Alpha Mannosidase (Lysosomal storage disorder)

Alpha Mannosidase (Lysosomal Storage Disorder) is a specialized enzyme-activity test used to support the diagnosis of alpha-mannosidosis, a rare inherited lysosomal storage disorder. The test evaluates the activity of lysosomal acid alpha-mannosidase, usually in leukocytes obtained from a blood sample.

Alpha-mannosidase normally helps break down mannose-containing oligosaccharides inside lysosomes, the recycling compartments of cells. Reduced or absent enzyme activity causes these substances to accumulate, which can progressively affect the nervous system, skeleton, hearing, immune system, liver, spleen, and other tissues.

Benefits of the Test

• Measures lysosomal alpha-mannosidase enzyme activity.
• Supports diagnosis of suspected alpha-mannosidosis.
• Helps investigate a positive oligosaccharidosis screening result.
• Assists evaluation of unexplained developmental and neurological symptoms.
• Supports investigation of hearing loss with skeletal or immune abnormalities.
• Helps determine whether confirmatory MAN2B1 genetic testing is required.
• Provides laboratory evidence for specialist metabolic evaluation.
• Supports genetic counselling and family assessment after confirmation.

Why Doctors Recommend This Test

Doctors may recommend this test when a child or adult has developmental delay, intellectual disability, delayed speech, hearing loss, recurrent infections, skeletal abnormalities, muscle weakness, poor coordination, distinctive facial features, enlargement of the liver or spleen, or other features suggestive of a lysosomal storage disorder. It may also be requested after an abnormal urine oligosaccharide screening result.

Preparation Before Test

• No fasting is generally required.
• The test usually requires a fresh anticoagulated whole-blood sample for separation and analysis of leukocytes.
• Confirm the required collection tube, sample volume, transport temperature, and dispatch schedule with the laboratory before collection.
• Samples should be collected and transported according to strict enzyme-assay stability requirements.
• Inform the doctor about recent blood transfusions, stem-cell transplantation, or bone-marrow transplantation.
• Provide details of symptoms, developmental history, hearing problems, recurrent infections, and family history.
• Share previous urine oligosaccharide, enzyme, metabolic, and genetic reports if available.

Normal Reporting Time

The Alpha Mannosidase enzyme test is a specialized lysosomal enzyme assay. Reporting time depends on sample viability, leukocyte separation, assay schedules, internal controls, repeat testing requirements, and quality review. Results may require several working days or longer. Please confirm the expected turnaround time and collection schedule with Focus Diagnostics before providing the sample.

Who Should Take This Test?

This test may be recommended for:

• Children with unexplained developmental or speech delay.
• Individuals with intellectual disability and progressive neurological symptoms.
• Patients with hearing loss and skeletal abnormalities.
• People with recurrent infections and suspected immune dysfunction.
• Patients with ataxia, muscle weakness, or delayed motor development.
• Individuals with hepatosplenomegaly and suspected metabolic disease.
• Patients with a positive urine oligosaccharide screen.
• Individuals advised to undergo testing by a geneticist, neurologist, paediatrician, or metabolic specialist.

Detailed Information

Alpha-mannosidosis is caused by disease-causing variants in the MAN2B1 gene. This gene provides instructions for producing lysosomal acid alpha-mannosidase. When the enzyme is deficient, mannose-rich oligosaccharides cannot be broken down effectively and gradually accumulate within cells.

The disorder follows an autosomal-recessive inheritance pattern. This means an affected individual generally inherits one altered copy of the MAN2B1 gene from each parent. Parents who carry a single altered copy usually do not show symptoms.

Clinical severity varies widely. Symptoms may begin during infancy or childhood, while milder cases can be recognised later. Possible findings include delayed development, learning difficulties, speech impairment, hearing loss, frequent respiratory or ear infections, skeletal abnormalities, reduced bone density, muscle weakness, ataxia, distinctive facial features, and enlargement of the liver or spleen.

Psychiatric or behavioural symptoms can occur in some older affected individuals. The type, onset, and progression of symptoms vary, so the diagnosis cannot be made from physical features alone.

The enzyme assay measures alpha-mannosidase activity in leukocytes. Markedly reduced activity supports alpha-mannosidosis, but the result should be reviewed with clinical findings, screening studies, and molecular testing.

MAN2B1 genetic testing may be recommended to confirm the diagnosis, identify the disease-causing variants, and support family counselling. Genetic confirmation can also help with testing of relatives and future reproductive planning.

This enzyme-activity test is not considered reliable for identifying carriers because carriers may have overlapping enzyme activity. Carrier assessment generally requires targeted genetic testing after the familial variants have been identified.

Recent transfusion or transplantation may affect testing because circulating donor-derived blood cells can alter the measured enzyme activity. Complete clinical and treatment history should therefore be provided to the laboratory.

Additional investigations may include urine oligosaccharide analysis, hearing assessment, skeletal imaging, neurological evaluation, immune-system assessment, and genetic testing. A biochemical geneticist or metabolic specialist should interpret the findings.

A normal enzyme result makes classic alpha-mannosidosis less likely but does not exclude other lysosomal storage disorders with similar symptoms. Further metabolic or genetic testing may be required when clinical suspicion remains high.

At Focus Diagnostics, Alpha Mannosidase testing is coordinated using validated lysosomal enzyme-assay protocols, specialized sample-handling requirements, and established quality-control procedures to support reliable diagnostic evaluation.