Demonstration of McCune-Albright mutations in the liver of children with high gammaGT progressive cholestasis

Two patients presented with neonatal cholestasis and acholic stools as first manifestations of McCune-Albright syndrome. Both went through an extensive evaluation including an exploratory laparotomy with peroperative cholangiography which ruled out biliary atresia. One patient presented from the fourth month of life with the classical café-au-lait spots following Blaschko's lines, while less classical café-au-lait spots were seen in the second patient at the age of 4 years. Bone lesions were seen in one patient at the age of 2.5 years and in the other at the age of 4 years. Despite the severity of presentation, both patients cleared their jaundice within 6 months, but still had mild abnormalities of liver function tests. Both patients showed an activating mutation of codon 201 in the gene encoding the alpha-subunit of the G-protein that stimulates adenylcyclase in liver tissue, suggesting that this metabolic defect could be responsible for the cholestatic syndrome. Similar mutations have been found in other affected tissues in patients with the McCune-Albright syndrome. We propose that McCune-Albright syndrome be included in the list for differential diagnosis of neonatal cholestasis and chronic cholestasis of infancy, as a rare cause.

Resistance to the lipolytic action of epinephrine: a new feature of protein Gs deficiency

Deficiency of protein Gs (Gs; OMIM no.103580), the stimulatory regulator of adenylyl cyclase, is associated with resistance to PTH and other hormones, sc calcifications, short stature, and skeletal defects (Albright's hereditary osteodystrophy). It is caused by heterozygous loss of function mutations in GNAS 1, the gene encoding the alpha-subunit of Gs. Obesity is a classical feature of patients with Gs deficiency, but the mechanism leading to fat accumulation has not been elucidated. We measured glycerol flux, using a nonradioactive tracer dilution approach, to analyze the lipolytic response to epinephrine in 6 patients with Gs deficiency and PTH resistance and compared it to six age-matched normal controls and nine massively obese children. Basal glycerol production was reduced by 50%, and lipolytic response to epinephrine was reduced by 67%, in Gs-deficient children, as compared with controls. The degree of impairment of lipolysis was similar in Gs-deficient children who were only moderately overweight and in morbidly obese children. These findings extend the spectrum of hormonal resistance in Gs deficiency. Besides beta-adrenergic receptors, Gs protein itself should be examined as a possible step involved in the decreased lipolysis observed in common obesity.

Clinical implications of genetic defects in G proteins: oncogenic mutations in G alpha s as the molecular basis for the McCune-Albright syndrome

Signal-transducing guanine nucleotide-binding proteins (G proteins) couple extracellular receptor proteins to intracellular effector enzymes and ion channels, and therefore are critical mediators of cellular responses to external stimuli. G proteins are comprised of three subunits (alpha, beta, gamma), each encoded by many different genes. The multiplicity of G protein subunits facilitates great combinatorial variability, which, in part, accounts for the ability of G proteins to interact with many different receptor and effector proteins. Hundreds of G protein-coupled receptors have been identified, and their unique patterns of expression among a restricted number of cell types contributes greatly to the apparent specificity of hormone action. Mutations that either activate or inactivate some of these receptors account for a number of highly specific syndromes, which affect a limited number of target tissues. By contrast, most G proteins are widely expressed in many tissues. Accordingly, mutations in these signaling molecules would be expected to produce a more generalized pattern of hormone dysfunction. Activating mutations in the gene (GNAS1) that encode the alpha subunit of the G protein that stimulates adenylyl cyclase (AC) have been identified in many endocrine neoplasms and diverse tissues of patients with McCune-Albright syndrome. The McCune-Albright syndrome is characterized by autonomous endocrine function, hyperpigmented skin lesions, and fibrous dysplasia of bone--effects which reflect the ability of CAMP to stimulate cell function and proliferation in a wide variety of tissues. The unusual features of the McCune-Albright syndrome are explained by the mosaic distribution of cells bearing the mutant allele, an observation that is most consistent with postzygotic mutation of GNAS1. Experimental analysis of this syndrome has extended our understanding of the clinical and biochemical consequences of dysfunctional G protein action and has provided a bench-to-bedside demonstration of the critical role that G proteins play in transmembrane signal transduction in humans.

Etiology of fibrous dysplasia and McCune-Albright syndrome

In this paper, the etiology of monostotic fibrous dysplasia and McCune-Albright syndrome is explained. Both monostotic fibrous dysplasia and McCune-Albright syndrome are sporadically occurring disorders in which a mutation in the GNAS1 gene occurs postzygotically in a somatic cell. All cells descended from the mutated cell can manifest features of McCune-Albright syndrome or fibrous dysplasia. Cells descended from non-mutated cells develop into normal tissues. Thus, the clinical pattern is variable in distribution and appearance. More generalized vs more localized expression depend on (a) how small or how large the cell mass is during embryogenesis when the mutation occurs and (b) where in the cell mass the mutation occurs. Topics discussed include G proteins and their receptors, cycling of stimulatory G protein between active and inactive forms, and specific mutations in GNAS1. We also discuss four possibilities: (a) Are there masked mutations? (b) Are there effects of imprinting? (c) Are there non-classical mutations? and (d) Is fibrous dysplasia a neoplasm?

