A granulocyte test for detection of cattle heterozygous for mannosidosis

A comparison of fluorimetric and colorimetric methods for the determination of alpha-mannosidase activity in bovine plasma

This paper compares both manual colorimetric and fluorimetric methods for the assay of acidic alpha-mannosidase activity in bovine EDTA plasma. The effect of variable blood volumes per 10 ml blood collecting tube has been investigated, and the colorimetric assay conditions adjusted (for example, zinc concentration in pre-incubation buffer) to cope with low blood volumes resulting in high EDTA/plasma ratios. We have shown that with non-haemolysed EDTA plasma samples, the two methods give similar results, but for haemolysed samples, the colorimetric method yields significantly lower results than those obtained fluorimetrically. Using the manual fluorimetric method, samples can be assayed more rapidly and simply than by using the colorimetric method. This provides definite advantages in a laboratory receiving variable numbers of samples, or which cannot afford the high cost of automated equipment.

Use of EDTA blood samples for mannosidosis testing

Preincubation of EDTA plasma with 4mM ZnCl2 restores acidic alpha mannosidase activity, previously inhibited as a result of chelation of Zn++ by EDTA. This allows estimation of acidic alpha mannosidase activity in EDTA plasma samples, followed by granulocyte tests on those samples with low activities.

An improved fluorimetric determination of alpha-mannosidase activity in bovine plasma

This paper describes a manual fluorimetric method for the assay of acidic alpha-mannosidase activity in bovine plasma. The optimum conditions for the assay of this enzyme were studied. The assay method devised includes the addition of zinc to the substrate, which stimulates activity by approximately twofold, and reduces the optimum substrate concentration. This latter feature affords considerable cost saving in each test. We have also shown that the alpha-mannosidase activity in lithium heparin plasma, EDTA plasma and blood serum is the same whether the plasma/serum is separated from the cells/clot at 6, 20 or 25 hours after sample collection. This has eliminated the previous necessity of having to deliver whole blood samples to the laboratory within 6 hours of collection. Furthermore samples for the supplementary neutrophil assay can now be taken at the same time as those for the plasma test, and both samples forwarded together. The plasma alpha-mannosidase assay is a rapid and reliable screening test for the mannosidosis genotype and for detecting carrier animals. Carrying out this plasma assay in conjunction with the more definitive neutrophil assay provides a reliable method of distinguishing homozygotes and heterozygotes from normal animals.

Inborn errors of lysosomal catabolism--principles of heterozygote detection

Carriers of an inborn error of lysosomal catabolism can be recognized, as they have enzyme levels approximately half those of normal individuals. Of the various tissues readily available for assay, plasma and leukocytes and, in some situations, tears are preferred. Although mixed leukocytes have proved satisfactory in Tay-Sachs screening programs, purified preparations of granulocytes or lymphocytes will allow better discrimination in most situations. Enzymes are assayed relative to some other reference parameter which must be a constant or highly correlated with test enzyme activity. In the two mass screening programs in operation, beta-hexosaminidase A and alpha-mannosidase have both been assayed relative to total beta-hexosaminidase activity. Carrier detection is particularly important in X-linked diseases. The techniques used mostly involve hair roots or fibroblasts and depend on random inactivation of the X chromosome. In the mucolipidoses II and III, in which there are a number of deficient enzymes in cells, carriers may be identified on the basis of the ratio of beta-hexosaminidase I1 and I2 to total hexosaminidase.