Furthermore, in this metabolic pathway, (S)-Methylmalonate semialdehyde could be reversibly converted to L-3-Amino-isobutanoate and Methylmalonate (which were both known AD-related metabolites) by 4-aminobutyrate aminotransferase (ABAT) and aldehyde dehydrogenases (ALDH), respectively. This evidence concerns the gene ABAT and Alzheimer disease.