Identification of two novel deletion mutations within the Gs alpha gene (GNAS1) in Albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) is a genetic disorder characterized by short stature, skeletal defects, and obesity. Within AHO kindreds, some affected family members have only the somatic features of AHO [pseudopseudohypoparathyroidism (PPHP)], whereas others have these features in association with resistance to multiple hormones that stimulate adenylyl cyclase within their target tissues [pseudohypoparathyroidism type Ia (PHP Ia)]. Affected members of most AHO kindreds (both those with PPHP and those with PHP Ia) have a partial deficiency of Gs alpha, the alpha-subunit of the G protein that couples receptors to adenylyl cyclase stimulation, and in a number of cases heterozygous loss of function mutations within the Gs alpha gene (GNAS1) have been identified. Using PCR with the attachment of a high melting domain (GC-clamp) and temperature gradient gel electrophoresis, two novel heterozygous frameshift mutations within GNAS1 were found in two AHO kindreds. In one kindred all affected members (both PHP Ia and PPHP) had a heterozygous 2-bp deletion in exon 8, whereas in the second kindred a heterozygous 2-bp deletion in exon 4 was identified in all affected members examined. In both cases the frameshift encoded a premature termination codon several codons downstream of the deletion. In the latter kindred affected members were previously shown to have decreased levels of GNAS1 messenger ribonucleic acid expression. These results further underscore the genetic heterogeneity of AHO and provides further evidence that PHP Ia and PPHP are two clinical presentations of a common genetic defect. Serial measurements of thyroid function in members of kindred 1 indicate that TSH resistance progresses with age and becomes more evident after the first year of life.

Familial cryptic translocation between chromosomes 2qter and 8qter: further delineation of the Albright hereditary osteodystrophy-like phenotype

Recently five patients with an Albright hereditary osteodystrophy (AHO)-like phenotype were reported to have a subtelomeric deletion of the long arm of chromosome 2. These patients showed a striking resemblance to a number of patients from a large pedigree known to us for a long time. After molecular confirmation of a subtelomeric deletion in one patient, FISH analysis was used and a cryptic translocation between the long arms of chromosomes 2 and 8, t(2;8)(q37.3;q24.3), was detected. Remarkably, five proven and 10 probable cases with a 2qter deletion were found in the family, but none with an 8qter deletion. This was not explained by increased fetal loss. The major clinical characteristics of terminal 2q deletion are a short, stocky build, round face, sparse hair, deeply set eyes, bulbous nose, thin vermilion border, brachymetaphalangism, seizures, and developmental delay. A specific behavioural phenotype consisting of periods of hyperkinesia and aggression can develop with age. The overall phenotype is sufficiently characteristic to allow clinical recognition. The cytogenetic and molecular studies did not narrow down the common deleted region. Both testing of additional 2q markers and characterisation of other AHO-like patients with 2q37 microdeletions may help to define the candidate gene region.

[A new case of craniofacial fibrous dysplasia and cytogenetic study]

Fibrous dysplasia is an uncommon condition, which most obvious expression is the disorder of the osseous tissue setting up. Craniofacial bones are preferential sitting targets. We report a new case, in a 14-year-old boy, whose cytogenetic study neither in peripheral blood nor in tumor cells showed significantly differences.

Illustrative disorders of ectopic skeletal morphogenesis: a childhood parallax for studies in gravitational and space biology

Heterotopic ossification is a key feature of at least three distinct genetic disorders of osteogenesis in humans: fibrodysplasia ossificans progressiva, progressive osseous heteroplasia, and Albright's hereditary osteodystrophy. All three conditions are genetic disorders of childhood, but the pathobiology of osteogenic induction, the histopathology of osteogenesis, the anatomic distribution of heterotopic lesions, and the developmental patterns of disease progression differ among the three conditions. The phenotypic distinction of these disorders is critically important in counselling patients and families as well as in advancing research to define the molecular pathophysiology of heterotopic osteogenesis in these disabling genetic disorders. Genetic disorders of tissue modeling and morphogenesis provide an important parallax to disturbances of tissue re-modeling that are of paramount importance to gravitational and space biologists as humans begin to explore and live in environments beyond the planet on which they evolved. Disorders of osteogenesis are of particular concern to space biologists due to the dramatic changes in skeletal biology in altered gravitational fields.

