Beta-mannosidosis is a very rare lysosomal storage disease characterized by developmental delay of varying severity and hearing loss, but that can manifest a wide phenotypic heterogeneity. The disease is beta-mannosidosis (MONDO_0009562). Also known as: Beta-D-mannosidosis, Beta-mannosidase deficiency, beta-mannosidase deficiency, lysosomal beta-mannosidase deficiency, mannosidosis, beta.