Diagnostic screening for mucopolysaccharidoses types I-VII by fluorophore-labelled carbohydrate PAGE.

Proteoglycans, constituents of the extracellular matrix of various tissues, are proteins that contain covalently linked glycosaminoglycans (GAG). They are processed by proteases and endoglycosidases into highly sulphated, high-molecular-weight polysaccharides. In the lysosomes these GAG are degraded further, in a sequential manner, to lower-molecular-weight fragments and monomers by specific sulphatases and exoglycosidases acting on the non-reducing end of the GAG molecules. In the mucopolysaccharidoses (MPS), lysosomal degradation proceeds normally until a linkage is reached at the non-reducing terminus for which a specific enzyme is lacking. Sequential degradation stops at this point, resulting in the accumulation of chondroitin (CS a and c), dermatan (DS), heparan (HS) and keratan (KS) ; however, degradation by endoglycosidases continues. These enzymes produce the lower-molecular-weight fragments found in the urine and tissues of MPS patients. One can speculate that each of the enzyme deficiencies should present a different array of residual GAG fragments. The definitive diagnosis of the MPS rests upon the determination of specific enzyme activities ; however, these studies are restricted to a few specialized laboratories and are not amenable to general screening. For such purposes, methods should be rapid, reliably identify most of the MPS defects, and exclude normal patients from the numerous cases suspected on the basis of their clinical presentation. All the existing non-enzymatic screening methods for MPS are based on the detection of CS a and c, DS, HS and KS by thin-layer chromatography (TLC) and combined cellulose acetate gel electrophoresis (Dembure and Roesel 1991). It is the purpose of this communication to report a new screening protocol based on the detection of GAG fragments using fluorophore-assisted carbohydrate electrophoresis (GLYKO-FACE kit).