A mutation in the heterotrimeric stimulatory guanine nucleotide binding protein alpha-subunit with impaired receptor-mediated activation because of elevated GTPase activity

It has been reported that substitution of Arg258, a residue within the GTPase domain of the heterotrimeric guanine nucleotide binding protein (G protein) alpha-subunit (alphas), to alanine (alphas-R258A) results in decreased activation by receptor or aluminum fluoride (AlF4-) and increased basal GDP release. Arg258 interacts with Gln170 in the helical domain, and, presumably, loss of this interaction between the GTPase and helical domain leads to more rapid GDP release, resulting in decreased activation by AlF4- and increased thermolability. In this study, we mutate Gln170 to alanine (alphas-Q170A) and demonstrate that this mutant, like alphas-R258A, has decreased activation by AlF4-, increased thermolability (both reversed in the presence of excess guanine nucleotide), and an increased rate of GDP release. However, unlike alphas-R258A, alphas-Q170A does not have impaired receptor-mediated activation. Therefore, this interdomain interaction is critical to maintain normal guanine nucleotide binding (and hence normal activation by AlF4-) but is not important for receptor-mediated activation. In single turnover GTPase assays, the catalytic rate for GTP hydrolysis of alphas-R258A was 14-fold higher than normal whereas that of alphas-Q170A was unaffected. Examination of the alphas crystal structure suggests that Arg258, through interactions with Glu50, might constrain the position of Arg201, a residue critical for catalyzing the GTPase reaction. This is an example of a mutation in a heterotrimeric G protein that results in an increased intrinsic GTPase activity and provides another mechanism by which G protein mutations can impair signal transduction.

A cluster of oppositely imprinted transcripts at the Gnas locus in the distal imprinting region of mouse chromosome 2

Imprinted genes tend to occur in clusters. We have identified a cluster in distal mouse chromosome (Chr) 2, known from early genetic studies to contain both maternally and paternally imprinted, but unspecified, genes. Subsequently, one was identified as Gnas, which encodes a G protein alpha subunit, and there is clinical and biochemical evidence that the human homologue GNAS1, mutated in patients with Albright hereditary osteodystrophy, is also imprinted. We have used representational difference analysis, based on parent-of-origin methylation differences, to isolate candidate imprinted genes in distal Chr 2 and found two oppositely imprinted genes, Gnasxl and Nesp. Gnasxl determines a variant G protein alpha subunit associated with the trans-Golgi network and Nesp encodes a secreted protein of neuroendocrine tissues. Gnasxl is maternally methylated in genomic DNA and encodes a paternal-specific transcript, whereas Nesp is paternally methylated with maternal-specific expression. Their reciprocal imprinting may offer insight into the distal Chr 2 imprinting phenotypes. Remarkably, Gnasxl, Nesp, and Gnas are all part of the same transcription unit; transcripts for Gnasxl and Nesp are alternatively spliced onto exon 2 of Gnas. This demonstrates an imprinting mechanism in which two oppositely imprinted genes share the same downstream exons.

McCune-Albright syndrome: clinical and molecular evidence of mosaicism in an unusual giant patient

Molecular genetics recently uncovered the mystery of the protean picture of McCune-Albright syndrome by identification of the somatic gain of function mutations in the GNAS1 gene. Here we present an adult patient with fibrous dysplasia and an endocrinopathy resulting in unusual giant height. The clinical diagnosis in the patient could be confirmed by molecular investigations in tissues involved in the process of fibrous dysplasia.

The histopathology of fibrous dysplasia of bone in patients with activating mutations of the Gs alpha gene: site-specific patterns and recurrent histological hallmarks

Gs alpha mutations and histopathology have been analysed in a series of 13 patients with fibrous dysplasia (FD) of bone, including 12 patients with the McCune-Albright syndrome (MAS) and one patient with monostotic FD. Activating mutations (either R201C or R201H) of the gene encoding the alpha subunit of the stimulatory G protein, Gs, were detected in all cases, including the case of monostotic FD, using a variety of techniques [reverse transcription-polymerase chain reaction (RT-PCR) with allele-specific primers, allele-specific oligonucleotide hybridization, and DNA sequencing]. A spectrum of bone lesions associated with such mutations was identified and it was possible to recognize three primary, but distinct, histological patterns, defined here as Chinese writing type, sclerotic/Pagetoid type, and sclerotic/hypercellular type, which are characteristically associated with the axial/appendicular skeleton, cranial bones, or gnathic bones, respectively. Features of FD histopathology were characterized by confocal fluorescence microscopy, which allowed the definition of osteogenic cell shape changes and 'Sharpey fibre bone' as common denominators of all histological subtypes. Defining characteristics of the different subtypes, two of which diverge from standard descriptions of FD and have never been characterized before, were dependent on the amount and structure of bone tissue within the FD lesion. These data emphasize the non-random (site-specific) variability of FD histopathology in patients carrying activating mutations of the Gs alpha gene and provide additional evidence for the occurrence of Gs alpha mutations in cases of FD other than typical MAS.

