McCune-Albright syndrome (cont.)
Some children with McCune-Albright syndrome have very low levels of phosphorus in their blood due to excessive losses of phosphate in their urine. This may cause bone changes associated with rickets, and may be treated with oral phosphates and supplemental vitamin D.
- Bone Disease -- Polyostotic Fibrous Dysplasia
The term "polyostotic fibrous dysplasia" means "abnormal fibrous tissue growth in many bones." Normal bone is replaced by irregular masses of fibroblast cells. When this occurs in weight-bearing bones, such as the femur (upper leg bone), limping, deformity, and fractures may occur. In many children, the arms and/or legs are of unequal length, even in the absence of actual fracture. Regions of fibrous dysplasia are also very common in the bones that form the skull and upper jaw. If these areas begin to expand, skull and facial asymmetry may result.
Polyostotic fibrous dysplasia can often be seen in a plain X-ray picture of the skeleton. A more sensitive method of finding lesions is a bone scan, in which a small amount of radioactivity (an isotope of technetium) is injected into a vein, taken up by the abnormal tissues, and detected by a scanner.
Some children may be minimally affected, with no asymmetry, deformity or fracture, and lesions detected only by a bone scan. In a few children, lesions are found only in the base of the skull. By repeating bone scans at intervals of 1 to 2 years, it has been shown that the bone disease in some children may become more extensive over time. Unfortunately, severe bone disease can have permanent effects upon physical appearance and mobility.
There is no known hormonal or medical treatment effective in controlling progressive polyostotic fibrous dysplasia. Surgical procedures to correct fracture and deformity include grafting, pinning, and casting. Skull and jaw changes are often corrected surgically, with great improvement in appearance. Treatment and therapy for this bone disease is usually the most difficult aspect of caring for a child who has severe polyostotic fibrous dysplasia.
- Skin Abnormalities
The irregular, flat areas of increased skin pigment in McCune-Albright syndrome are called "cafe-au-lait" spots because, in children with light complexions, they are the color of coffee with milk. In dark skinned individuals, these spots may be difficult to see. Most children have the pigment from birth, and it almost never becomes more extensive. The pattern of the pigment distribution is unique, often starting or ending abruptly at the midline on the abdomen in front or at the spine in back. Some children have no cafe-au-lait pigment at all; in a few, it is confined to small areas, such as the nape of the neck or crease of the buttocks. There are seldom any medical problems associated with the areas of cafe-au-lait pigment. Some adolescent children may want to use makeup to obscure areas of dark pigment on the face.
There is no way to accurately predict how severe the disease may become in an affected child. There are no reported cases of any parent being affected, and the children of women with McCune-Albright syndrome are normal. All races appear to be affected equally.
The mystery of the cause of the McCune Albright syndrome appears to have been solved by the identification of activating mutations in the GNAS1 gene. The activating mutations render the GNAS1 gene functionally constitutive, turning the gene irreversibly on, so it is constantly active. This occurs in a mosaic pattern, in some tissues and not others.
The syndrome was first described independently in the 1930s by the American pediatrician Donovan James McCune (1902-1976) and a team from the Massachusetts General Hospital in Boston led by the great endocrinologist Fuller Albright (1900-1969):
Last Editorial Review: 8/28/2013
- D. J. McCune: Osteitis fibrosa cystica: the case of a nine year old girl who also exhibits precocious puberty, multiple pigmentation of the skin and hyperthyroidism. American Journal of Diseases of Children, 1936, 52: 743-747.
- F. Albright, A. M. Butler, A. O. Hampton, P. H. Smith: Syndrome characterized by osteitis fibrosa disseminata, areas of pigmentation and endocrine dysfunction, with precocious puberty in females. Report of five cases. New England Journal of Medicine, 1937, 216: 727-746.