What is McCune Albright Syndrome?
McCune Albright Syndrome is a combination of disorders occur in the skin, skeletal system and hormone producing glands or associated tissues. This syndrome is a rare genetic disorder with three classic features. The included clinical presentations are related to inconsistent skin pigmentation, bone structural abnormalities and hormonal abnormalities, especially early puberty. All the related symptoms may or may not present in every case, but combination of two related abnormalities are considered as presence of McCune Albright Syndrome1,2,3.
Depending upon clinical features the symptoms are classified into four major subgroups. They are as follows:
Light brown patches on the skin, usually may present from birth or appear within first few months after birth. These spots have irregular borderline and large in size. Some of the spot marks also have smooth borders and small sized.
The irregular borders are often compared to a map of the coast of Maine, whereas smooth borders, which are compared to the coast of California. The spots are usually distributed on the side overlying the bone defects and rarely present at midline. Almost 60% affected individuals are having this symptom.
Polyostotic Fibrous Dysplasia
Polyostotic fibrous dysplasia is an abnormal fibrous tissue present in the bone of the affected individual. The symptom is denoted as Polyostotic, as the fibrous tissue distributed in many bones. Structural abnormality, uneven growth, and frequent fractures are common symptoms associated with replacement of bones with fibrous tissue.
Depending upon the site, bone deformity causes structural abnormalities, like lesion affected skull or jaw bone causes uneven growth of the face. Lesion in the vertebral column causes scoliosis (abnormal curving of the spinal cord). Bone lesions can be cancerous, but it can happen with only 1% of the affected individual.
Over-activation of certain endocrine gland causes stimulation of hormonal activities, which lead to several hormonal abnormalities. The resulting of this causes early puberty, hyperthyroidism, overproduction of growth hormone causes acromegaly, Cushing syndrome due to over activity of the adrenal gland, excessive prolactin hormone secretion leads to breast discharge, excess urinary excretion of phosphate (renal phosphate wasting) may cause insufficient phosphate in the circulating blood. Early puberty mainly occurs at age of 5 years or before in girls. The early puberty related symptoms are more prominent in girl child than boys. Early onset of menstruation cycle is due to excess estrogen hormone secretion.
Apart from above mentioned three major clinical symptoms, other associated problems in McCune Albright Syndrome affected individuals have delayed development, hepatic disorders and jaundice, hypertension and abnormal heart rhythm2,3,4.
McCune Albright Syndrome is caused by a somatic mutation in the GNAS1 gene. This disease is not inherited. The syndrome is developed at the stage of embryo formation as mosaicism (a subset of the patient’s cells) get affected. The GNAS1 gene synthesizes an abnormal protein that regulates proliferation, migration, and survival of cells.
This abnormal cellular regulation is due to irregular hormonal activity, which leads to stimulation of enzyme adenylate cyclase activity for prolong period. The resultant of these over production of certain hormones and causes onset of McCune Albright Syndrome. The abnormality of genetic mutation is random. There is no clinical history of the hereditary transmission of the syndrome.
The abnormal genetic mutation does not occur in the sperm or egg, but that acquired after conception. The abnormal GNAS1 gene mutation is not distributed in a similar pattern in every cell, therefore some are cells have normal GNAS gene, whereas others are abnormal mutated GNAS1 gene. This incident is called mosaicism2,3,5.
The diagnosis of McCune Albright Syndrome can be conducted by radiography, biopsy, genetic testing and hematological testing.
- Fibrous dysplasia of bone is easily diagnosed by plain radiography.
- The most sensitive diagnostic tool to detect the presence of Fibrous dysplasia of bone is isotopic bone scans. This radiography can be utilized for the initial evaluation of the disease extension and possible associated functional abnormalities.
- The best imaging tool to diagnose Fibrous dysplasia lesions is computed tomography (CT) scanning. CT scan usually performs to reveal the abnormality in the skull, which causes “ground glass” appearance. The nature of the findings is not same for both children or young aged affected patient and elderly patients. The CT scan findings disclose homogeneous lesions in children and young adults, whereas both homogeneous and “cystic” lesions are present in older aged patients6.
Any abnormal findings of the radiology require conducting biopsy test. For a biopsy, the sample of lesions collected to diagnose under a microscope for determination of malignant cell growth6.
Genetic testing may not contribute completely in the management of the McCune Albright Syndrome, as the somatic mosaic characteristic of the syndrome may provide a negative result, but that does not mean that abnormal genetic mutation is absent6.
A different laboratory test of blood is performed to check the hormone level in the plasma. This helps to prepare a treatment plan3.
McCune Albright Syndrome is a non-curable disease. The multidisciplinary expert team works together to manage the associated symptoms.
- Medicine are prescribed to treat different hormone related disorders.
- Surgical intervention is also recommended for management of the orthopedic complications3.
The treatment prognosis of McCune Albright Syndrome is not same for every individual. It depends on the severity of the symptoms. Therapeutic treatment is effective to regulate the hormonal problems. Progressive fibrous dysplasia affects late childhood and gradually extended throughout the life. Restricted locomotion, facial deformity, vision loss, hearing difficulty etc may arise due to extensive bone disease 2, 5.
- Gabriel I Uwaifo; McCune-Albright Syndrome; Online available at http://emedicine.medscape.com/article/127233-overview
- McCune-Albright syndrome, Genetic Home References; Online available at https://ghr.nlm.nih.gov/condition/mccune-albright-syndrome
- McCune-Albright syndrome; Genetic and Rare Disease Information Center;
- Online available at https://rarediseases.info.nih.gov/diseases/6995/mccune-albright-syndrome
- Dr Marie Hartley, Staff Writer, McCune-Albright syndrome; DermNet New Zealand; Online available at http://www.dermnetnz.org/topics/mccune-albright-syndrome/
- McCune Albright Syndrome; National Organization for Rare Disorders; Online available at https://rarediseases.org/rare-diseases/mccune-albright-syndrome/
- Claudia E Dumitrescu, Michael T Collins; McCune-Albright syndrome; Orphanet Journal of Rare Diseases20083:12; DOI: 10.1186/1750-1172-3-12 ; Online available at https://ojrd.biomedcentral.com/articles/10.1186/1750-1172-3-12