Two further AHO-like syndrome patients with deletion of glypican 1 gene region in 2q37.2-q37.3

In this report, we describe two unrelated patients with mental retardation and brachydactyly E classified as patients suffering from Albright hereditary osteodystrophy-like (AHO-like) syndrome. Fluorescence in situ hybridization (FISH) analysis using 8 different subtelomeric probes in 2q36-37 proved that the patients had subtelomeric 2qter deletions of similar size. The recently proposed candidate gene glypican 1 (GPC1) is deleted in both reported patients.

Bone morphogenetic proteins are expressed by both bone-forming and non-bone-forming lesions

CONTEXT

Bone morphogenetic proteins (BMPs) are thought to be responsible for bone formation; they cause bone to form in soft tissues and are clinically used in helping fracture union or tumor reconstructions. Skeletal metastases from epithelial tumors may be either bone-forming (blastic) or non-bone-forming (lytic).

OBJECTIVE

We studied the expression of BMPs in a variety of primary and secondary lesions of bone (both bone-forming and non-bone-forming) to determine if there was a consistent relationship between bone formation and BMP expression.

DESIGN

We compared a bone-forming lesion (fibrous dysplasia) with a non-bone-forming lesion (desmoid tumor), using reverse transcription-polymerase chain reaction, Northern blot analysis, and immunohistochemistry to detect BMPs. We also studied a number of non-bone-forming secondary lesions (carcinomas that formed lytic metastases to the skeleton) and found BMP production in most of these tumors.

RESULTS

We found that BMPs were expressed in both bone-forming and non-bone-forming benign musculoskeletal lesions. In the first part of the study, BMPs were found in both fibrous dysplasia and desmoid tumors. Bone morphogenetic proteins were also expressed by several tumors. In the next part of the study (paraffin-embedded tissue), BMPs were expressed by a variety of tumors, irrespective of the radiological nature (blastic or lytic) of their metastases.

CONCLUSIONS

We conclude that BMP production alone cannot explain bone formation, and other factors either alone or in combination may be responsible for blastic metastases to the skeleton and for bone formation by primary bone lesions, such as fibrous dysplasia.

Inherited ossifying diseases

Inherited ossifying diseases are relatively uncommon diseases leading ta a great disability and life-threatening complications. Fibrodysplasia Ossificans Progressiva is characterized by the association of skeletal abnormalities mainly in great toes, and enchondral ossifications in tendons and muscles. BMP dysregulation seems to be the main underlying mechanism of the heterotopic ossifications. The genetic basis remain controversial between a mutation on chromosome 4 or 17. Progressive Osseous Heteroplasia (HOP), more recently described, shares some similarities with Albrights hereditary osteodystrophy. In HOP, the intramembranous ossifications progressively developped from the dermis to the deeper layer. The genetic abnormality involved the GNAS 1 gene leading to an inactivation of the alpha subunit of the G protein-complex. Some therapeutic approaches have been tried: angiogenesis inhibition, mast cell inhibition; others remained in project: BMP 4 inhibition; actually there is no proved efficacy of any of them.

Parental origin of Gsalpha mutations in the McCune-Albright syndrome and in isolated endocrine tumors

Activating mutations of the Gsalpha gene are detected in different endocrine tumors, such as GH-secreting adenomas and toxic thyroid adenomas, and in hyperfunctioning glands from patients with McCune-Albright syndrome (MAS). There is increasing evidence that the Gsalpha gene is subjected to imprinting control and that Gsalpha imprinting plays a key role in the pathogenesis of different human diseases. The aim of this study was to investigate the presence of a parent specificity of Gsalpha mutations in 10 patients affected with MAS and 12 isolated tumors (10 GH-secreting adenomas, one toxic thyroid adenoma, and one hyperfunctioning adrenal adenoma). The parental origin of Gsalpha mutations was assessed by evaluating NESP55 and exon 1A transcripts, which are monoallelically expressed from the maternal and paternal alleles, respectively. By this approach, we demonstrated that in isolated GH-secreting adenomas, as well as in MAS patients with acromegaly, Gsalpha mutations were on the maternal allele. By contrast, the involvement of other endocrine organs in MAS patients was not associated with a particular parent specificity, as precocious puberty and hyperthyroidism were present in patients with mutations on either the maternal or the paternal allele. Moreover, isolated hyperfunctioning thyroid and adrenal adenomas displayed the mutation on the maternal and paternal alleles, respectively. These data confirm the importance of Gsalpha imprinting in the pituitary gland and point out the high degree of tissue specificity of this phenomenon.

