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. Author manuscript; available in PMC: 2017 Oct 1.
Published in final edited form as: Neurochem Int. 2016 Jun 14;99:72–84. doi: 10.1016/j.neuint.2016.06.009

Fig. 2. GABA metabolism and SSADHD.

Fig. 2

GABA normally interconverts to succinic semialdehyde via GABA-transaminase (GABA-T) activity, and subsequently forms succinic acid via succinic semialdehyde dehydrogenase (SSADH), the defect in SSADH deficiency (SSADHD; cross-hatched box). Gamma-hydroxybutyrate (GHB; whose formation is catalyzed by aldo-keto reductase 7a2, AKR7a2), D-2-hydroxyglutaric acid (D-2-HG; the formation of which is catalyzed by nicotinamide-independent D-2-hydroxyglutaric transhydrogenase (TH)), SSA and 4,5-dihydroxyhexanoic acid (DHHA; possibly derived from SSA condensation with an “activated” two carbon species, but unproven) are increased in patient body fluids. Monoamine oxidase (MAO) and β-alanine aminotransferase (βAAT) can also metabolize GABA.