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Beta-mannosidosis is a rare inherited disorder affecting the way certain sugar molecules are processed in the body.

Signs and symptoms of beta-mannosidosis vary widely in severity, and the age of onset ranges from infancy to adulthood. Almost all individuals with beta-mannosidosis experience intellectual disability, and some have delayed motor development and seizures. Affected individuals may be prone to depression or have behavioral problems such as hyperactivity, impulsivity or aggression. People with beta-mannosidosis are often extremely introverted.

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. It is difficult to determine the specific incidence of beta-mannosidosis, because people with mild or non-specific symptoms may never be diagnosed.


Variants (also known as 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 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.

Variants 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.


This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

Other Names for This Condition

  • Beta-D-mannosidosis
  • Beta-mannosidase deficiency
  • Lysosomal beta A mannosidosis
  • Lysosomal beta-mannosidase deficiency

Additional Information & Resources

Genetic Testing Information

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Clinical Trials

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed


  • Alkhayat AH, Kraemer SA, Leipprandt JR, Macek M, Kleijer WJ, Friderici KH. Human beta-mannosidase cDNA characterization and first identification of a mutation associated with human beta-mannosidosis. Hum Mol Genet. 1998 Jan;7(1):75-83. doi: 10.1093/hmg/7.1.75. Citation on PubMed
  • Bedilu R, Nummy KA, Cooper A, Wevers R, Smeitink J, Kleijer WJ, Friderici KH. Variable clinical presentation of lysosomal beta-mannosidosis in patients with null mutations. Mol Genet Metab. 2002 Dec;77(4):282-90. doi: 10.1016/s1096-7192(02)00172-5. Citation on PubMed
  • Gort L, Duque J, Fabeiro JM, Zulaica A, Coll MJ, Chabas A. Molecular analysis in two beta-mannosidosis patients: description of a new adult case. Mol Genet Metab. 2006 Dec;89(4):398-400. doi: 10.1016/j.ymgme.2006.07.001. Epub 2006 Aug 14. Citation on PubMed
  • Molho-Pessach V, Bargal R, Abramowitz Y, Doviner V, Ingber A, Raas-Rothschild A, Ne'eman Z, Zeigler M, Zlotogorski A. Angiokeratoma corporis diffusum in human beta-mannosidosis: Report of a new case and a novel mutation. J Am Acad Dermatol. 2007 Sep;57(3):407-12. doi: 10.1016/j.jaad.2007.01.037. Epub 2007 Apr 8. Citation on PubMed
  • Uchino Y, Fukushige T, Yotsumoto S, Hashiguchi T, Taguchi H, Suzuki N, Konohana I, Kanzaki T. Morphological and biochemical studies of human beta-mannosidosis: identification of a novel beta-mannosidase gene mutation. Br J Dermatol. 2003 Jul;149(1):23-9. doi: 10.1046/j.1365-2133.2003.05365.x. Citation on PubMed
  • Zhu M, Lovell KL, Patterson JS, Saunders TL, Hughes ED, Friderici KH. Beta-mannosidosis mice: a model for the human lysosomal storage disease. Hum Mol Genet. 2006 Feb 1;15(3):493-500. doi: 10.1093/hmg/ddi465. Epub 2005 Dec 23. Citation on PubMed

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