Fucosidosis: Detection of the carrier state in peripheral blood leukocytes

We have utilized the fluorogenic substrate 4-methylumbelliferyl-α-l-fucoside to measure the activity of α-l-fucosidase in white blood cells and serum. We have compared the findings with those using the p-nitrophenyl derivative. pH activity curves showed two major peaks of activity in leukocyte lysates, with different specificities to these substrates. α-l-Fucosidase activity was determined in peripheral leukocytes. isolated mononuclear cells (mainly lymphocytes), and granulocytes in 21 members of a family in which fucosidosis had occurred and in normal control subjects. The activity in the leukocytes, lymphocytes, and granulocytes of the normal subjects was 300.7±79.8, 190.1±43.9, and 281.9±73.1 nmoles 4-methylumbelliferone/mg protein/hour with the fluorogenic substrate, and 150.0±31.8, 154.8±21.0, and 148.3±48.3 nmoles p-nitrophenol/mg protein/hour with the colorigenic substrate, respectively. No activity was detected in the patients' cells with the colorigenic substrate, whereas with the fluorogenic substrate the apparent activity varied from 0.5 to 1.1. In the lymphocytes of both of the patients' parents, two grandparents, and six other potential carriers, the activity fell between the normal and patients' values. Great variation in α-l-fucosidase activity, with broad overlap between normal subjects and heterozygotes, was observed in serum and plasma. Our findings indicate that detection of carriers for fucosidosis is possible by direct fucosidase determinations in isolated mononuclear cells.