AbstractIntroduction: Lysosomal storage disorders (LSD’s) are a group of more than 40 disorders caused by the specific deficiency of enzymes (& co-factors) within the lysosome. This leads to the accumulation of substrates, lipids, sphingolipids and mucopolysaccharides resulting in organelle and cellular dysfunction and the pathology in the LSD’s. The estimated incidence has been determined to be as high as 1 in 7,000 in the Australian population (1), even higher in certain ethic groups.
Results & Discussion: All 6 LSD, 4 MPS & 1 CLN2 (TPP1) analytical assay performance had acceptable CV% on repeat DBS QC analysis of <12%. The statistical analysis of the normal population gave the 1st centile in IU/hr/L whole blood for each enzyme and was used to assess the activities of the known positive LSD DBS. All LSD & MPS cases had activities below the 1st centile of the respective normal population, GLA showed some overlap, due to the non-enzymatic in-source fragmentation of the substrate, this was specific to the API5000 and not seen on the API3200 or 4000 instruments. Each assay showed >3 orders of magnitude in dynamic range with excellent lower end sensitivity.
Confirmatory high risk screening using MSMS for the determination of metabolites for urine glycosaminoglycans (mono, dioligosaccharides) was performed using 1-phenyl-3-methylpyrazolone (PMP) and plasma for determination of Glycosylsphingosine (lysoGb1 & Lyso Gb3), Lyso-ceramide trihexoside, C18:0-Sulphatide (MLD) and Lyso Sphingomylein 509. These high risk screening markers were used to confirm the low dried blood-spot enzyme activities from the Mult-Plex assays.
Conclusion: The simplicity and accuracy of the PE Multi-plex MSMS LSD reagents makes it amenable for use in both newborn screening and high risk screening. Our study clearly showed the superior performance characteristics of large dynamic range and lower end assay sensitivity that was able to distinguish between unaffected and confirmed true positive LSD cases. The MSMS confirmatory metabolite tests is used to confirm or exclude an LSD.