Complementation studies in human and caprine β-mannosidosis

Cell fusions were performed to investigate the possible involvement of different gene mutations in five patients with isolatedβ-mannosidosis and a patient with a combined deficiency ofβ-mannosidase and heparan sulphate sulphamidase. In none of the combinations of cell lines wasβ-mannosidase activity restored in the fused cell culture. Similarly, no complementation of sulphamidase activity was observed after fusion of cells with the combined deficiency and cells with isolated sulphamidase deficiency (mucopolysaccharidosis type IIIA). The absence of complementation suggests that the combined deficiency is not caused by a defect in one common factor affecting the two enzymes: The results rather indicate a rare coincidence of two independent mutations which are allelic with the mutation in the respective conditions with isolated enzyme deficiencies.