McCune Albright Syndrome (MAS)

What is McCune Albright syndrome (MAS)?

McCune Albright syndrome (MAS) is an extremely rare disorder that classically affects the skin, bones, and endocrine system of affected individuals. Specifically, MAS is characterized by fibrous dysplasia (bone that is replaced by abnormal scar-like connective tissue) that weakens the bone, making it abnormally fragile and prone to fracture and causing pain in the affected areas.

In addition, MAS has the following two hallmark findings:

Patches of abnormal skin pigmentation
Multiple endocrine dysfunction

What causes McCune Albright syndrome (MAS)?

MAS is the result of a genetic change in the GNAS1 gene, which in turn triggers an overproduction of a molecule known as cyclic adenosine monophosphate (cAMP). This molecule is involved in various chemical processes of the body, and its overproduction contributes to the development of MAS symptoms.

This mutation occurs spontaneously after fertilization, for no particular reason and in only some of the body’s cells (mosaic pattern). Thus, the symptoms and their severity vary greatly from person to person.

What are the symptoms of McCune Albright syndrome (MAS)?

The hallmark symptom of MAS present in the skin are areas of light-brown skin (i.e. “café au lait spots”) with jagged borders.

The symptoms of MAS present in the endocrine system are the following:

Dysfunction of certain glands that regulate the body’s rate of growth, its sexual development, and certain other metabolic functions
- Early onset of puberty
- Mental abnormalities, such as anxiety or fatigue
- Heart palpitations
- Unintended weight loss
- Growth hormone excess, or acromegaly

The symptoms of MAS present in the bones (most commonly, the long bones of the arms and legs, the bones of the face and skull, and the ribs) are the following:

Bone fractures
Bowed long bones
Abnormal gait
Facial asymmetry, such as uneven jaws
Misaligned or displaced teeth

How is McCune Albright syndrome (MAS) diagnosed?

A diagnosis of MAS may be suspected at birth based on an identification of café au lait skin pigmentations. However, in most cases, MAS is not confirmed until childhood when either precocious puberty develops or when bone deformities become obvious. Aiding in the diagnosis are specialty tests, such as MRI and CT scans, X-rays, a bone scintigraphy, and molecular genetic testing using polymerase chain reaction (PCR) to photocopy and carefully analyze the patient’s DNA.

What are the available treatments for McCune Albright syndrome (MAS)?

Fibrous dysplasia associated with MAS can be treated with drugs called bisphosphonates, such as pamidronate or alendronate, physical therapy, or surgery. The endocrine dysfunction in MAS patients can be treated with a gonadotropin-releasing hormone to decrease the amount of hormones released by the pituitary gland, thus blocking the advancement of precocious puberty, or a growth hormone inhibitor to treat growth hormone excess.

Other treatment of McCune-Albright syndrome is symptomatic and supportive, since there is no cure currently available for the condition.