Isozyme pattern of leukocyte alpha-D-mannosidase in patients with mannosidosis

Lysosomal enzyme activities in skeletal muscle of patients with neuromuscular diseases

Activities of nine lysosomal enzymes and pH-dependent isozyme patterns of alpha-mannosidase were examined in the skeletal muscle of patients with neuromuscular diseases, and the ratios of these enzyme activities in leukocytes to those in myocytes (L/M ratio) were determined. The activities of enzymes with a high L/M ratio were markedly increased in the muscles of patients with Duchenne muscular dystrophy (DMD), myotonic dystrophy (MyD), or polymyositis (PM). In contrast, those which showed a low L/M ratio were increased in the muscles of amyotrophic lateral sclerosis (ALS) and disuse muscle atrophy (DUA). The isozyme pattern of alpha-mannosidase in DMD muscle resembled that in leukocytes, while those in ALS and DUA muscle resembled that in normal muscle. These results may suggest that the increased activity of lysosomal enzymes in the muscles of patients with DMD, MyD, or PM is due primarily to infiltrating leukocytes, while that in patients with ALS or DUA is due to intramyofiber lysosomes.

Clinical and biochemical analysis of two families with type I and type II mannosidosis

We report on two unrelated patients with different presentations of mannosidosis. One patient was affected in early childhood with a severe phenotype characteristic of type I mannosidosis. The other was diagnosed with type II mannosidosis only after the onset of progressive neurologic deterioration in late adulthood. Both were detected by non-invasive urinary screening of oligosaccharides. Lymphoblasts transformed from both patients' blood cells had markedly reduced lysosomal alpha-mannosidase activity. Kinetic analyses showed that alpha-mannosidase from the type I patient had a 400-fold reduction in affinity while that from the type II patient was reduced 40-fold. Lymphoblasts from all 4 parents had reduced alpha-mannosidase activity, but there were overlapping activities among these type I and type II obligate heterozygotes. We conclude that screening urinary oligosaccharides will detect mannosidosis over a wide range of phenotypes, that lymphoblasts transformed from affected heterozygotes have decreased enzymatic activity, and that the severity of clinical expression is related to the degree of enzyme impairment.