McCune-Albright syndrome

The diagnosis of McCune-Albright syndrome (MAS) can be made in people who have two or more of the following typical clinical features of MAS:^[1]

• Café-au-lait skin spots with characteristic features (jagged, irregular borders; distribution respecting the midline of the body; and following the developmental lines of Blaschko)
• Polyostotic fibrous dysplasia (involving more than one bone) or GNAS mutation-proven monostotic fibrous dysplasia (involving a single bone)
• Any of the following endocrine abnormalities (each with specific characteristics):
  • gonadotropin-independent precocious puberty
  • testicular lesions
  • thyroid lesions
  • growth hormone excess
  • phosphate wasting
  • neonatal hypercortisolism (Cushing's syndrome)

MAS may be suspected at birth based upon identifying the characteristic cafe-au-lait spots. However, in many cases, it may not be suspected until late infancy or childhood when precocious (very early) puberty develops or when bone deformities become obvious.^[2]

In cases when only one bone has fibrous dysplasia and there are not other symptoms  genetic testing is needed to establish the diagnosis.^[1]

McCune-Albright syndrome (MAS) is usually a clinical diagnosis, which means that specific signs and symptoms must be present before the diagnosis can be made. If MAS is suspected, various tests may be considered to look for the presence of additional signs and symptoms that may confirm the diagnosis. Tests that may be considered include:

• endocrine studies
• imaging studies including x-ray, ultrasound, CT scan, MRI, and/or radionuclide bone scanning
• blood and urine tests
• bone biopsy or soft-tissue biopsy^[3]

While genetic testing for MAS is available, the ability to detect a mutation depends on the level of mosaicism in the tissue, and the sensitivity of the technique used. In the absence of the clinical criteria needed for a diagnosis, genetic testing may detect a mutation. However, because of the somatic mosaic nature of the disease (the mutation only being present in some cells and tissues), a negative result from readily available (but unaffected) tissue does not exclude the presence of the mutation elsewhere in the body.^[4]

Unfortunately, it is often not possible to determine how severely a person will be affected when a diagnosis is first suspected or confirmed. For this reason, it is important to be aware of the various tissues that can be (or become) involved, and then to screen for involvement.^[4]