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Reviewed January 2009
What is McCune-Albright syndrome?
McCune-Albright syndrome is a disorder that affects the bones, skin, and several hormone-producing (endocrine) tissues.
People with McCune-Albright syndrome develop areas of abnormal scar-like (fibrous) tissue in their bones, a condition called polyostotic fibrous dysplasia. Polyostotic means the abnormal areas (lesions) may occur in many bones; often they are confined to one side of the body. Replacement of bone with fibrous tissue may lead to fractures, uneven growth, and deformity. When lesions occur in the bones of the skull and jaw it can result in uneven (asymmetric) growth of the face. Asymmetry may also occur in the long bones; uneven growth of leg bones may cause limping. Abnormal curvature of the spine (scoliosis) may also occur. Bone lesions may become cancerous, but this happens in fewer than 1 percent of people with McCune-Albright syndrome.
In addition to bone abnormalities, affected individuals usually have light brown patches of skin called café-au-lait spots, which may be present from birth. The irregular borders of the café-au-lait spots in McCune-Albright syndrome are often compared to a map of the coast of Maine. By contrast, café-au-lait spots in other disorders have smooth borders, which are compared to the coast of California. Like the bone lesions, the café-au-lait spots in McCune-Albright syndrome often appear on only one side of the body.
Girls with McCune-Albright syndrome usually reach puberty early. These girls usually have menstrual bleeding by age two, many years before secondary sex characteristics such as breast enlargement and pubic hair are evident. This early onset of menstruation is believed to be caused by excess estrogen, a female sex hormone, produced by cysts that develop in one of the ovaries. Less commonly, boys with McCune-Albright syndrome may also experience early puberty.
Other endocrine problems may also occur in people with McCune-Albright syndrome. The thyroid gland, a butterfly-shaped organ at the base of the neck, may become enlarged (a condition called a goiter) or develop masses called nodules. About 50 percent of affected individuals produce excessive amounts of thyroid hormone (hyperthyroidism), resulting in a fast heart rate, high blood pressure, weight loss, tremors, sweating, and other symptoms. The pituitary gland (a structure at the base of the brain that makes several hormones) may produce too much growth hormone. Excess growth hormone can result in acromegaly, a condition characterized by large hands and feet, arthritis, and distinctive facial features that are often described as "coarse." Rarely, affected individuals develop Cushing's syndrome, an excess of the hormone cortisol produced by the adrenal glands, which are small glands located on top of each kidney. Cushing's syndrome causes weight gain in the face and upper body, slowed growth in children, fragile skin, fatigue, and other health problems.
How common is McCune-Albright syndrome?
McCune-Albright syndrome occurs in between 1 in 100,000 and 1 in 1,000,000 people worldwide.
What genes are related to McCune-Albright syndrome?
McCune-Albright syndrome is caused by a mutation in the GNAS gene. The GNAS gene provides instructions for making one part of a protein complex called a guanine nucleotide-binding protein, or a G protein.
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. GNAS gene mutations that cause McCune-Albright syndrome result in a 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 signs and symptoms of McCune-Albright syndrome.
Read more about the GNAS gene.
How do people inherit 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.
Where can I find information about diagnosis or management of McCune-Albright syndrome?
These resources address the diagnosis or management of McCune-Albright syndrome and may include treatment providers.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about McCune-Albright syndrome?
You may find the following resources about McCune-Albright syndrome helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for McCune-Albright syndrome?
What if I still have specific questions about McCune-Albright syndrome?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding McCune-Albright syndrome?
adrenal glands ; arthritis ; cell ; constitutive ; cysts ; dysplasia ; enzyme ; gene ; goiter ; growth hormone ; guanine ; hormone ; hyperthyroidism ; inherited ; kidney ; menstruation ; mosaicism ; mutation ; nucleotide ; pituitary gland ; protein ; puberty ; scoliosis ; sex hormone ; signal transduction ; syndrome ; thyroid ; tissue ; transduction
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (5 links)
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? in the Handbook.