Chromatographic diagnosis of maple syrup urine disease by measuring the l-alloisoleucine/l-phenylalanine ratio in dried blood spots

A high-performance ligand-exchange chromatography with ultraviolet detection method for confirmation diagnosis of maple syrup urine disease (MSUD) was developed that relies on the determination of branched-chain amino acids (BCAAs) and Phe levels in blood. The dynamic ranges for the BCAAs and Phe were 50–1000 μM (r2 = 0.9982–0.9996) and 74–873 μM (r2 = 0.9992) from a dried blood spot, and the BCAA detection limits (S/N = 3) were 0.43–1.91 μM. The mean recoveries of BCAA for intra- and inter-day assays were 92.1–103.0%. The ranges of alloisoleucine (Allo-Ile)/Phe ratio were ND–0.04 and 1.5–2.4 for PKU and MSUD patient samples, respectively. The lowest ratio (1.5) of the MSUD samples was 37.5 times higher than the highest ratio (0.04) of the PKU samples. Therefore, the Allo-Ile/Phe ratio was very useful biomarker for confirmation diagnosis of MSUD.