Human beta-mannosidase deficiency: biochemical findings in plasma, fibroblasts, white cells and urine

Marked deficiencies of beta-mannosidase activity were demonstrated in plasma, leukocytes, fibroblasts and urine of a patient with beta-mannosidosis, similar deficiencies were observed in the proband's sibling. All other lysosomal enzymes measured, including sulphamidase, exhibited normal activity. Both parents showed reduced plasma and leukocyte beta-mannosidase activity. Urinary glycosaminoglycan excretion was normal but TLC of urinary oligosaccharides revealed an abnormal band with the mobility of a disaccharide. This finding was confirmed by Bio-Gel P2 column chromatography. Further purification of this compound revealed two disaccharides, both of which yielded mannose and glucosamine following acid hydrolysis and mannose and N-acetylglucosamine following enzymic digestion. These two compounds are thought to be structural isomers of the disaccharide Man beta-GlcNAc.