What is Beta-mannosidosis Beta-mannosidosis?
Beta-mannosidosis is a rare inherited disorder affecting the way certain sugar molecules are processed in the body. Beta-mannosidosis, also called lysosomal beta-mannosidase deficiency, is a disorder of oligosaccharide metabolism caused by decreased activity of the enzyme beta-mannosidase. This enzyme is coded for by the gene MANBA, located at 4q22-25. Beta-mannosidosis is inherited in an autosomal recessive manner.Affected individuals appear normal at birth, and can have a variable clinical presentation. Infantile onset forms show severe neurodegeneration, while some children have intellectual disability. Hearing loss and angiokeratomas are common features of the disease, however because it is so rare, the full phenotype associated with the disease is not fully understood.
Signs and symptoms?
of beta-mannosidosis vary widely in severity, and the age of onset ranges between infancy and adolescence. Almost all individuals with beta-mannosidosis experience intellectual disability, and some have delayed motor development and seizures. Affected individuals may be extremely introverted, prone to depression, or have behavioral problems such as hyperactivity, impulsivity or aggression. People with beta-mannosidosis may experience an increased risk of respiratory and ear infections, hearing loss, speech impairment, swallowing difficulties, poor muscle tone (hypotonia), and reduced sensation or other nervous system abnormalities in the extremities (peripheral neuropathy). They may also exhibit distinctive facial features and clusters of enlarged blood vessels forming small, dark red spots on the skin (angiokeratomas).
Beta-mannosidosis is believed to be a very rare disorder. Approximately 20 affected individuals have been reported worldwide. It is difficult to determine the specific incidence of beta-mannosidosis, because people with mild or non-specific symptoms may never be diagnosed.
What gene is related to Beta-mannosidosis?Mutations in the MANBA gene cause beta- mannosidosis. The MANBA gene provides instructions for making the enzyme beta-mannosidase. This enzyme works in the lysosomes, which are compartments that digest and recycle materials in the cell. Within lysosomes, the enzyme helps break down complexes of sugar molecules (oligosaccharides) attached to certain proteins (glycoproteins). Beta-mannosidase is involved in the last step of this process, helping to break down complexes of two sugar molecules (disaccharides) containing a sugar molecule called mannose. Mutations in the MANBA gene interfere with the ability of the beta-mannosidase enzyme to perform its role in breaking down mannose-containing disaccharides. These disaccharides gradually accumulate in the lysosomes and cause cells to malfunction, resulting in the signs and symptoms of beta-mannosidosis.
Inheritence pettarn?-This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Other name of this condition?
Diagnosis?-A diagnosis of beta-mannosidosis is suspected based on the patients clinical presentation. Urine testing to identify abnormal oligosaccharides is a useful screening test, and enzymatic analysis or molecular testing can be used for confirmation. Currently, there is no treatment for individuals affected with beta-mannosidosis.
When to contact a Medical Professional?When a diagnosis beta-mannosidosis of is made. When pregnancy is planned in a family with history of beta-mannosidosis disease.
Who to contact for more information?The Department of Health Research and Indian Council of Medical Research have constituted a National Task Force to perform a multicentric collaborative study at different research institutes across the country. Further information can be found at http://www.icmrmetbionetindia.org/task- force-disoredrs.php Lysosomal Storage Society of India - LSDSS http://www.lsdss.org
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Dr Parag Tamhankar
Genetic Research Centre, Mumbai