A novel mutation in the switch 3 region of Gsalpha in a patient with Albright hereditary osteodystrophy impairs GDP binding and receptor activation

Albright hereditary osteodystrophy (AHO), a disorder characterized by skeletal abnormalities and obesity, is associated with heterozygous inactivating mutations in the gene for Gsalpha. A novel Gsalpha mutation encoding the substitution of tryptophan for a nonconserved arginine within the switch 3 region (Gsalpha R258W) was identified in an AHO patient. Although reverse transcription-polymerase chain reaction studies demonstrated that mRNA expression from wild type and mutant alleles was similar, Gsalpha expression in erythrocyte membranes from the affected patient was reduced by 50%. A Gsalpha R258W cDNA, as well as one with arginine replaced by alanine (Gsalpha R258A), was generated, and the biochemical properties of in vitro transcription/translation products were examined. When reconstituted with cyc- membranes, both mutant proteins were able to stimulate adenylyl cyclase normally in the presence of guanosine- 5'-O-(3-thiotriphosphate) (GTPgammaS) but had decreased ability in the presence of isoproterenol or AlF4- (a mixture of 10 microM AlCl3 and 10 mM NaF). The ability of each mutant to bind and be activated by GTPgammaS or AlF4- was assessed by trypsin protection assays. Both mutants were protected normally by GTPgammaS but showed reduced protection in the presence of AlF4-. The addition of excess GDP (2 mM) was able to rescue the ability of AlF4- to protect the mutants, suggesting that they might have reduced affinity for GDP. A Gsalpha R258A mutant purified from Escherichia coli had decreased affinity for GDP and an apparent rate of GDP release that was 10-fold greater than that of wild type Gsalpha. Sucrose density gradient analysis demonstrated that both Gsalpha R258W and Gsalpha R258A were thermolabile at higher temperatures and that denaturation of both mutants was prevented by the presence of 0.1 mM GTPgammaS or 2 mM GDP. The crystal structure of Gsalpha demonstrates that Arg258 interacts with a conserved residue in the helical domain (Gln170). Arg258 substitutions would be predicted to open the cleft between the GTPase and helical domains, allowing for increased GDP release in the inactive state, resulting in enhanced thermolability and reduced AlF4--induced adenylyl cyclase stimulation and trypsin protection, since activation by AlF4- requires bound GDP.

Increased interleukin-6 production in mouse osteoblastic MC3T3-E1 cells expressing activating mutant of the stimulatory G protein

The McCune-Albright syndrome (MAS) is characterized by polyostotic fibrous dysplasia, café-au-lait spots, and multiple endocrine hyperfunction. An activating missense mutation of the alpha subunit of the Gs protein (Gs alpha) was found in several affected tissues, resulting in prolonged stimulation of adenylate cyclase. Our recent study has indicated that the cells derived from the fibrous bone dysplasia tissues in MAS patients produced increased levels of interleukin-6 (IL-6), which may be responsible for the increased bone resorption in this disease. In the present investigation, to analyze the molecular mechanism of the increased IL-6 production by activating mutant Gs alpha in bone cells, we established mouse osteoblastic MC3T3-E1 cells stably transfected with the activating mutant Gs alpha expression vector. These cells showed a significant increase of intracellular cAMP levels and produced a higher amount of IL-6 than the cells transfected with control vector or wild-type Gs alpha expression vector. Analysis of the IL-6 promoter revealed that any of the AP-1, nuclear factor (NF)-IL-6, and NF-kappa B binding elements are important for the activating mutant Gs alpha-induced gene expression. Electrophoretic mobility-shift assays using nuclear extracts of the mutant Gs alpha-expressing cells showed that phospho(Ser133)-cAMP-responsive element binding protein (CREB), AP-1, NF-IL6, and NF-kappa B were increased, compared with the control cells or the wild-type Gs alpha-expressing cells. These results indicate that activating mutant Gs alpha increases the transcriptional factors binding to CRE, AP-1, NF-IL6, and NF-kappa B elements to induce IL-6 gene expression in the osteoblastic cells.

The "Taiwanese giant": hormonal and genetic influences in fibrous dysplasia

A 14-year-old boy has been followed for 4 years with a rapidly growing, recurrent area of fibrous dysplasia of the left maxilla and zygoma following resection and bone grafting. Standing 190 cm tall, he was found to have elevated serum growth hormone levels and a pituitary adenoma. His case appears to represent a postzygotic gene mutation of McCune-Albright syndrome. It is possible that the elevated growth hormone levels are in part responsible for the rapid progression of the tumor.

Pseudohypoparathyroidism type Ia from maternal but not paternal transmission of a Gsalpha gene mutation

While loss-of-function mutations in Gsalpha are invariably associated with the short stature and brachydactyly of Albright hereditary osteodystrophy (AHO), the association with hormone resistance (to parathyroid hormone and thyrotropin) typical of pseudohypoparathyroidism type Ia (PHP-Ia) is much more variable. Observational studies and DNA polymorphism analysis suggest that maternal transmission of the Gsalpha mutation may be required for full expression of clinical hormone resistance. To test this hypothesis, we studied transmission of a frameshift mutation in Gsalpha through three generations of a pedigree affected by AHO and PHP-Ia. While all family members carrying this loss-of-function mutation in one Gsalpha allele had AHO, neither the presence of the mutation nor the degree of reduction of erythrocyte Gsalpha bioactivity allowed prediction of phenotype (AHO alone versus AHO and PHP-Ia). Paternal transmission of the mutation (from the patriarch of the first generation to three members of the second generation) was not associated with concurrent PHP-Ia, but maternal transmission (from two women in the second generation to four children in the third generation) was invariably associated with PHP-Ia. No expansion of an upstream short CCG nucleotide repeat region was detected, nor was there evidence of uniparental disomy by polymorphism analysis. This report, the first to document the effects across three generations of both paternal and maternal transmission of a specific Gsalpha mutation, strongly supports the hypothesis that a maternal factor determines full expression of Gsalpha dysfunction as PHP-Ia.

