ALPHA MANNOSIDOSIS--Type II and III

ALTERNATE NAMES

Alpha Mannosidosis Types II/III Early Onset Forms; Alpha-D- mannosidosis; Alpha-mannosidase B deficiency; Alpha-mannosidase deficiency; Lysosomal alpha B mannosidosis; Lysosomal alpha-D-mannosidase deficiency; Mannosidosis lipid storage disease; Inborn error of metabolism; MAN2B1 gene abnormality; Mannosidosis

DESCRIPTION

Alpha Mannosidosis is a rare inherited metabolic storage disease caused by a mutation in the gene for alpha-mannosidase, an enzyme that normally breaks down sugars (carbohydrates) in lysosomes. Because of the mutation, sugars abnormally accumulate and impair the function of cells in the brain and other organs. Signs and symptoms of alpha-mannosidosis include intellectual disability, hearing loss, distinctive facial features, enlarged liver and spleen, immune dysfunction leading to frequent infections, and skeletal abnormalities, such as reduced bone density, deformations of the bones in the spine, bowed or knocked knees, and deterioration of bones and joints.

DIAGNOSTIC TESTING, PHYSICAL FINDINGS, AND ICD-9-CM CODING

Diagnostic testing: A confirmed diagnosis is documented by abnormally low or absent levels of alpha-D-mannosidase enzymatic activity in white blood cells.

Physical findings: Cognitive and motor developmental delay, or intellectual disability; hepatosplenomegaly (enlargement of the liver and spleen), large head, protruding forehead, low hairline, rounded eyebrows, large ears, flattened bridge of the nose, protruding jaw, widely spaced teeth, overgrown gums, large tongue, cataracts, vertebral anomalies, long bone and joint abnormalities, ataxia, and myopathy.

ICD-9: 278.8

ONSET AND PROGRESSION

Type III alpha mannosidosis is the most severe form, and signs and symptoms appear in infancy with rapid progression, severe neurological deterioration, and early death. In Type II, symptoms appear before age 10, and progressive deterioration is not as rapid as in Type III. For children with Type I, symptoms appear after age 10 and progress slowly; affected children have muscle weakness but not skeletal abnormalities, and they may live well into adulthood.

TREATMENT

There is no cure or treatment to alter the progression of alpha-mannosidosis. There are, however, symptomatic treatments that are used. For example, anticonvulsants can help to control seizures. Hearing aids improve ability to hear and communicate. Physical therapy may improve motor function, and assistive devices can aid with mobility. New and promising therapies for alpha mannosidosis include bone marrow transplantation, enzyme replacement, and gene therapy.

SUGGESTED PROGRAMMATIC ASSESSMENT*

Suggested MER for evaluation:

• Clinical history and examination that describes the diagnostic features of the impairment

• Laboratory studies of alpha D-mannosidase enzymatic activity in white blood cells

Suggested Listings for Evaluation:

DETERMINATION

LISTING

Meets Listing

110.08

112.02

Medical Equals