(1)
Lysosomal storage diseases are rare inherited disorders with no standardized or commercially available tests for biochemical diagnosis. We present factors influencing the quality of
enzyme assays for
metachromatic leukodystrophy (MLD) and
gangliosidoses (GM1; GM2 variants B and 0) and validate the reliability and stability of testing in a retrospective analysis of 725 samples. (2) Patient leukocytes were isolated from
ethylene-
diamine-tetra-
acetic acid (
EDTA) blood and separated for subpopulation experiments using density gradient centrifugation or magnetic cell separation.
Enzyme activities in whole leukocyte lysate and leukocyte subpopulations were determined. (3) The
enzyme activities in leukocyte subpopulations differed significantly. Compared to lymphocytes, the respective
enzyme activities were 2.31-4.57-fold higher in monocytes and 1.64-2.81-fold higher in granulocytes. During sample preparation, a considerable amount of the lysosomal
enzymes was released from granulocytes. Nevertheless, with the sample preparation method used here, total leukocyte count proved to be more accurate than total
protein amount as a reference unit for
enzyme activities. Subsequent analysis of 725 individuals showed clear discrimination of
enzyme activities in patient samples (48 MLD; 21
gangliosidoses), with a sensitivity of 100% and specificity of 98-99%.