Severe endocrine and nonendocrine manifestations of the McCune-Albright syndrome associated with activating mutations of stimulatory G protein GS

Reproduction of human fibrous dysplasia of bone in immunocompromised mice by transplanted mosaics of normal and Gsalpha-mutated skeletal progenitor cells

We have isolated progenitor cells from the stromal system of the fibrous dysplastic marrow of patients with McCune-Albright Syndrome. Analysis of the Gsalpha gene from individual colonies provided direct evidence for the presence of two different genotypes within single fibrous dysplastic lesions: marrow stromal cells containing two normal Gsalpha alleles, and those containing one normal allele and an allele with an activating mutation. Transplantation of clonal populations of normal cells into the subcutis of immunocompromised mice resulted in normal ossicle formation. In contrast, transplantation of clonal populations of mutant cells always led to the loss of transplanted cells from the transplantation site and no ossicle formation. However, transplantation of a mixture of normal and mutant cells reproduced an abnormal ectopic ossicle recapitulating human fibrous dysplasia and providing an in vivo cellular model of this disease. These results provide experimental evidence for the necessity of both normal and mutant cells in the development of McCune-Albright Syndrome fibrous dysplastic lesions in bone.

Reproductive dysfunction in women with Albright's hereditary osteodystrophy

Most individuals with Albright's hereditary osteodystrophy (AHO) have deficient expression or function of G(s alpha), the alpha subunit of the guanine nucleotide binding protein that stimulates adenylyl cyclase, and are resistant to parathyroid hormone (PTH) and other hormones that act via stimulation of adenylyl cyclase. To determine the incidence and etiology of ovarian dysfunction in women with AHO, we examined the reproductive history and hypothalamic-pituitary-ovarian axis in 17 affected women aged 17-43 yr. All patients had typical PTH resistance and an approximately 50% reduction in erythrocyte G(s alpha) activity, (0.43 +/- 0.03 vs. 0.92 +/- 0.08 for normal control subjects, P < 0.001). Fourteen of the 17 patients (76%) were oligomenorrheic or amenorrheic, more than half had delayed or incomplete sexual development, and only two had a history of earlier pregnancy. Most women were mildly hypoestrogenic, with normal to slightly elevated serum gonadotropin levels. Computer analysis of 24 hour LH measurement showed that the frequency of LH peaks/24 h in AHO women varied widely, but as a group they were not statistically different from a group of normal women studied in the early follicular phase. Administration of 100 microg synthetic GnRH produced normal FSH and LH responses. We conclude that reproductive dysfunction is common in women with AHO and probably represents partial resistance to gonadotropins.

Advances in endocrinology

Molecular genetics will continue to help us to make precise diagnoses. At present, the expertise to achieve this for a specific disease is often exclusive to one unit with a research interest. It will be important to establish a coordinated approach at a supraregional level to provide molecular diagnosis for rare disorders as a fast reliable clinical service. In addition understanding the molecular mechanisms of disease is likely to direct a search for new treatments. For instance, calcium channel blockers have been used in nesidoblastosis to reduce the hypersecretion of insulin, as a result of the recognition of the role that calcium has in the function of the beta-cell ATP sensitive K+ channel. Although the potential benefits of hGH are now being clearly defined in a range of growth disorders, the treatment is invasive and expensive. It is likely that future endocrine therapeutic developments could include slow release growth hormone preparations, orally active growth hormone mimetics, or even hormone production from an ectopic viral cDNA vector. The next "advances in endocrinology" will also reveal whether leptin will have a therapeutic role in appetite control or even the modulation of pubertal development.

Primary hyperparathyroidism-associated polyostotic fibrous dysplasia: absence of McCune-Albright syndrome mutations

Several cases of sporadic primary hyperparathyroidism in association with fibrous dysplasia of the bone have been reported in the English literature. Since fibrous dysplasia is a major feature and hyperparathyroidism is occasionally found in the McCune-Albright syndrome, we hypothesized that such cases may represent a variant of this syndrome. A 28-year-old male had primary hyperparathyroidism associated with polyostotic fibrous dysplasia but no other manifestations of the McCune-Albright syndrome. Genomic DNA samples from his parathyroid adenoma, dysplastic bone sample, and peripheral leukocytes were analyzed for the presence of activating mutations of the stimulating G protein alpha subunit gene (gsp). Allele-specific hybridization revealed the presence of normal sequences only, coding for arginine and glutamine at codons 201 (exon 8) and 227 (exon 9), respectively. Further, single strand conformational analysis of a 224 base pair fragment of exon 8 revealed no conformational aberrations. Furthermore, the sequences of a 164 base pair fragment of exon 8 and a 170 base pair fragment of exon 9 were normal. The results strongly suggest that gsp mutation is absent in affected and normal tissues in this patient and that the association of hyperparathyroidism and fibrous dysplasia may not represent a variant of the McCune-Albright syndrome.

