Alpha-Mannosidosis

Alpha mannosidosis  is a lysosomal storage disorder, a form of inborn metabolic disease. It is characterized by intellectual disability, hearing loss, ataxia, skeletal abnormalities, and coarse facial features.Signs and symptoms vary, but often include mild to moderate intellectual disability, hearing loss, weakened immune system, distinctive facial features, and cerebellar disorders (e.g., ataxia). Symptoms slowly worsen over time.

According to the severity of the symptoms it is classified in 3 sub-types:

• Type 1: A mild form recognized after age ten years with absence of skeletal abnormalities, muscle problems (myopathy), and slow progression
• Type 2: A moderate form recognized before age ten years with presence of skeletal abnormalities, myopathy, and slow progression. It is the most common form.
• Type 3: A severe form manifested as pregnancy loss or early death from progressive central nervous system involvement.

Alpha mannosidosis is caused by a mutations in the MAN2B1 gene,  which codifies a type of enzyme (lysosomal alpha-mannosidase), that degrade glycoproteins (proteins attached to sugar residues) into smaller fragments. The lack or deficiency of this enzyme results in the toxic build-up of sugars (i.e., mannose-containing oligosaccharides) in the cells of the body. Inheritance is autosomal recessive. Treatment aims to avoid complications and improve the quality of life. Ongoing research for new treatments include bone marrow transplant and enzyme replacement.