Definition:

Alpha-mannosidosis is an autosomal recessive lysosomal storage disorder caused by deficient activity of alpha-mannosidase in glycoprotein catabolism. The enzymatic defect results in the accumulation of mannose-rich oligosaccharides in many organs. Alpha-mannosidosis is characterized by immune deficiency, facial and skeletal abnormalities, hearing impairment, and mental retardation. The disorder has been described as two distinct phenotypes: a severe form with hepatomegaly and early death following severe infections (type 1) and a mild form with hearing loss and mental retardation (type 2).