UPB1 and dihydropyrimidine dehydrogenase deficiency: Notably, functional deficiency of pyrimidine pathway genes, such as uridine monophosphate synthase (UMPS), dihydropyrimidine dehydrogenase (DPYD), Dihydropyrimidinase (DPYS), beta-ureidopropionase 1 (UPB1), leads to neurological aberrations, including ASD-like features in case of DPD deficiency (DPYD gene deficiency)55.