Alpha mannosidosis is an autosomal recessive disorder presenting with three clinical subtypes; mild, moderate and severe form. Patients with a milder phenotype have mild-to-moderate mental retardation, characteristic coarse features, skeletal abnormalities, reduced hearing, immunodeficiency, and primary central nervous system disease, mainly cerebellar involvement causing ataxia. Other medical problems include corneal opacities, hepatosplenomegaly, aseptic destructive arthritis, and metabolic myopathy. Alpha-mannosidosis is insidiously progressive; individuals may live into the sixth decade.

Affected individuals may have an abnormal urine oligosaccharide pattern. Confirmation is made by measurement of alpha-mannosidosis directly.