In beta-ureidopropionase deficiency, patients accumulate specific metabolites such as of N-carbamyl-β-aminoisobutyric acid, N-carbamyl-β-alanine (also known as 3-ureidopropanoate), uracil, thymine, 5,6-dihydrouracil, and 5,6-dihydrothymine in urine and plasma, leading to variable neurological phenotypes (from asymptomatic to developmental disorder) [25]. The gene discussed is UPB1; the disease is hyperinsulinemic hypoglycemia, familial, 4.