Mannosidosis, Alpha B

Background and History: 

Mannosidosis, of which there are at least two types, is a rare but severe and progressive generalized disorder of metabolism known as a lysosomal storage disease.

Clinical Correlations: 

There is considerable variability in the onset and progression of symptoms in mannosidosis.  The most severe disease is found in infants who have severe motor and mental deficits and often die young.  In many other patients, though, symptoms may not appear until adulthood and these individuals may live until the sixth decade or later.  Coarse facies, a large head, large tongue and large ears are often present in adults.  Cognitive deficits of a progressive nature are common as the disease is relentlessly progressive.  Difficulties with balance (ataxia) and weakness of muscles are common.  The liver and kidneys are often enlarged.  Frequent infections are common, particularly in childhood.  Most patients have some hearing loss and the teeth often have wide spaces between them.  Speech is often slurred and joints are often stiff.  Thinning and deformities of bones may occur.  Psychiatric symptoms of depression and anxiety often occur.

It is unknown how many patients have ocular disease.  Cataracts, deterioration of the retina and optic nerve, and some clouding of the cornea have been reported.  It is often difficult to test vision but where possible evidence suggests that vision can be normal early in life but becomes worse later.


This is an autosomal recessive condition in which the parents, each of whom carries the mutation, are clinically normal but affected individuals have both mutated copies of the abnormal gene.  Of course, such couples can expect a 25% risk of mannosidosis in each of their children.

Diagnosis and Prognosis: 

The diagnosis of mannosidosis is usually the result of a team effort by pediatricians and neurologists.  Orthopedists and dentists may also contribute.  Most patients do not live a healthy life.  Infants with the severe form of the disorder may die in the first year of life.  Older individuals may live for many decades but experience a downhill course in mental and motor functions.

There is no specific treatment for this disorder.  Assistive devices such as hearing aids, orthopedic devices, and wheelchairs can be helpful.  Evidence of infection should lead to prompt treatment when indicated.  Annual checkups are important.

Additional Information
Autosomal recessive