Updated: Mar 13, 2008
In 1937, McCune-Albright syndrome (MAS) was described as the triad of café au lait macules (CALMs), polyostotic fibrous dysplasia (PFD), and endocrine dysfunction with precocious puberty. Mutations of Gs-alpha residues involved in the GTPase reaction that result in constitutive activation are present in persons with MAS.1
The mutation leads to aberrant Gs protein alpha-subunit coupling 7-transmembrane-domain receptors to adenylate cyclase, resulting in constitutive adenylate cyclase activation and cAMP overproduction.2 The long-term effect of these mutations is based on a population of mutated multipotent postnatal skeletal stem cells (mesenchymal stem cells). These stem cells underlie the formation of abnormal bone and a fibrotic marrow in fibrous dysplasia.3
MAS is related to Albright hereditary osteodystrophy (AHO), and heterozygous inactivating Gs-alpha mutations result in AHO.1 Gs-alpha is imprinted in a tissue-specific fashion. It is primarily expressed from the maternal allele in the renal proximal tubules, the thyroid, the pituitary, and the ovaries.1 Maternally inherited mutations result in AHO plus parathyroid hormone, thyrotropin, and gonadotropin resistance (pseudohypoparathyroidism type 1A). On the other hand, paternally inherited mutations result in AHO alone.1
Other eMedicine articles include McCune-Albright Syndrome (endocrinology focus) and McCune-Albright Syndrome (pediatric focus). A Medscape CME course that may be of interest is Genetics of Adrenal Tumors Associated With Cushing's Syndrome: A New Classification for Bilateral Adrenocortical Hyperplasias.
Girls with MAS have gonadotropin-independent precocious puberty related to estrogen secretion from ovarian cysts. The most widely accepted hypothesis is that a spontaneous mutation in early embryogenesis leads to a mosaic pattern of autonomously functioning clones of cells in the affected child's organs (eg, ovarian cysts). The proposed mutation is in the GNAS1 gene coding for the signal-transducing guanine nucleotide-binding protein G-alpha subunit (protein Gs). This membrane-bound protein has a role in regulating the adenylate cyclase system.
In normal hormone-sensitive cells, such as endocrine cells, the Gs protein transmits messages from hormone receptors to intracellular targets. A stimulatory hormone (eg, thyrotropin) binds to a receptor on the cell surface coupled to the Gs protein, activating the Gs protein and stimulating cellular adenylate cyclase to produce elevated levels of cyclic adenosine monophosphate, which, in turn, stimulates hormone production and cell proliferation in targeted endocrine cells (eg, thyroxine production).
In several patients with MAS, investigators have found a substitution for arginine-201 with cystine or histidine in the alpha subunit of protein G, causing a gain of function with the protein in the activated state and constitutive activation of adenylyl cyclase in the absence of any stimulatory hormone. This mutation has been found in cells from ovarian cysts, CALMs, and PFD bony lesions in patients with MAS. Such a mutation in the germline is thought to be lethal; therefore, only the mosaic phenotype is observed.
Researchers have isolated activating mutations of GNAS1 in pituitary adenomas, thyroid adenomas, ovarian cysts, monostotic bone dysplasia, and the adrenal glands.4 GNAS1 gene abnormality in pseudohypoparathyroidism I-a has also been noted.5
The frequency is unknown.
From 1966-1995, 158 cases have been documented in the literature.
Although 2 long-term follow-up studies have shown no increased risk of premature death, several authors have noted unexplained sudden death in patients with a severe phenotype. Patients may have multiple endocrine, cardiac, GI, central nervous system, hematopoietic, and hepatic manifestations, all of which can contribute to significant morbidity.
One study of 16 girls and 10 boys with MAS and found that (1) MAS occurs slightly more frequently in girls than in boys, (2) peripheral precocious puberty (PPP) in MAS occurs significantly more frequently and at a younger age in girls than in boys, (3) PPP in boys with MAS correlates with bilateral testicular enlargement, (4) monolateral macroorchidism can occur, and (5) testicular microlithiasis might function as another marker for MAS in males.6
A male-to-female ratio of 1:2 has been reported. The fact that girls develop precocious puberty far more frequently than boys (9:1 female-to-male ratio) probably explains why this autosomal mutation is recognized more frequently in girls than in boys.
