We undertook a retrospective review of plasma BCAA levels in individuals with UCDs comprising ornithine carbamoyltransferase deficiency (OTCD n = 22), arginosuccinate lyase deficiency (ASLD n = 12), and argininosuccinate synthase deficiency (ASSD n = 6). The gene discussed is ASS1; the disease is ornithine carbamoyltransferase deficiency.