Low beta-glucuronidase activity in a healthy member of a family with mucopolysaccharidosis VII.

A phenotypically normal mother of a mucopolysaccharidosis VII child, is reported with an unusually low beta-glucuronidase activity. Low enzyme activity was systemic (6-10% of controls) and residual beta-glucuronidase in leukocytes had an apparently normal Km value. [35S]sulphate incorporation and chase assays in fibroblasts gave values similar to control cells. A normal excretion pattern of glycosaminoglycan was found in this woman's urine. Low enzymatic activity can be related to a non-pathological 'pseudodeficiency' allele for beta-glucuronidase; this woman appears to be an apparent compound heterozygote for this allele and mucopolysaccharidosis VII. Her next pregnancy was monitored by chorionic villus sampling and a heterozygous fetus was suspected. These studies stress the need for complete enzyme investigations of obligate carriers for mucopolysaccharidoses in order to prevent difficulties at prenatal analysis.