A case of Albright's hereditary osteodystrophy-like syndrome complicated by several endocrinopathies: normal Gs alpha gene and chromosome 2q37

We report a sporadic case of Albright's hereditary osteodystrophy (AHO)-like syndrome with several endocrinopathies. A 37-yr-old woman had an appearance of AHO but did not have renal PTH resistance. Her case was complicated by non-insulin-dependent diabetes mellitus with severe insulin resistance, central diabetes insipidus, and hyposecretion of GH. Most patients with AHO are found in a family of pseudohypoparathyroidism type-Ia and have a heterozygous mutation that inactivates the alpha-subunit of Gs (Gs alpha), the stimulatory regulator of adenylyl cyclase. Some sporadic cases occur in which patients with phenotype similar to AHO have a deletion of chromosome 2q37. However, in this patient, both the Gs alpha gene structure and the biological activity were normal. In addition, chromosome analysis revealed a normal pattern with no visible deletion of chromosome 2q37. Our findings suggest that one or more other factors may be involved in the pathogenesis of AHO-related disease.

Pseudohypoparathyroidism-Albright hereditary osteodystrophy

A 13 year old girl with short stature, and retarded mental growth with coarse facies and deranged thyroid function test was initially suspected as a case of hypothyroidism and was started on thyroxine. Lack of response to treatment and on further investigations it was diagnosed as a case of pseudohypoparathyroidism. High index of suspicion and careful evaluation is important to diagnose such an entity.

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.

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.

[A case of facial fibrous dysplasia in brothers]

Fibrous dysplasia is a benign bone tumor. The cranio-facial localization concern 20% of fibrous dysplasia. A congenital etiology is evoked by all the authors. Our observations ask for the real etiology of this affection: Congenital? Familial? The diagnosis is done by anatomo-pathology, and surgery is the treatment for severe cases. Relapses are frequent.

Mutations in exon 7 of the GTP-binding protein Gs alpha were not a common cause of pseudohypoparathyroidism with Albright's hereditary osteodystrophy in Japanese

The identification of unique point mutations in patients with pseudohypoparathyroidism (PHP) with Albright's hereditary osteodystrophy (AHO) in different ethnic backgrounds has proved that defects within the Gs alpha gene account for Gs alpha deficiency in those patients. To search a mutation hot spot of the Gs alpha gene in Japanese patients, we have screened exons 2-13 of the Gs alpha gene for mutations in three unrelated Japanese PHP patients with AHO. We could find no abnormalities by denaturing gradient gel electrophoresis and no mutations of sequencing of exon 7 in these subjects. This suggests that mutations in exon 7 of the Gs alpha gene may not be a common cause of PHP with AHO in Japanese.

Disorders of puberty: inactivating and activating molecular mutations

Recent developments have increased our understanding of the molecular mechanisms that are responsible for several disorders of puberty. Specific gene mutations have been identified in three syndromes, one that is associated with delayed puberty (Kallmann syndrome) and two that are associated with precocious puberty (McCune-Albright syndrome and familial male precocious puberty). Mutations in the KAL gene have been shown to be responsible for cases of X-linked Kallmann syndrome. This gene encodes a protein that is believed to be involved in neural target recognition and protease inhibition. In McCune-Albright syndrome, heterozygous, postzygotic somatic mutations of the alpha-subunit of the stimulatory guanine nucleotide binding protein Gs have been shown to stimulate constitutive G protein activation and long-term cyclic adenosine monophosphate production. Similarly, familial male precocious puberty has been linked to gain-in-function mutations that result in increased levels of cyclic adenosine monophosphate; however, these mutations are found in the luteinizing hormone receptor gene itself. The clinical manifestations and the recent molecular advances in each of these three syndromes are explored.

Hyperthyroidism in McCune-Albright syndrome with a review of thyroid abnormalities sixty years after the first report

