An update on multiplexed mass spectrometry-based lysosomal storage disease diagnosis

Lysosomal storage disorders (LSDs) are a type of inherited metabolic disorders in which biomolecules, accumulate as a specific substrate in lysosomes due to specific individual enzyme deficiencies. Despite the fact that LSDs are incurable, various approaches, including enzyme replacement therapy, hematopoietic stem cell transplantation, or gene therapy are now available. Therefore, a timely diagnosis is a critical initial step in patient treatment. The-state-of-the-art in LSD diagnostic uses, in the first stage, enzymatic activity determination by fluorimetry or by mass spectrometry (MS) with the aid of dry blood spots, based on different enzymatic substrate structures. Due to its sensitivity, high precision, and ability to screen for an unprecedented number of diseases in a single assay, multiplexed tandem MS-based enzyme activity assays for the screening of LSDs in newborns have recently received a lot of attention. Here, (i) we review the current approaches used for simultaneous enzymatic activity determination of LSDs in dried blood spots using multiplex-LC-MS/MS; (ii) we explore the need for designing novel enzymatic substrates that generate different enzymatic products with distinct molecular masses in multiplexed-MS studies; and (iii) we give examples of the relevance of affinity-MS technique as a basis for reversing undesirable immune-reactivity in enzyme replacement therapy.