MAS manifests in childhood, with the mean onset of precocious puberty (the usual presenting sign) at 4.9 years (range 0.3-9 y).
Patients with MAS can present with a variety of bone, skin, and endocrine pathology.
MAS is caused by a sporadic, early postzygotic somatic mutation in the GNAS1 gene at locus 20q13.1-13.2, coding for G protein subunit, Gs-alpha.
Café au lait macules
Neurofibromatosis type I or IISkin biopsy of CALMs reveals hyperpigmentation of the epidermis, with a normal number of melanocytes. While some specimens show giant melanosomes, this is by no means diagnostic. Giant melanosomes can also be found in CALMs of patients with neurofibromatosis and in healthy patients.
The bone histology of MAS has been reassessed in view of the pathological effect of the genetic lesions on mutated skeletal stem cells. MAS is a disease of excess abnormal and imperfect bone formation, a fact which helps elucidate its mechanisms.24
Medical treatment is only partially effective and transsphenoidal surgery remains difficult secondary to massive thickening of the skull base. Radiotherapy is contraindicated because of the possibility of sarcomatous transformation.21 Their puberty does not generally respond to gonadotropic-releasing hormone agonists, and short-acting aromatase inhibitors have had limited effectiveness. Bromocriptine, cabergoline, and octreotide or a combination of these has demonstrated inconsistent results; pegvisomant, a GH receptor antagonist, is a possibility, although it has not yet been used as a treatment for MAS with GH pathology.21
Ovarian cysts occur frequently in females with PPP with MAS.29 Surgery remains an option for the evaluation and treatment of cysts.
A variety of medications may be required to correct various endocrine and metabolic derangements. Some of these include medroxyprogesterone acetate, testolactone, bromocriptine, propylthiouracil, ergocalciferol, and calcitonin. A qualified endocrinologist should conduct therapy.
Feuillan et al31 reported on a pilot study of letrozole treatment for precocious puberty in girls with the MAS. Bisphosphonate therapy may have a role in the treatment of fibrous dysplasia.32 Somatostatin analogs are useful in some, but not all, cases. The GH receptor antagonist pegvisomant can be useful in normalizing insulinlike growth factor-I levels.2
Given to correct endocrine disorders associated with sexual precocity manifestations (98% of cases), such as pubarche, menarche, and thelarche.
Progestins stop endometrial cell proliferation, allowing organized sloughing of cells after withdrawal. Typically does not stop acute bleeding episode but produces normal bleeding episode following withdrawal.
10 mg PO qd; adjust to effect
Not recommended
May decrease effects of aminoglutethimide
Documented hypersensitivity; cerebral apoplexy; undiagnosed vaginal bleeding; thrombophlebitis; liver dysfunction
X - Contraindicated; benefit does not outweigh risk
Caution in asthma, depression, renal or cardiac dysfunction, or thromboembolic disorders
Synthetic peripheral aromatase inhibitor that blocks production of estradiol and estrone from testosterone and androstenedione.
250 mg PO qid; adjust to effect
Not established
Need to monitor INR closely in patients taking warfarin and possibly adjust dose
Documented hypersensitivity; males with breast cancer
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Monitor liver function; edema may develop in patients with congestive heart failure, liver, or renal insufficiency; may worsen hypertension; may exacerbate epilepsy and migraine
Some agents have dopaminergic properties that inhibit prolactin secretion.
Semisynthetic ergot alkaloid derivative; strong dopamine D2-receptor agonist; partial dopamine D1-receptor agonist; indicated for amenorrhea/galactorrhea secondary to hyperprolactinemia in the absence of primary tumor.