We present a patient with hyperthyroidism associated with McCune-Albright syndrome (MAS). MAS is a sporadic genetic disease characterized by polyostotic fibrous dysplasia, cafe au lait cutaneous spots and endocrinopathies (peripheral precocious puberty, thyroidopathies, acromegaly, etc.). It is caused by an activating mutation of the gene for the Gs alpha membrane-associated protein, which mediates the thyrotropin (TSH)-induced and other hormone-induced activation of adenylyl cyclase. A 13-month-old girl was diagnosed with MAS. Precocious puberty was treated initially with testolactone and later with oophorectomy. Subclinical hyperthyroidism was detected biochemically at birth, and 10 months later, it became clinically evident, albeit mild, with absence of goiter. A concomitant liver dysfunction precluded treatment with thionamides and she was sporadically treated with beta-blockers. The combination of increased free thyroxine (T4) and triiodothyronine (T3) with low plasma thyrotropin (TSH) levels in the absence of thyroid-stimulating autoantibodies persisted until the age of 6 years, when she was referred to our unit. Hyperthyroidism was then clinically evident with cardiac hyperactivity, and it was cured with administration of radioiodine (131I). Thyroid disease is the second most common endocrinopathy associated with MAS, and since 1936, 63 cases of thyroidopathies have been described, including 19 nodular (14 with and 5 without hyperthyroidism) and 23 diffuse (20 with and 3 without hyperthyroidism) goiters, and 18 cases of hyperthyroidism without goiter. The previously described somatic activating mutation of the gs alpha gene in the ovaries, the liver and the peripheral blood of our patient, in the absence of stigmata, autoimmunity might be incriminated for the secretory and mitotic activation of the thyroid gland. We suggest the treatment of choice of hyperthyroidism in MAS patients should be 131I administration because: (a) hyperthyroidism is very likely to recur after withdrawal of antithyroid medication; (b) the morbidity of these patients is elevated; (c) oophorectomized patients do not need to be advised to avoid procreation during the months after 131I administration; and (d) finally, even in the usual cases of hyperthyroidism in childhood, 131I treatment is becoming more popular worldwide.

RDCI, the vasoactive intestinal peptide receptor: a candidate gene for the features of Albright hereditary osteodystrophy associated with deletion of 2q37

Albright hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterised by the presence of brachymetaphalangism, short stature, obesity, and mental retardation. Variable biochemical changes many represent either pseudohypoparathyroidism (PHP) owing to resistance to parathormone (PTH) or pseudopseudohypoparathyroidism (PPHP) with no hormone resistance. In most cases of AHO, reduced levels of Gs alpha have been found and a number of deactivating mutations in the gene for Gs alpha located on chromosome 20q13 have been described. Recently a number of people with an AHO-like phenotype have been reported in whom a deletion of chromosomal region 2q37 has been found in the absence of biochemical abnormalities or a reduction in Gs alpha activity. We present a further female patient with a cytogenetically visible deletion of 2q37, an AHO-like phenotype, and unusual biochemistry suggesting moderate PTH resistance. The vasoactive intestinal peptide receptor (RDCI) has recently been mapped to 2q37 and we propose that this is a candidate gene, hemizygosity of which affects signal transduction and leads to the AHO-like phenotype found in patients with 2q37 deletions.

Increased proliferation of osteoblastic cells expressing the activating Gs alpha mutation in monostotic and polyostotic fibrous dysplasia

We studied the osteoblastic abnormalities resulting from activating mutation of the Gs alpha gene in two patients with McCune-Albright syndrome and one patient with monostotic fibrous dysplasia. Histomorphometric analysis of dysplastic lesions showed a low number of differentiated osteoblasts along the bone surface and numerous immature alkaline phosphatase-positive mesenchymal cells actively depositing a woven bone matrix. Osteoblastic cells isolated from dysplastic bone lesions expressed a missense mutation in the Gs alpha gene in position 201 and showed increased intracellular basal cyclic adenosine 3',5'-monophosphate levels compared with normal cells isolated from a noninvolved area in the same patient. Cell proliferation evaluated by DNA synthesis was two-fold to threefold greater in osteoblastic cells expressing the mutation compared with normal cells from the same patient and was greater in cells isolated from more severe than less severe fibrotic lesions. In contrast, the synthesis of osteocalcin, a marker of mature osteoblasts, was lower in osteoblastic cells expressing the Gs alpha mutation compared with normal cells from the same patient and was lower in cells isolated from severe compared with less severe fibrotic lesions, indicating that the increased growth in mutated osteoblastic cells was associated with reduced cell differentiation. The results show that activating mutation of Gs alpha in osteoblastic cells leads to constitutive activation of adenylate cyclase, increased cell proliferation, and inappropriate cell differentiation, resulting in overproduction of a disorganized fibrotic bone matrix in polyostotic and monostotic fibrous dysplasia.

The molecular basis of disorders caused by defects in G proteins

G proteins couple receptors for many hormones to effectors that regulate second messenger metabolism. G protein dysfunction could involve gain or loss of function. For Gs, the G protein that couples receptors to stimulation of cAMP formation, examples of both types have already been defined. Germline loss of function mutations in the Gs(alpha) gene are responsible for a form of inherited hormone resistance termed pseudohypoparathyroidism (Albright hereditary osteodystrophy). Conversely, somatic gain of function mutations cause constitutive stimulation of cAMP, independent of receptor activation, in acromegaly, in hyperfunctional thyroid nodules, and in the McCune-Albright syndrome. Future work is likely to uncover additional disorders caused by defective G proteins with implications for diagnosis and treatment.

[Primary cutaneous osteoma in hereditary Albright osteodystrophy]

Cutaneous osteomas occur rarely; they represent the formation of bone in the skin. Primary and secondary forms of ossification can be distinguished. We describe the primary form of ossification in a child with Albright's hereditary osteodystrophy.

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.

