Presentation October 16th 2018

High risk screening of MPS disorders (MSPII,III,IVa...)

Abstract 

Introduction: 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. 

Early identification and treatment (e.g. enzyme replacement, substrate depletion & BMT therapies) reduces the pathology and greatly enhances the quality of life and life expectancy. Therefore newborn screening for LSD’s provides the ability to identify prior to the onset of disease and the commencement of targeted treatment when asymptomatic. Analysis using the Perkinelmer Multi-plex LSD reagents for the determination of 6 LSD (6-Plex) & 6 MPS enzyme activities from a single dried blood-spot (3.2mm) determined by tandem mass spectrometry (MSMS). The determination of confirmatory diagnostic tests using metabolites for the LSD and MPS disorders by MSMS. 

Method: The 6 LSD enzymes were galactocerebrosidase β-galactosidase (GALC; Krabbe disease), acid α-galactosidase A (GLA; Fabry disease), acid sphingomylinase (ASM; Niemann Pick A/B disease), α-iduronidase (IDUA; mucopolysaccharidosis type I) and β-glucocerbrosidase (ABG; Gaucher disease). The 6 MPS disorders of mucopolysaccharidosis type II, IIIB, IVA, VI VII & TPP1 (CLN2). De-identified newborn dried blood-spots (DBS) were sourced from the South Australian population (~1,000) and DBS from confirmed positive LSD cases (N=75) obtained from the National Referral Laboratory (NRL) that included GALC (5), GLA (14) & carriers (28), ASM A/B (1), IDUA (6), GAA (20) and ABG (20). In addition MPSII (3, Hunter), MPS IIIB (2, Sanfilippo B), MPS IVA (3, Morquio A), MPS VI (2, Maroteaux-Lamy) and TPP1 (2, CLN2). The PE LSD & MPS reagents were obtained from Perkinelmer (Waltham, MA, USA) for research use only. Individual LSD enzyme activities were determined by stable isotope dilution technique by MRM after a single organic solvent extraction and determination by FIA on an API5000 MSMS. MSMS setting were, IS voltage 5000, DP 95, CE 55 & CXP 15. 

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.

The presentations are available for educational exchange purposes only. Products mentioned in the presentation may not be available in your country. Please consult your local PerkinElmer representative for the products available in your country
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