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.

[2] [3]  When the oxidation of succinic semialdehyde to succinic acid is impaired, accumulation of succinic semialdehyde takes place which leads to succinic semialdehyde dehydrogenase deficiency.

[3] 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).