Familial Albright's hereditary osteodystrophy with hypoparathyroidism: normal structural Gs alpha gene

Albright's hereditary osteodystrophy (AHO) is a characteristic skeletal phenotype, including short stature, obesity, round face, and brachydactyly. AHO appears in patients with pseudohypoparathyroidism (PHP) who have resistance to PTH and in their eumetabolic family members who have pseudopseudohypoparathyroidism (PPHP). The differential diagnosis of AHO in families without PHP includes brachydactyly E, whose existence as a distinct entity has been questioned. We studied a patient with familial AHO who presented with hypocalcemia. To our surprise, PTH levels were low, and the response to PTH administration was normal. This is the first case of familial AHO with hypoparathyroidism. The proband's family included 22 affected subjects spanning 3 generations, who had variable degrees of AHO manifestations, with an autosomal dominant inheritance trait. The metacarpophalangeal pattern profile was typical of that of PHP-PPHP. As deficient activity and inactivating mutations of Gs alpha were described in PHP as well as in PPHP, we measured the biological activity of Gs in family members, which was normal. To exclude subtle abnormalities in the Gs alpha gene, we sequenced the entire coding region of Gs alpha in the propositus, which was normal. We conclude that hypocalcemia should be adequately evaluated even in the presence of familial AHO, and that familial AHO can occur with a normal coding structural Gs alpha gene. Identification of the molecular defect in familial AHO without PHP will shed light on the pathogenesis of AHO in general.

Gonadotrophin receptors

Precocious puberty may be gonadotrophin-dependent, due to premature activation of the hypothalamic GnRH pulse generator, or gonadotrophin-independent wherein serum LH and FSH levels are undetectable despite near-adult levels of gonadal steroidogenesis. In one form of gonadotrophin-independent familial male precocious puberty (FMPP) activating mutations of the LH receptor cause constitutive activation of the cAMP signal transduction cascade in Leydig cells with attendant testosterone biosynthesis. The LH receptor is a member of the seven transmembrane group of receptors coupled to signal transduction through GTP binding intermediate proteins. In FMPP the initial mutations were described in the sixth membrane spanning domain close to the third intracellular loop which is known to be important for coupling to the subunit of the stimulatory GTP binding protein Gs. Subsequently, activating mutations at several other sites in the LH receptor have been described. Activating mutations in the second step of the signalling cascade, the GTP binding protein Gs, have been described in sporadic somatotrophinomas in the pituitary and solitary thyroid adenomas. The McCune-Albright syndrome may also be rarely associated with pituitary and thyroid adenomas, in addition to the more common polyostotic fibrosus dysplasia and gonadotrophin-independent precocious puberty. Thus, in the luteinized ovarian tissue of patients with this condition activating mutations in Gs alpha subunit have been described at codon 201. These mutations are somatic, not germ line, and only one allele needs to be affected as they are dominant. In an uncommon form of male pseudohermaphroditism associated with hypergonadotrophic hypogonadism and Leydig cell hypoplasia, inactivating mutations of the LH receptor are described. These, too, are in the sixth transmembrane domain and both alleles must be mutant as the condition is autosomal recessive. These 'experiments of nature' have provided invaluable insights into the structure-function relations of the LH receptor, and the mutations described have been recreated and studied in vitro, where the predicted activation or failure to stimulate steroidogenesis confirm their pathogenic nature. As yet no such activating or inhibiting mutations in the FSH receptor gene have been described, but it is likely these will be forthcoming in future.

Endocrine disorders associated with mutations in guanine nucleotide binding proteins

The basis for a number of relatively rare endocrine diseases, which present clinically with features of AHO, have been shown conclusively to result from mutations in the G3 alpha gene which interfere with the expression of functional protein. Individual kindreds display a range of specific mutations in this gene. A further series of disorders result from somatic mutations of the G3 alpha gene which result in constitutive activation (in one case probably with a concomitant decrease in stability of the expressed protein). When such a mutation occurs in early embryogenesis it can result in a pattern of mosaicism of expression of clinical features in the patient. Despite these cases, equivalent alterations in other G-protein alpha subunit genes seem to be of limited importance in human disease. This is despite biochemical data from a range of experimental cell models which indicate that such mutations can have potent effects on cell growth and division.

[Mutation of G proteins]

Guanine nucleotide-binding proteins (G proteins) function as transducers of information across the cell membrane by coupling receptors to effectors. A large number of G protein-linked receptors funnel extracellular signals as diverse as hormones, growth factors, neurotransmitters, and primary sensory stimuli through a set of G proteins to a small number of second-messenger systems. The G proteins act as molecular switches with an "on" and "off" state governed by a GTPase cycle. By virtue of its high affinity and specificity for guanine nucleotide binding and its intrinsic GTPase activity, the alpha-subunit of the G protein (G alpha) plays the critical role in regulation of the effectors by their corresponding G protein. Mutations of G alpha may result in either constitutive activation or loss of expression mutations. Given the variety of functions subserved by G protein-coupled signal transduction, it is not surprising that abnormalities in G protein-coupled pathways can lead to diseases with manifestations as dissimilar as blindness, hormone resistance, precocious puberty and neoplasia. For a given defect in a G protein-coupled pathway, the extent of the manifestations will also be determined by the cellular distribution of the affected component. Defects in components expressed exclusively in a single cell type will cause more a focal disorder than defects in a widely expressed component, particularly in germline mutations (e.g., Albright's hereditary osteodystrophy), whereas somatic mutations of genes encoding even an ubiquitously expressed component can cause focal disease when the somatic mutation itself is focal (e.g., McCune-Albright syndrome).