Activating Gsalpha mutations: analysis of 113 patients with signs of McCune-Albright syndrome--a European Collaborative Study

McCune-Albright syndrome (MAS) is a sporadic disorder characterized by the classic triad of polyostotic fibrous dysplasia, café-au-lait skin pigmentation, and peripheral precocious puberty. It is due to postzygotic activating mutations of arginine 201 in the guanine-nucleotide-binding protein (G protein) alpha-subunit (Gsalpha), leading to a mosaic distribution of cells bearing constitutively active adenylate cyclase. MAS is heterogeneous: beyond the classic triad, a number of atypical or partial presentations have been reported. We present here the results of a systematic search for Gsalpha mutations in patients presenting with at least one of the signs of MAS, using a PCR-based sensitive method. We studied 113 patients (98 girls and 15 boys), 24% presenting the classic triad, 33% with two signs, and 40% with only one classic sign. Overall, the mutation was identified in 43% of the patients. When an affected tissue was available, the mutation was found in more than 90% of the patients, whatever the number of signs. Skin was a noteworthy exception because only three of the 11 skin samples were positive. The mutation was detected in 46% of blood samples in patients presenting the classic triad, whereas this figure fell to 21% and 8% in patients with two and one sign, respectively. Our results highlight the frequency of partial forms of MAS and the usefulness of sensitive techniques to confirm the diagnosis at the molecular level. It should be emphasized that we found the mutation in 33% of the 39 cases of isolated peripheral precocious puberty. This study has further widened the definition of MAS. Affections as clinically different as monostotic fibrous dysplasia, isolated peripheral precocious puberty, neonatal liver cholestasis, and the classic MAS all appear to be components of a wide spectrum of diseases based on the same molecular defect.

A novel technique based on a PNA hybridization probe and FRET principle for quantification of mutant genotype in fibrous dysplasia/McCune-Albright syndrome

Somatic mutations are present in various proportions in numerous developmental pathologies. Somatic activating missense mutations of the GNAS gene encoding the Gs(alpha) protein have previously been shown to be the cause of fibrous dysplasia of bone (FD)/McCune-Albright syndrome (MAS). Because in MAS patients, tissues as diverse as melanocytes, gonads and bone are affected, it is generally accepted that the GNAS mutation in this disease must have occurred early in development. Interestingly, it has been shown that the development of an active FD lesion may require both normal and mutant cells. Studies of the somatic mosaic states of FD/MAS and many other somatic diseases need an accurate method to determine the ratio of mutant to normal cells in a given tissue. A new method for quantification of the mutant:normal ratio of cells using a PNA hybridization probe-based FRET technique was developed. This novel technique, with a linear sensitivity of 2.5% mutant alleles, was used to detect the percentage mutant cells in a number of tissue and cell culture samples derived from FD/MAS lesions and could easily be adapted for the quantification of mutations in a large spectrum of diseases including cancer.

What have rare genetic syndromes taught us about the pathophysiology of the common forms of obesity?

