Acid beta-mannosidase of human plasma: influence of age and sex on enzyme activity.

Optimum conditions for assay of human plasma beta-mannosidase activity were determined. Maximum activity was observed at pH 3.0-3.4, the apparent Km was 0.9 mmol L-1 and enzymatic hydrolysis was linear for at least 60 min. Assays were performed on plasma from two siblings with the recently described condition beta-mannosidosis and their parents and controls. Both beta-mannosidosis patients showed a marked deficiency of beta-mannosidase activity. Control samples showed no variation between sexes (p greater than 0.05) but enzyme activity varied significantly with age (p less than 0.05). Highest activity was observed in the 0-1 year age group, activity then decreasing to adulthood, Both mother and father of the affected individuals showed reduced activity (34% and 53%, respectively) compared to age-matched controls. This suggests that heterozygote detection in this condition is possible using plasma, provided the variation of activity with age is taken into consideration.