Succinic semialdehyde

Succinic semialdehyde (SSA) is a GABA and GHB metabolite. It is formed from GABA by the action of GABA transaminase (4-aminobutyrate aminotransferase) and further oxidised to become succinic acid, which enters TCA cycle. SSA is oxidized into succinic acid by the enzyme succinic semialdehyde dehydrogenase, which uses NAD+ as a cofactor. When the oxidation of succinic semialdehyde to succinic acid is impaired, accumulation of succinic semialdehyde takes place which leads to succinic semialdehyde dehydrogenase deficiency.

In addition to the pathway involving GABA transaminase, gamma-hydroxybutyric acid (GHB) can also be metabolized to SSA via GHB dehydrogenase or by GHB transhydrogenase (D-2-hydroxyglutarate transhydrogenase).