Obesity is a central feature for several congenital syndromes, including Prader-Willi, Angelman, Bardet-Biedl, Cohen, Alström, and Börjeson-Forssman-Lehmann syndromes, and Albright's hereditary osteodystrophy. Although a role for the central nervous system, including the hypothalamus-pituitary axis, has been suggested for the etiology of obesity in these syndromes, the pathophysiologic pathways are as yet not well defined, and in many cases may identify currently unknown mechanisms. Nevertheless, many of the causative genes and unusual mechanisms, including parental imprinting of genes and complex patterns of inheritance, have been identified. We review the latest advances in understanding congenital syndromes in which obesity is purely genetic, drawing on comparisons to genetic studies of obesity in the human population as well as to those in experimental and agricultural animal models. An understanding of the genetic basis for these syndromes will provide a more comprehensive picture of the mechanisms that control food intake and energy balance in humans.

Management of infertility in a patient presenting with ovarian dysfunction and McCune-Albright syndrome

Persistent autonomous ovarian dysfunction in McCune-Albright syndrome (MAS) patients is associated with the development of multiple dominant follicles, premature luteinization, cyst formation, and anovulatory infertility. Due to the mosaic distribution of the mutation, ovaries may be unequally affected. In the current patient, the least affected ovary became quiescent upon GnRH agonist-induced gonadotropin suppression. Normoovulatory cycles were restored after subsequent removal of the affected right ovary, and a pregnancy was established within 3 months. A healthy unaffected girl was born at term after an uneventful pregnancy. The placental tissue was normal, and the mutation was not detected in the placenta, umbilical cord structures, or umbilical cord blood. GnRH analog administration may help to identify those MAS patients who might benefit from unilateral ovariectomy. Because a healthy baby was born, evidence is provided suggesting that MAS is not passed on to the children from the parents.

Thyroid carcinoma in the McCune-Albright syndrome: contributory role of activating Gs alpha mutations

McCune-Albright syndrome (MAS) is defined by the triad of café-au-lait skin pigmentation, polyostotic fibrous dysplasia, and hyperfunctioning endocrinopathies, such as precocious puberty, hyperthyroidism, GH excess, and Cushing's syndrome. This disorder is caused by sporadic, postzygotic activating mutations in the GNAS1 gene, which codes for the G(s)alpha protein in the cAMP signaling cascade. Nodular and diffuse goiters (with and without hyperthyroidism), as well as benign thyroid nodules, have been reported in association with MAS. Herein we report two cases of thyroid carcinoma in patients with MAS. The first is a case of papillary thyroid cancer detected incidentally during a hemithyroidectomy for hyperthyroidism in a 14-yr-old girl. The second is one of a 41-yr-old woman with long-standing MAS and an enlarging thyroid nodule, which was diagnosed as a clear cell thyroid carcinoma, a rare variant of thyroid cancer. Molecular analysis revealed that foci of malignancy and adjacent areas of hyperplasia and some areas of normal thyroid harbored activating mutations of Arg(201) in the GNAS1 gene. These findings suggest that the infrequent development of thyroid carcinoma in MAS patients involves additional mutational or epigenetic events.

Fgd1, the Cdc42 GEF responsible for Faciogenital Dysplasia, directly interacts with cortactin and mAbp1 to modulate cell shape

FGD1 mutations result in Faciogenital Dysplasia (FGDY), an X-linked human disease that affects skeletal formation and embryonic morphogenesis. FGD1 and Fgd1, the mouse FGD1 ortholog, encode guanine nucleotide exchange factors (GEF) that specifically activate Cdc42, a Rho GTPase that controls the organization of the actin cytoskeleton. To further understand FGD1/Fgd1 signaling and begin to elucidate the molecular pathophysiology of FGDY, we demonstrate that Fgd1 directly interacts with cortactin and mouse actin-binding protein 1 (mAbp1), actin-binding proteins that regulate actin polymerization through the Arp2/3 complex. In yeast two-hybrid studies, cortactin and mAbp1 Src homology 3 (SH3) domains interact with a single Fgd1 SH3-binding domain (SH3-BD), and biochemical studies show that the Fgd1 SH3-BD directly binds to cortactin and mAbp1 in vitro. Immunoprecipitation studies show that Fgd1 interacts with cortactin and mAbp1 in vivo and that Fgd1 SH3-BD mutations disrupt binding. Immunocytochemical studies show that Fgd1 colocalizes with cortactin and mAbp1 in lamellipodia and membrane ruffles, and that Fgd1 subcellular targeting is dynamic. By using truncated cortactin proteins, immunocytochemical studies show that the cortactin SH3 domain targets Fgd1 to the subcortical actin cytoskeleton, and that abnormal Fgd1 localization results in actin cytoskeletal abnormalities and significant changes in cell shape and viability. Thus, this study provides novel in vitro and in vivo evidence that Fgd1 specifically and directly interacts with cortactin and mAbp1, and that these interactions play an important role in regulating the actin cytoskeleton and, subsequently, cell shape.

