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

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Abstract
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 α‐mannosidase activity. Kinetic analyses showed that α‐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 α‐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.