Recurrent ovarian cyst and mutation of the Gs alpha gene in ovarian cyst fluid cells: what is the link with McCune-Albright syndrome?

Isolated peripheral precocious puberty due to recurrent ovarian cysts evokes a McCune-Albright syndrome (MAS). This syndrome associates endocrine dysfunction such as precocious puberty, polyostotic fibrous dysplasia, and "café-au-lait" skin lesions. We report the case of a 3-y-old girl who presented with peripheral puberty with extremely elevated oestradiol level, low LH and FSH levels, and an ovarian cyst that quickly resolved. Skeletal X-rays were normal and she had no café-au-lait spots. GnRH analogue treatment was ineffective. A second ovarian cyst appeared and was completely drained under ultrasonographic guidance. Molecular biological analysis performed on fluid cells revealed the Arg201-->His mutation of the Gs alpha gene described in MAS. Percutaneous aspiration of simple ovarian cyst to detect "MAS" mutation is of interest in the diagnosis of recurrent ovarian cyst.

Polymerase chain reaction-based technique for the selective enrichment and analysis of mosaic arg201 mutations in G alpha s from patients with fibrous dysplasia of bone

Mutations in the arg201 codon of the alpha s G protein-subunit have been associated with a variety of disorders, but analysis of such mutations has been complicated by their mosaic presentation. To overcome the problems associated with the analysis of genomic mutations that may be present in low and variable yield throughout the body, a polymerase chain reaction (PCR)-based technique has been developed that allows the selective amplification of products from the mutant allele. This technique uses site-directed mutagenesis to generate a PCR product from the normal allele that is susceptible to restriction endonuclease digestion, whereas that from the mutant allele is resistant to digestion. Consecutive and repeated cycles of amplification and digestion allow selective enrichment of the product from the mutant allele. The technique has been applied to the analysis of patients with fibrous dysplasia of bone, where the consequence of G alpha s mutations may vary from monostotic to polyostotic lesions, and has been performed with DNA isolated from either bone biopsy specimens or peripheral blood leukocytes. In addition to the previously described arg-->his and arg-->cys substitutions, the analyses have detected a novel arg-->ser substitution in one of the patients. This patient presented with a panostotic disease and may represent a unique subgroup of fibrous dysplasia.

An activating mutation in a Caenorhabditis elegans Gs protein induces neural degeneration

Heterotrimeric guanine nucleotide-binding proteins (G proteins) act as signal-transducing molecules that connect serpentine-transmembrane receptors to a variety of intracellular effectors. We characterized a Caenorhabditis elegans G(s) gene, gsa-1, which encodes a G(s) alpha-subunit (G alpha(s)) that is expressed throughout the nervous system and in muscle cells. gsa-1 is an essential gene; a loss-of-function mutation in gsa-1 results in lethality at the first stage of larval development. Partial (mosaic) loss of G alpha(s) expression or overexpression of the protein results in reciprocal defects in movement and egg-laying, suggesting a role for G alpha(s) in the regulation of these behaviors. Expression of a constitutively active form of G alpha(s) from an inducible promotor results in hypercontraction of body-wall muscle cells and vacuolization and degeneration of neurons within hours of induction. Neurons that are susceptible to the degeneration induced by activated G alpha(s) are predominantly motoneurons located within the ventral nerve cord. Phenotypic analysis shows that the induced neural degeneration is not the result of programmed cell death but is probably caused by the activation of ion channels. A genetic suppressor of activated G alpha(s) was isolated that identifies a putative downstream target of G(s) signaling.

Inborn errors of signal transduction: mutations in G proteins and G protein-coupled receptors as a cause of disease

A vast array of neurotransmitters, polypeptide hormones and other extracellular signalling molecules utilize G protein-coupled pathways for transmembrane signalling. In recent years, mutations in G protein-coupled receptors and in G protein alpha subunits have been identified as the cause of a variety of human diseases. Both loss and gain of function mutations have been described in disorders such as Albright hereditary osteodystrophy, nephrogenic diabetes insipidus, McCune-Albright syndrome, and familial male precocious puberty. Identification of mutations in G protein-coupled receptors and in G proteins in human diseases has provided unique insights into G protein-coupled signal transduction, has important implications for diagnosis and potentially for treatment, and should stimulate the search for additional defects in G protein-coupled signal transduction in other diseases.

Fibrous dysplasia

Fibrous dysplasia provides the orthopedic surgeon with tremendous reconstructive challenges. The manifestations of the condition are very diverse and often involve organ systems not routinely cared for by the orthopedic surgeon. We present a concise review of the radiography, histology, clinical manifestations, and complications of this condition, with the main focus on the non-orthopedic management challenges.

