External quality assurance programme for enzymatic analysis of lysosomal storage diseases: A pilot study

• DOI: 10.1007/s10545-005-0201-z
• Publication Date: 2006-01-25T09:35:29Z
• Authors: G. J. G. Ruijter; M. Boer; C. W. Weykamp; R. De Vries; I. van den Berg; J. Janssens‐Puister; K. Niezen‐Koning; R. A. Wevers; B. J. H. M. Poort...; O. P. van Diggelen
• Keywords: Quality Control; 0301 basic medicine; DCN 1: Perception and Action; Time Factors; DCN 2: Functional Neurogenomics; Pilot Projects; DIAGNOSIS; MANNOSIDOSIS; UMCN 5.1: Genetic defects of metabolism; Specimen Handling; HETEROZYGOTES; 03 medical and health sciences; IGMD 3: Genomic disorders and inherited multi-system disorders; SUBSTRATE; DCN 3: Neuroinformatics; Leukocytes; Humans; LYMPHOID-CELL LINES; ASSAY; EMC MGC-02-96-01; IGMD 4: Glycostation disorders; ARYLSULPHATASE-A; Clinical Laboratory Techniques; Glycogen Storage Disease Type II; Temperature; Reproducibility of Results; ORGANIC-ACID ANALYSIS; beta-Galactosidase; 16. Peace & justice; LEUKOCYTES; 3. Good health; DEFICIENCY; Lysosomal Storage Diseases; Blood; alpha-Galactosidase; NCMLS 4: Energy and redox metabolism; UMCN 3.1: Neuromuscular development and genetic disorders; Lysosomes

AbstractInborn errors of metabolism are rare and laboratories performing diagnostic tests in this field must participate in external quality assurance (EQA) schemes to demonstrate their competence and also to maintain sufficient experience with patient material. EQA schemes for metabolite analyses are available (ERNDIM), but corresponding EQA schemes for enzyme analyses are nonexistent. In this paper we describe a pilot study on lysosomal enzyme testing by four centres in The Netherlands. Quantitative aspects of EQA were studied by interlaboratory comparison of activities of six lysosomal enzymes in a series of buffy coat samples. Interlaboratory variance was enormous. To reduce variance caused by methodological differences, participants reported enzyme activities relative to mean normal values. β‐D‐Galactosidase activities compared well between the participating laboratories (average interlaboratory CV 13%), but for other enzymes large differences were observed, e.g. sphingomyelinase (average CV 38%). Diagnostic proficiency was tested with cultured fibroblasts. In 45 out of a total of 48 tests (12 cell lines, 4 participants) the correct diagnosis was accomplished on the basis of merely biochemical investigations, i.e. without clinical data of the patients. In a survey using blood of a late‐onset Pompe disease patient, less conclusive results were obtained. A stable enzyme source was developed for easy distribution. Most lysosomal enzymes were stable upon lyophilization of leukocyte homogenates and during subsequent storage of the freeze‐dried material at room temperature, in particular when cryolyoprotectant was added. Shipment of such lyophilized samples is simple and cheap and ideal for an EQA scheme. Our study shows that an EQA programme for enzymatic testing of lysosomal storage diseases is necessary to accomplish reliable diagnostic procedures for lysosomal storage diseases. We recommend that EQA for lysosomal enzymes be implemented through ERNDIM.