Skip navigation

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

URL of this page:

PMM2 gene

phosphomannomutase 2

Normal Function

The PMM2 gene provides instructions for making an enzyme called phosphomannomutase 2 (PMM2). This enzyme is involved in a process called glycosylation, which attaches groups of sugar molecules (oligosaccharides) to proteins. Oligosaccharides are made up of many small sugar molecules that are attached to one another in a long chain. Glycosylation modifies proteins so they can perform a wider variety of functions. In one of the early steps of glycosylation, the PMM2 enzyme converts a molecule called mannose-6-phosphate to mannose-1-phosphate. Subsequently, mannose-1-phosphate is converted into GDP-mannose, which can transfer its small sugar molecule called mannose to the growing oligosaccharide chain. Once the correct number of small sugar molecules are linked together to form the oligosaccharide, it can be attached to a protein.

Health Conditions Related to Genetic Changes

PMM2-congenital disorder of glycosylation

More than 115 mutations in the PMM2 gene have been found to cause PMM2-congenital disorder of glycosylation (PMM2-CDG, also known as congenital disorder of glycosylation type Ia). This is a severe condition that is characterized by developmental delay, weak muscle tone (hypotonia), abnormal distribution of fat, and various other signs and symptoms. The mutations that cause PMM2-CDG change the structure of the PMM2 enzyme in different ways; however, all of the mutations appear to result in reduced enzyme activity. Decreased activity of the PMM2 enzyme leads to a shortage of GDP-mannose within cells. As a result, there is not enough activated mannose to form oligosaccharides. Glycosylation cannot proceed normally because incorrect oligosaccharides are produced. The signs and symptoms in PMM2-CDG are likely due to the production of abnormally glycosylated proteins in many organs and tissues.

More About This Health Condition

Other Names for This Gene

  • CDG1a
  • phosphomannomutase
  • PMM

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • de la Morena-Barrio ME, Hernandez-Caselles T, Corral J, Garcia-Lopez R, Martinez-Martinez I, Perez-Duenas B, Altisent C, Sevivas T, Kristensen SR, Guillen-Navarro E, Minano A, Vicente V, Jaeken J, Lozano ML. GPI-anchor and GPI-anchored protein expression in PMM2-CDG patients. Orphanet J Rare Dis. 2013 Oct 20;8:170. doi: 10.1186/1750-1172-8-170. Citation on PubMed or Free article on PubMed Central
  • Freeze HH. Towards a therapy for phosphomannomutase 2 deficiency, the defect in CDG-Ia patients. Biochim Biophys Acta. 2009 Sep;1792(9):835-40. doi: 10.1016/j.bbadis.2009.01.004. Citation on PubMed or Free article on PubMed Central
  • Gao N, Shang J, Lehrman MA. Analysis of glycosylation in CDG-Ia fibroblasts by fluorophore-assisted carbohydrate electrophoresis: implications for extracellular glucose and intracellular mannose 6-phosphate. J Biol Chem. 2005 May 6;280(18):17901-9. doi: 10.1074/jbc.M500510200. Epub 2005 Feb 11. Citation on PubMed or Free article on PubMed Central
  • Grunewald S. The clinical spectrum of phosphomannomutase 2 deficiency (CDG-Ia). Biochim Biophys Acta. 2009 Sep;1792(9):827-34. doi: 10.1016/j.bbadis.2009.01.003. Epub 2009 Jan 14. Citation on PubMed
  • Haeuptle MA, Hennet T. Congenital disorders of glycosylation: an update on defects affecting the biosynthesis of dolichol-linked oligosaccharides. Hum Mutat. 2009 Dec;30(12):1628-41. doi: 10.1002/humu.21126. Citation on PubMed
  • Lam C, Krasnewich DM. PMM2-CDG. 2005 Aug 15 [updated 2021 May 20]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.