Novel storage products in humanβ‐mannosidosis

Abstract

Lysosomal fl-mannosidase (EC 3.2.1.25) is the final enzyme involved in the catabolism of the oligosaccharide side-chains of glycoproteins. Following the description of caprine fl-mannosidosis in the early 1980s, several human patients with a deficiency of this enzyme were described (Cooper et al., 1986;Wenger et al., 1986;Dorland et at., 1988). Defects in lysosomal enzymes usually lead to storage and urinary excretion of incompletely catabolized oligosaccharides. Identification of these urinary excretion products may be helpful in establishing the diagnosis. In human fl-mannosidosis only an abnormal amount of the disaccharide mannosyl-fi(1--.4)-N-acetylglucosamine (Manfi(1-~4)GlcNAc) has been reported so far, in contrast with the much larger and more complex oligosaccharides observed in a-mannosidosis.Generally the structures of the excreted metabolites are those predicted based on the inherited deficiencies of specific exoglycosidases and the coincident action of an endo-fl-N-acetylglucosaminidase which cleaves the linkage between the two GlcNAc residues of the di-N-acetylchitobiose core. Here we describe the occurrence of a sialyloligosaccharide which is probably formed by enzymatic synthesis from the storage product Manfl(1 ~4)GlcNAc as substrate. Furthermore, the characterization is described of a urinary carbohydrate-urea conjugate. PATIENTSThe clinical histories of A.B. and H.B., two brothers born to a consanguineous Turkish couple, have been described before (Dorland et al., 1988). Recently another male child was born in this family. Analysis of oligosaccharides in urine as well as measurement of fl-mannosidase in plasma yielded entirely normal results. METHODSOligosaccharides were isolated from the patients' urine by the following sequence of techniques: concentration by rotary evaporation or lyophilization, cation-and anionexchange purification, gel filtration chromatography on Bio-Gel P2, and preparative 273

Development of a new tandem mass spectrometry method for urine and amniotic fluid screening of oligosaccharidoses

“…In the same urine, other possible specific precursor ions (m/z 418, 480, and 545 in negative mode, 307 in positive mode) were found, for which the structure is not known. Other compounds of higher MW identified by others (NeuAc-Man-GlcNAc [36][37][38][39] ) were not detected. In one NAGA deficiency urine sample, MRMs possibly corresponding to GalNAc-O-Ser in negative mode and to GalNAc-O-Thr in positive mode were found (Supplementary Table S1, Supporting Information).…”

“…For β-mannosidosis and NAGA deficiency urine samples, possible specific MRMs were searched either from the literature, [4,5,25,[35][36][37][38][39] or from high responsive precursor ions that were visible on the precursor ion scan.…”

The structure of mammalian β‐mannosidase provides insight into β‐mannosidosis and nystagmus

“…Humans possess a lysosomal glycosidase, chitobiase, which is able to compensate partially for the lack of β‐mannosidase activity as it participates in degradation of N‐linked oligosaccharides by cleaving between GlcNAc(β1–4)GlcNAc . Therefore, a lack of β‐mannosidase in humans results in cellular storage and secretion in the urine of the disaccharide, Man(β1–4)GlcNAc, whereas in ruminants, which are devoid of chitobiase, storage of the trisaccharide Man(β1–4)GlcNAc(β1–4)GlcNAc predominates . Ultimately, this leads to human cases of β‐mannosidosis having milder symptoms and a more heterogeneous clinical expression compared to the ruminant equivalent, as well as to other human LSDs in which the storage products are larger .…”