Alpha-mannosidosis is an inherited disease characterized by developmental delays, facial and skeletal abnormalities, hearing loss, and immune deficiency. It is caused by abnormalities in the enzyme alpha-mannosidase that breaks down small sugar molecules called oligosaccharides. Symptoms associated with alpha-mannosidosis are due to the toxic build-up of oligosaccharides and the progressive destruction of cells, particularly in the central nervous system. View testing options