Clinical implications of genetic defects in G proteins. The molecular basis of McCune-Albright syndrome and Albright hereditary osteodystrophy

Inactivating and activating mutations in the gene encoding G alpha s (GNAS1) are known to be the basis for 2 well-described contrasting clinical disorders, Albright hereditary osteodystrophy (AHO) and McCune-Albright syndrome (MAS). AHO is an autosomal dominant disorder due to germline mutations in GNAS1 that decrease expression or function of G alpha s protein. Loss of G alpha s function leads to tissue resistance to multiple hormones whose receptors couple to G alpha s. By contrast, MAS results from postzygotic somatic mutations in GNAS1 that lead to enhanced function of G alpha s protein. Acquisition of the activating mutation early in life leads to a more generalized distribution of the mosaicism and is associated with the classic clinical triad of polyostotic fibrous dysplasia, endocrine hyperfunction, and café au lait skin lesions described in MAS. Acquisition of a similar activating mutation in GNAS1 later in life presumably accounts for the restricted distribution of the gsp oncogene, and is associated with the development of isolated lesions (for example, fibrous dysplasia, pituitary or thyroid tumors) without other manifestations of MAS. Tissues that are affected by loss of G alpha s function in AHO are also affected by gain of G alpha s function in MAS, thus identifying specific tissues in which the second messenger cAMP plays a dominant role in cell growth, proliferation, or function. Further investigations of the functions of G alpha s and other members of the GTPase binding protein family will provide more insight into the pathogenesis and clinical manifestations of human disease.

Increased IL-6-production by cells isolated from the fibrous bone dysplasia tissues in patients with McCune-Albright syndrome

McCune-Albright syndrome (MAS) is characterized by café-au-lait spot, multiple endocrine hyperfunction, and polyostotic fibrous dysplasia. A somatic point mutation of Gsalpha protein was reported to decrease GTPase activity, leading to increase in the GSalpha-associated hormone actions via cAMP. IL-6 is known to stimulate osteoclast formation and in the IL-6 promoter, a cAMP responsive element has been identified. In this paper, we investigated the role of IL-6 in the bone lesions of MAS, using the isolated fibrous cells from the polyostotic fibrous dysplasia tissues in bones of the two patients with MAS. Bone biopsy specimen revealed the increased osteoclast in number. In both patients, a GSalpha mutation (Arg201 -> His) was identified in the cultured fibrous cells. Intracellular cAMP content and IL-6 secretion by the patient cells were increased. Rp-8Br-cAMP significantly inhibited IL-6 production in the patient cells, while it had no effect on normal control. The addition of dibutyryl cAMP significantly increased the synthesis of IL-6 in normal control cells. In contrast, no effect of dibutyryl cAMP on IL-6 synthesis was observed in the cells from one of the MAS patients. These data suggest that IL-6 is, at least, one of the downstream effectors of cAMP and that the increased IL-6 synthesis has a pathogenic role in the bone lesions of MAS patients via increasing the number of osteoclasts. These results may provide a new strategy for the therapy of MAS patients.

Mutations, malformations and mortality

Although DNA replication is a very accurate process, a small number of new mutations are generated at every cell division. The generation of a new mutation during the formation of an ovum or sperm cell can cause an early miscarriage or birth defect. The generation of new mutations during embryogenesis can cause a variety of localized birth defects. The molecular delineation of these errors in somatic and gonadal cells has clarified the basis of some birth defects, and has both refined and complicated genetic counselling for a number of paediatric conditions. The processes responsible for these new mutations are present in all cells. For this reason new mutations accumulate in all cells throughout life and contribute to the ageing process. Thus the molecular events that cause many miscarriages and birth defects are the same as those that ultimately lead to death.

Expanding horizons for receptors coupled to G proteins: diversity and disease

The known repertoire of seven transmembrane domain receptors coupled to G proteins has expanded in several interesting directions. Both loss-of-function and activating mutations have been found at the root of a variety of diseases. More will undoubtedly be uncovered. The diversity of ligands which trigger G protein coupled receptors continues to grow, and with it the variety of known strategies for ligand detection. These and other developments promise continued excitement in this field.

G protein mutations in human disease

The heterotrimeric G proteins couple cell-surface receptors for extracellular signals to intracellular effectors that generate second messengers. Abnormal G protein signalling, resulting from posttranslational modifications by bacterial toxins, altered gene expression, or gene mutations, may lead to diverse biological consequences. Mutations within G protein alpha subunit genes that lead to either constitutive activation or loss of function have been identified. Such G protein mutations play a role in the pathogenesis of several human diseases, including sporadic endocrine tumors, McCune-Albright syndrome, and Albright hereditary osteodystrophy.