10-40 PO mg/d; not to exceed 100 mg/d
Not established
Toxicity may increase with ergot alkaloids; amitriptyline, butyrophenones, imipramine, methyldopa, phenothiazines, and reserpine may decrease effects
Documented hypersensitivity; ischemic heart disease; peripheral vascular disorders
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in renal or hepatic disease
Used in the palliative treatment of hyperthyroidism.
Derivative of thiourea that inhibits organification of iodine by thyroid gland. Blocks oxidation of iodine in thyroid gland, thereby inhibiting thyroid hormone synthesis; inhibits T4 to T3 conversion (advantage over other agents).
Initial dose: 300 mg/d PO divided tid
Severe hyperthyroidism: 600-1200 mg/d PO
Maintenance dosing: 100-150 mg PO divided tid
<6 years: Not established
6-10 years: 50-150 mg/d PO initially
>10 years: 150-300 mg/d PO initially
Alternatively, 5-7 mg/kg/d or 150-200 mg/m2/d PO divided q8h; subsequent dosing determined by response
PTU has antivitamin K activity; may potentiate activity of oral anticoagulants
Documented hypersensitivity; breastfeeding women
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Monitor PT during therapy; may cause hypoprothrombinemia and bleeding; once symptoms of hyperthyroidism have resolved, lower maintenance dose if serum thyrotropin levels are elevated
Agents (eg, vitamin D) are indicated to correct deficiencies leading to hypoparathyroidism. Agents (eg, calcitonin) are indicated to treat hypercalcemia and prevent bone loss.
Stimulates absorption of calcium and phosphate from small intestine and promotes release of calcium from bone into blood.
625 mcg to 5 mg/d (25,000-200,000 U) PO
1.25-5 mg/d (50,000–200,000 U) PO
Colestipol, mineral oil, and cholestyramine may decrease absorption of ergocalciferol from small intestine; thiazide diuretics may increase effects of vitamin D
Documented hypersensitivity; hypercalcemia; malabsorption syndrome
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Caution in impaired renal function, renal stones, heart disease, or arteriosclerosis
Lowers elevated serum calcium level in patients with primary hyperparathyroidism. Expect a higher response when serum calcium levels are high. Onset of action is approximately 2 h following injection and activity lasts for 6-8 h. May lower calcium levels for 5-8 d by approximately 9% if given q12h. IM route is preferred at multiple injection sites with dose >2 mL.
4 IU/kg IM/SC q12h
Increase dose to 8 IU/kg q12h if response not satisfactory after 1-2 d and 8 IU/kg q6h if response remains unsatisfactory >2 d
Not established
None reported
Documented hypersensitivity
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Hypocalcemia may occur; examine urine sediment during prolonged therapy
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McCune-Albright syndrome, Albright's syndrome, café au lait macules, CALMs, cafe au lait macules, cafe-au-lait macules, polyostotic fibrous dysplasia, PFD, endocrine dysfunction, precocious puberty, MAS, PPP
Noah S Scheinfeld, MD, JD, FAAD, Assistant Clinical Professor, Department of Dermatology, Columbia University; Consulting Staff, Department of Dermatology, St Luke's Roosevelt Hospital Center, Beth Israel Medical Center, New York Eye and Ear Infirmary; Private Practice
Noah S Scheinfeld, MD, JD, FAAD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Optigenex Consulting fee Independent contractor
D Stanton Whittaker Jr, MD, Consulting Staff, Boone Dermatology Clinic
D Stanton Whittaker Jr, MD is a member of the following medical societies: Phi Beta Kappa
Disclosure: Nothing to disclose.
Eleanor E Sahn, MD, Director, Division of Pediatric Dermatology, Associate Professor, Departments of Dermatology and Pediatrics, Medical University of South Carolina
Eleanor E Sahn, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, and Southern Medical Association
Disclosure: Nothing to disclose.
Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.
Van Perry, MD, Assistant Professor, Department of Medicine, Division of Dermatology, University of Texas Health Science Center
Van Perry, MD is a member of the following medical societies: American Academy of Dermatology and American Society for Laser Medicine and Surgery
Disclosure: Nothing to disclose.
Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University
Catherine Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.
Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.
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