in the ABAT gene (16p13.2) encoding mitochondrial 4-aminobutyrate aminotransferase (GABA-T). GABA-T is responsible for catalyzing the conversion of gamma-aminobutyrate to succinate semialdehyde in the GABA metabolic pathway. A mutation in this gene leads to an increased accumulation of GABA in central nervous tissue, leading to encephalopathy.

Genetic counseling

GABA-T deficiency is inherited in an autosomal recessive manner.