Quantitative Determination of Branched-Chain Amino Acids in Dried Blood Spot Samples by LC-MSMS and its Application in Diagnosis and Follow-Up of Chilean Patients with Maple Syrup Urine Disease

Abstract

Elevation of branched-chain amino acids (BCAAs) in biological fluids indicates a deficiency in the branched-chain ketoacid dehydrogenase complex, which causes maple syrup urine disease (MSUD). Detection of increased levels of alloisoleucine confirms the diagnosis, while routine monitoring of leucine concentration is crucial for preventing metabolic decompensation and neurological dysfunction. In the metabolic center at Universidad de Chile, we have confirmed and monitored more than fifty MSUD patients in the last 20 years. Most diagnoses were made by clinical and sibling diagnosis, as MSUD is not included in the Chilean national newborn screening program. Shortening diagnosis time has a fundamental impact on the outcome of patients, therefore we focused on implementing detection of BCAAs in dried blood spot by liquid chromatography mass spectrometry (LC-MSMS) for disease confirmation as well as for biochemical monitoring. Retrospective analysis of samples from 9 diagnosed MSUD patients were performed; BCAAs values were determined via MSMS and LC-MSMS conducted in parallel. Leucine and alloisoleucine levels were positively correlated with patient’s diagnosis age. Alloisoleucine was significatively elevated as early as 24 hr after birth. A predictable variation in BCAAs levels after nutritional intervention among diagnosed MSUD patients was found.

Keywords
Maple syrup urine disease; second tier test; alloisoleucine; newborn screening