Catalyzes one step in the degradation of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). H2O + NAD(+) + succinate semialdehyde = 2 H(+) + NADH + succinate Redox-regulated. Inhibited under oxydizing conditions. Inhibited by hydrogen peroxide H(2)O(2). Amino-acid degradation; 4-aminobutanoate degradation. Homotetramer. Brain, pancreas, heart, liver, skeletal muscle and kidney. Lower in placenta. The disease is caused by variants affecting the gene represented in this entry. Belongs to the aldehyde dehydrogenase family.