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What is alpha-mannosidosis?

Alpha-mannosidosis is an ultra-rare, inherited condition known as a lysosomal storage disorder that causes a range of symptoms. It occurs when the body is unable to make an enzyme that breaks down certain glycoproteins, which are a type of sugar, in cells. This causes the sugars to build up in part of the cell called a lysosome, which can damage organs and tissues throughout the body.

a rare disease
affecting about
1 in 500,000-
live births

a hereditary

All forms are progressive,
independent of severity

Symptoms may first
become evident in infancy
or later in adolescence

What causes alpha-mannosidosis?

Alpha-mannosidosis is caused by hereditary mutations in a gene called MAN2B1.

What is a hereditary mutation?

Hereditary mutations are inherited from one’s father or mother, or in the case of alpha-mannosidosis, from both parents.

What is MAN2B1?

The gene MAN2B1 contains the information to make the enzyme α-mannosidase, which normally helps to break down complex sugars called oligosaccharides. Oligosaccharides are used to build bones, cartilage, skin, tendons, and many other tissues in the body.

What happens when α-mannosidase is not working properly?

A defect in the activity of α-mannosidase means that an individual is not able to correctly recycle old oligosaccharides. Due to this, partially broken-down mannose-containing chemicals remain stored in the body and begin to build up over time. This causes progressive damage to cells. Infants may show only a few signs of the disease, but as the disease progresses, symptoms start to appear.

What are the symptoms of alpha-mannosidosis?

Symptoms of alpha-mannosidosis include:

  • Hydrocephalus (fluid build-up in the brain)
  • Recurrent infections
  • Immune deficiency
  • Hearing loss
  • Skeletal abnormalities (such as scoliosis, which is a curvature of the spine)
  • Cognitive impairment
  • Coarse facial features
  • Disturbed motor function (such as muscle weakness and joint abnormalities, which may appear as clumsiness)

Symptoms can vary greatly from person to person and may change as patients get older.

Alpha-mannosidosis is a progressive disease, meaning symptoms will get worse over time as disease progresses.


  • Hearing loss
  • Delayed speech, motor, or mental functions
  • Fluid build-up in the brain in the first year of life

2nd to 3rd decade of life

  • Muscular weakness
  • Ataxia (problems with coordination or balance)
  • Skeletal abnormalities
  • Joint problems
  • Psychiatric symptoms


  • Inability to achieve social independence
  • Life expectancy unknown, although living to over 50 years old is not uncommon