McCune-Albright syndrome

Background

McCune-Albright syndrome (MAS) is a rare condition that was first described in 1937. It is sometimes called Albright syndrome.

The classic triad consists of 3 features:

Patchy skin pigmentation
Bone abnormalities
Endocrine (hormonal) abnormalities, in particular early puberty

At least 2 of these features need to be present to diagnose the condition. MAS is caused by a spontaneous (chance) mutation in the GNAS1 gene. This gene then forms an abnormal protein that regulates cell proliferation, migration and survival. The mutation occurs early in the development of an embryo and affects only a subset of the patient's cells (called mosaicism). The mutation cannot be passed on to affected patient's children.

Clinical features

1. Patchy skin pigmentation	Seen in approximately 60% of patients, Often the first sign of this disorder as present at birth or noted during the first few months of life. Distinct shape and distribution: often large (segmental) and with jagged borders (unlike the smaller café-au-lait macules (CALM) with smooth borders seen in neurofibromatosis), rarely extend over the midline and most are on the side overlying the bone defects. May follow the lines of Blaschko.
2. Bone abnormalities	Fibrous dysplasia of bones (polyostotic fibrous dysplasia); normal bone is replaced by fibrous tissue and weakened bone. Usually develop during the first ten years of life, and progress until early adulthood and then become relatively stable.. The femur (long leg bone) and pelvis (hip bone) are the most common bones involved, and X-rays show lytic lesions with scalloped borders and a “ground glass” pattern. May cause recurrent fractures, bone pain, facial asymmetry, scoliosis (abnormal curvature of the spine), unequal leg length, limb bowing, or a limp.
3. Endocrine abnormalities	These are characterised by overactive hormones. The most common endocrine abnormality in MAS is early puberty; the average age of onset is around 5 years. Girls are more commonly affected than boys. Early puberty in girls is due to high levels of oestradiol produced by ovarian tissue. MAS is also associated with hyperthyroidism, growth hormone excess (acromegaly), Cushing syndrome, breast discharge due to excess prolactin hormone, and renal phosphate wasting (excess urinary excretion of phosphate, which may result low circulating phosphate in the blood).
4. Other associated problems	MAS has been associated with a variety of other clinical problems including: Developmental delay Liver disease and jaundice High blood pressure and abnormal heart rhythms

Diagnosis

X-rays of the affected bones show characteristic features such as a central ‘ground-glass’ pattern, lytic lesions (local disappearance of normal bone), cyst-like appearance, and evidence of current or past fractures.
CT, MRI, and nuclear medicine bone scanning may also be useful.
Once the condition has been diagnosed, other investigations are required to screen for occult (concealed) endocrine abnormalities.
Genetic testing is possible, but is not routinely available.

Treatment

Medical treatment of MAS has had mixed success.
Early puberty can be treated with various hormonal agents, but results have been inconsistent.
Bisphosphonate medicines have recently been used to reduce fracture rates and bone pain in patients with MAS. However, results have again been inconsistent.
Other endocrine problems require specific medication or surgery.

Complications

Bony changes in the skull can result in damage to nerves causing vision and/or hearing loss.
Bony changes in the chest wall may lead to difficulty breathing.
A type of bone cancer called osteosarcoma develops in up to 2% of patients with MAS. This tumour is found most often in patients who have received radiation treatment to affected bone lesions.
Although 2 long-term studies have shown no increased risk of premature death, several authors have noted unexplained sudden death in patients with severe features of the disease.

Related information

References:

McCune-Albright Syndrome – eMedicine dermatology, pediatric diseases
Albright Syndrome – eMedicine pediatrics, general medicine
McCune-Albright Syndrome – eMedicine endocrinology
Dumitrescu CE, Collins MT. McCune-Albright syndrome. Orphanet J Rare Dis. 2008; 3: 12.
Roth JG, Esterly NB. McCune-Albright syndrome with multiple bilateral café au lait spots. Pediatr Dermatol. 1991 Mar;8(1):35-9.
HURWITZ CLINICAL PEDIATRIC DERMATOLOGY A Textbook of Skin Disorders of Childhood and Adolescence THIRD EDITION Amy S Paller MD Anthony J Mancini MD ELSEVIER SAUNDERS
Claudia E Dumitrescu and Michael T Collins. McCune-Albright syndrome. Orphanet Journal of Rare Diseases 2008, 3:12 doi:10.1186/1750-1172-3-12

On DermNet NZ:

Congenital melanocytic naevi (brown birthmarks)

Other websites:

McCune-Albright Syndrome – Medline Plus
McCune-Albright syndrome US National Library of Medicine Genetics Home Reference
McCune-Albright Syndrome – OMIM
McCune-Albright Syndrome – National Institute of Child Health and Human Development
Medscape Reference:

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Author: Dr Marie Hartley, Staff Writer.