Lysosomal Alpha-D-Mannosidase Deficiency; Alpha-Mannosidase B Deficiency


Autosomal recessive

Inheritance from both parents will result in the disease

Age range at onset:

Neonatal, or within first year

Specialists you may see:


Alpha-Mannosidosis is a lysosomal storage disorder, causing abnormalities of the face and skeleton, intellectual disability, hearing problems and immune deficiency leading to recurrent infection. While some infants are born with equinus, most appear normal at birth. Hydrocephaly may develop in the first year.

Facial abnormalities are typically a large head, wide forehead, flattened nasal bridge and prognathism as well as a slight strabismus. Those with Alpha-Mannosidosis may experience myopathy, ataxia, hepatosplenomegaly and episodes of psychosis and hallucination.

Those with early-onset Alpha-Mannosidosis often do not live past childhood, while those with later-onset, milder forms find their symptoms progress much more slowly, and can survive into their fifties.


Alpha-Mannosidosis is a deficiency of lysosomal alpha-mannosidase, caused by mutations in the MAN2B1 gene. The MAN2B1 gene creates an enzyme which works in lysosomes to break down sugar molecules such as mannose. Inability to break down these molecules causes them to build up and causes cells to malfunction and die. This damages tissue and organs, causing the symptoms described.

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