Gene : MAN2B1

What is alpha-mannosidosis?

Alpha-mannosidosis is a rare disorder characterized by lack of muscle coordination, coarse facial features, skeletal abnormalities, hearing loss, and intellectual disability. This is due to the defective enzyme alpha-mannosidase. There are three forms of this disorder, separated by age of onset and severity of symptoms. The mild form typically begins to shows signs of the disease after age 10. Individuals with this form develop muscle weakness that slowly deteriorates as they get older. They typically do not have skeletal abnormalities and may survive into their fifties. People with the moderate form are usually identified before age 10 with skeletal abnormalities and more severe muscle weakness that will progress to a severe muscle problem between 20 and 30 years old. Survival is well into adulthood. In the most severe form, death occurs before birth or early in childhood due to rapid disintegration of their nervous system. These children will also have skeletal abnormalities. People with alpha-mannosidosis can also have frequent infections because their immune system doesn't work properly. There is no cure for alpha-mannosidosis; however medical surveillance and care may help to improve some symptoms and overall condition of life. Alpha-mannosidosis is caused by pathogenic variants in the MAN2B1 gene.

How is alpha-mannosidosis inherited?

Alpha-mannosidosis is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for alpha-mannosidosis. However, the risk to have a child affected with alpha-mannosidosis is increased. Testing of reproductive partners is recommended for carriers of alpha-mannosidosis.

How common is alpha-mannosidosis?

Alpha-mannosidosis is very rare. It is estimated to affect 1 in every 500,000 newborns.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems







Carrier Rates
Detection Rate
Carrier Frequency
General Population 98% 1 in 354
Northern European Caucasian 98% 1 in 354

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