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The genes in this family provide instructions for making proteins that are involved in the production (biosynthesis) of molecules called phosphatidylinositol glycan anchors (commonly called GPI anchors). GPI anchors attach (bind) to various proteins and anchor them to the outer surface of cell membranes. This anchoring is necessary for the functioning of most cells and to ensure the availability of the proteins at the cell surface, but the specific purpose of the anchoring is largely unknown.
The biosynthesis of GPI anchors occurs in a series of steps that take place in the endoplasmic reticulum, which is a structure involved in protein processing and transport within cells. The first step occurs when a group of phosphatidylinositol glycan (PIG) proteins come together to form an enzyme complex and create the basic structure of a GPI anchor. In subsequent steps, PIG proteins add various molecules, including sugars and fats, to the growing GPI anchor. Lastly, PIG proteins form an enzyme complex called GPI transamidase that brings together complete GPI anchors with the proteins that bind to them. The GPI-anchor associated protein is transferred to a cell structure called the Golgi apparatus, which modifies newly produced enzymes and other proteins, for further refining. From the Golgi apparatus, the protein is transported, then anchored, to the surface of the cell membrane.
Mutations in several PIG genes in the phosphatidylinositol glycan anchor biosynthesis pathway can cause genetic disorders. An error in anchor biosynthesis results in an incomplete GPI anchor that cannot attach to proteins. A lack of GPI anchoring prevents certain proteins from being attached to the cell membrane and results in their abnormal release from the cell, leading to unusually high amounts of that protein in the blood. For example, mutations in the PIGO or PIGV gene cause Mabry syndrome, a condition characterized by intellectual disability, distinctive facial features, and increased levels of an enzyme called alkaline phosphatase in the blood (hyperphosphatasia).
The HUGO Gene Nomenclature Committee (HGNC) provides a list of genes in the PIG family (http://www.genenames.org/genefamilies/PIG).
Genetics Home Reference summarizes the normal function and health implications of these members of the PIG gene family: PIGA, PIGO, and PIGV.
Genetics Home Reference includes these conditions related to genes in the PIG gene family:
You may find the following resources about the PIG gene family helpful.
cell ; cell membrane ; class ; disability ; endoplasmic reticulum ; enzyme ; gene ; glycan ; Golgi apparatus ; phosphatase ; protein ; syndrome
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).
These sources were used to develop the Genetics Home Reference summary for the PIG gene family.
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.