Isozyme pattern of leukocyte α-d-mannosidase in patients with mannosidosis

The isozyme patterns of leukocyte -d-mannosidase in two sisters with mannosidosis, their parents and a patient with trisomy 19 were studied. The isozyme pattern of liver mannosidase of a normal subject was also studied. In the patients with mannosidosis the neutral isozyme (isozyme C or fraction C) was present, but the acidic isozymes (isozyme A and B or fraction A and B) were not detectable. In their parents the activity of the acidic isozymes was one-third of the normal activity. These findings suggest that the patients are homozygous and their parents are heterozygous in terms of deficiency of acidic isozymes. In the patients with trisomy 19, the activity of -d-mannosidase was 4.9 times the upper limit of the normal value, while the levels of other lysozomal enzymes were normal. This increase was mainly due to increases of the A and B isozymes of mannosidase. This finding suggests that the gene encoding acidic isozymes, but not that encoding the neutral isozyme, is located on chromosome 19. The isozyme pattern of -d-mannosidase differed in different tissues of normal subjects, and the difference in severity of lesions in different organs of the patients with mannosidosis could be explained by differences in the isozyme patterns of the enzyme in these organs.