Albright hereditary osteodystrophy and del(2) (q37.3) in four unrelated individuals

Albright hereditary osteodystrophy (AHO) is a condition with characteristic physical findings (short stature, obesity, round face, brachydactyly) but variable biochemical changes (pseudohypoparathyroidism, pseudopseudohypoparathyroidism). Most patients with AHO have decreased activity of the guanine nucleotide-binding protein (GS protein) that stimulates adenylyl cyclase. The gene encoding the alpha subunit of the GS protein (GNAS1) has been mapped to the long arm of chromosome 20. We describe 4 unrelated individuals with apparent AHO, associated with small terminal deletions of chromosome 2. All 4 patients had normal serum calcium levels consistent with pseudopseudohypoparathyroidism. Del(2) (q37) is the first consistent karyotypic abnormality that has been documented in AHO [Phelan et al., 1993: Am J Hum Genet 53:484]. The finding of the same small terminal deletion in 4 unrelated individuals with a similar phenotype suggests that a gene locus in the 2q37 region is important in the pathogenesis of Albright syndrome. The association of Albright syndrome and the GNAS1 locus on chromosome 20 is well documented. The observation of a second potential disease locus on chromosome 2 may help explain the heterogeneity observed in this disorder.

Hemifacial spasm in Albright's hereditary osteodystrophy with pseudopseudohypoparathyroidism and nephrogenic diabetes insipidus--case report

A 30-year-old male with Albright's hereditary osteodystrophy, pseudopseudohypoparathyroidism, and nephrogenic diabetes insipidus presented with hemifacial spasm persisting for 2 years. This association is extremely unusual. Angiography revealed markedly tortuous carotid and vertebral arteries inconsistent with his age. Neurovascular decompression of the left vertebral artery achieved only partial resolution of the spasm.

Mutations of signal-transducing G proteins in human disease

Heterotrimeric guanine nucleotide binding proteins (G proteins) couple a large number of cell surface receptors to their intracellular effector molecules, such as enzymes or ion channels. Mutations of G proteins can lead to either activation or inactivation of the corresponding signal transduction pathway and thus cause clinical symptoms. Mutations of heterotrimeric G proteins have been found in a number of endocrine tumors, the McCune-Albright syndrome, Albright's hereditary osteodystrophy, and a combination of precocious puberty and pseudohypoparathyroidism Ia. The identification of the molecular defects underlying the above disorders and the investigation of their functional consequences for metabolism and growth regulation have been the subject of many studies over the past few years. A close understanding of these pathophysiologic mechanisms is crucial for the development of therapeutic strategies.

Brachydactyly and mental retardation: an Albright hereditary osteodystrophy-like syndrome localized to 2q37

We report five patients with a combination of brachymetaphalangia and mental retardation, similar to that observed in Albright hereditary osteodystrophy (AHO). Four patients had cytogenetically visible de novo deletions of chromosome 2q37. The fifth patient was cytogenetically normal and had normal bioactivity of the alpha subunit of Gs (Gs alpha), the protein that is defective in AHO. In this patient, we have used a combination of highly polymorphic molecular markers and FISH to demonstrate a microdeletion at 2q37. The common region of deletion overlap involves the most telomeric 2q marker, D2S125, and extends proximally for a maximum distance of 17.6 cM. We suggest this represents a consistent phenotype associated with some deletions at 2q37 and that genes important for skeletal and neurodevelopment lie within this region. Screening for deletions at this locus should be considered in individuals with brachymetaphalangia and mental retardation. Furthermore, 2q37 represents a candidate region for type E brachydactyly.

Parental origin of Gs alpha gene mutations in Albright's hereditary osteodystrophy

Heterozygous mutations of the Gs alpha gene leading to reduced Gs alpha activity have been identified in patients with Albright's hereditary osteodystrophy (AHO). However, AHO may be associated with hormone resistance (pseudohypoparathyroidism type Ia, PHPIa) or a normal response (pseudo-pseudohypoparathyroidism, PPHP). As both disorders may occur within the same family, the relationship between Gs alpha genotype and phenotype remains unresolved. The AHO phenotype may be dependent upon the sex of the parent transmitting the Gs alpha mutation, perhaps through a gene imprinting mechanism. We have used an intragenic Gs alpha FokI polymorphism to determine the parental origin of Gs alpha gene mutations in sporadic and familial AHO. We now show that a de novo G-->A substitution at the exon 5 donor splice junction in a child with PPHP was paternally derived. Furthermore, in a female with PPHP, the Gs alpha abnormality was shown to be of paternal origin, while subsequent maternal processing and transmission resulted in PHPIa in two offspring. As transmission of PPHP has rarely been reported, determining parental origin of the disease allele in sporadic cases may provide insight into the mechanism of hormone resistance in AHO.

Albright's hereditary osteodystrophy

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