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The official name of this gene is “GNAS complex locus.”
GNAS is the gene's official symbol. The GNAS gene is also known by other names, listed below.
The GNAS gene provides instructions for making one component, the stimulatory alpha subunit, of a protein complex called a guanine nucleotide-binding protein (G protein). Each G protein is composed of three proteins called the alpha, beta, and gamma subunits.
In a process called signal transduction, G proteins trigger a complex network of signaling pathways that ultimately influence many cell functions by regulating the activity of hormones. The protein produced from the GNAS gene helps stimulate the activity of an enzyme called adenylate cyclase. This enzyme is involved in controlling the production of several hormones that help regulate the activity of endocrine glands such as the thyroid, pituitary gland, ovaries and testes (gonads), and adrenal glands. Adenylate cyclase is also believed to play a key role in signaling pathways that help regulate the development of bone (osteogenesis). In this way, the enzyme helps prevent the body from producing bone tissue in the wrong place (ectopic bone).
GNAS gene mutations that cause McCune-Albright syndrome result in an abnormal version of the G protein that causes the adenylate cyclase enzyme to be constantly turned on (constitutively activated). Constitutive activation of the adenylate cyclase enzyme leads to over-production of several hormones, resulting in the abnormal bone growth, unusual skin pigmentation, and endocrine problems that occur in McCune-Albright syndrome.
McCune-Albright syndrome is not inherited. Instead, it is caused by a random mutation in the GNAS gene that occurs very early in development. As a result, some of the body's cells have a normal version of the GNAS gene, while other cells have the mutated version. This phenomenon is called mosaicism. The severity of this disorder and its specific features depend on the number and location of cells that have the mutated GNAS gene.
People normally inherit one copy of each gene from their mother and one copy from their father. For most genes, both copies are active, or "turned on," in all cells. For a small subset of genes, however, only one of the two gene copies is active. For some of these genes, only the copy inherited from a person's father (the paternal copy) is active, while for other genes, only the copy inherited from a person's mother (the maternal copy) is active. These differences in gene activation based on the gene's parent of origin are caused by a phenomenon called genomic imprinting.
The GNAS gene has a complex genomic imprinting pattern. In some parts of the body the maternal copy of the gene is active, while in others the paternal copy is active. Progressive osseous heteroplasia is caused by certain mutations that affect the paternal copy of the gene. These mutations disrupt the function of the G protein and impair its ability to regulate osteogenesis. Impaired regulation of osteogenesis results in the ectopic production of bony tissue in the skin and muscles seen in progressive osseous heteroplasia.
Mutations in the GNAS gene also cause Albright hereditary osteodystrophy (AHO), which is characterized by short stature, obesity, unusually short fingers and toes (brachydactyly), ectopic development of bony tissue under the skin, and other skeletal abnormalities. When a mutation that causes AHO is inherited from a person's mother, the affected individual will usually have AHO accompanied by a resistance to multiple hormones (a condition called pseudohypoparathyroidism type Ia, or PHPIa). A paternally-inherited mutation can result in AHO without endocrine problems; this form of the condition is also called pseudopseudohypoparathyroidism (PPHP).
Some gene mutations are acquired during a person's lifetime and are present only in certain cells. These changes, which are called somatic mutations, are not inherited. Somatic mutations in the GNAS gene have been found in tumors of the endocrine glands and in fibrous lesions (dysplasia) that can occur in bones. These mutations are believed to result in an overactive G protein, which triggers abnormal cell growth. Because the cells with mutations are not as widespread in the body as in McCune-Albright syndrome, the abnormal growth is confined to a particular gland or fibrous lesion.
Cytogenetic Location: 20q13.3
Molecular Location on chromosome 20: base pairs 57,414,794 to 57,486,249
The GNAS gene is located on the long (q) arm of chromosome 20 at position 13.3.
More precisely, the GNAS gene is located from base pair 57,414,794 to base pair 57,486,249 on chromosome 20.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
You and your healthcare professional may find the following resources about GNAS helpful.
You may also be interested in these resources, which are designed for genetics professionals and researchers.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
adrenal glands ; brachydactyly ; cell ; constitutive ; dysplasia ; ectopic ; enzyme ; gene ; guanine ; imprinting ; lesion ; locus ; maternal ; mosaicism ; mutation ; nucleotide ; osteogenesis ; pigmentation ; pituitary gland ; protein ; short stature ; signal transduction ; skin pigmentation ; stature ; subunit ; syndrome ; testes ; thyroid ; tissue ; transduction
You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).
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.