beta-Mannosidase deficiency was demonstrated in fibroblasts of a girl who showed severe psychomotor retardation, bone deformities and gargoylism and recurrent skin and respiratory infections and who died at 20 years of age from bronchopneumonia. This first demonstration of a female patient confirms the autosomal recessive inheritance of beta-mannosidosis. Further investigation of this gypsy family revealed beta-mannosidosis in an older brother with a milder manifestation of gargoyl facial dysmorphology, mental retardation, hearing impairment and recurrent infections. beta-Mannosidase activity was completely deficient in his cultured skin fibroblasts, leukocytes and plasma. In urine a characteristic disaccharide was present. Heterozygote levels of beta-mannosidase were found in fibroblasts and/or plasma of the parents and one sister.

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Cell fusions were performed to investigate the possible involvement of different gene mutations in five patients with isolated beta-mannosidosis and a patient with a combined deficiency of beta-mannosidase and heparin sulphate sulphamidase. In none of the combinations of cell lines was beta-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.