Osteomalacic and hyperparathyroid changes in fibrous dysplasia of bone: core biopsy studies and clinical correlations

Deposition, mineralization, and resorption of FD bone compared with unaffected bone from FD patients was investigated in iliac crest biopsy specimens from 13 patients. Compared with unaffected bone, lesional FD bone seemed to be very sensitive to the effects of PTH and renal phosphate wasting, which respectively bring about hyperparathyroid or osteomalacic changes in the lesional bone.

INTRODUCTION

Fibrous dysplasia is a genetic noninherited disease caused by activating mutations of the GNAS1 gene, resulting in the deposition of qualitatively abnormal bone and marrow. This study was designed to learn more about the local processes of bone deposition, mineralization, and resorption within lesional fibrous dysplasia (FD) bone compared with unaffected bone of FD patients.

METHODS

Histology, histomorphometry, and quantitative back-scattered electron imaging (qBSE) analysis was conducted on affected and unaffected biopsy specimens from 13 patients and correlated to markers of bone metabolism.

RESULTS AND CONCLUSIONS

There was a marked excess of unmineralized osteoid with a nonlamellar structure and a reduced mineral content in mineralized bone within FD lesions (p < 0.001). A negative correlation (p = 0.05) between osteoid thickness (O.Th) and renal tubular phosphate reabsorption (measured as TmP/GFR) was observed for lesional bone, but not for unaffected bone, in which no histological or histomorphometric evidence of osteomalacia was observed in patients with renal phosphate wasting. Histological and histomorphometric evidence of increased bone resorption was variable in lesional bone and correlated with serum levels of parathyroid hormone (PTH). Hyperparathyroidism-related histological changes were observed in fibrous dysplastic bone, but not in the unaffected bone, of patients with elevated serum PTH secondary to vitamin D deficiency. Our data indicate that, compared with unaffected bone, lesional FD bone is very sensitive to the effects of PTH and renal phosphate wasting, which, respectively, bring about hyperparathyroid or osteomalacic changes in the lesional bone. Osteomalacic and hyperparathyroid changes, which emanate from distinct metabolic derangements (which superimpose on the local effects of GNAS1 mutations in bone), influence, in turn, the severity and type of skeletal morbidity in FD.

Molecular analysis of the GNAS1 gene for the correct diagnosis of Albright hereditary osteodystrophy and pseudohypoparathyroidism

Pseudohypoparathyroidism (PHP) is a heterogeneous disease characterized by PTH resistance and classified as types Ia, Ib, Ic, and II, according to its different pathogenesis and phenotype. PHP-Ia patients show Gsalpha protein deficiency, PTH resistance, and typical Albright hereditary osteodystrophy (AHO). Heterozygous mutations in the GNAS1 gene encoding the Gsalpha protein have been identified both in PHP-Ia and in pseudopseudohypoparathyroidism (PPHP), a disorder with isolated AHO. A single GNAS1 mutation may be responsible for both PHP-Ia and PPHP in the same family when inherited from the maternal and the paternal allele, respectively, suggesting that GNAS1 is an imprinted gene. To evaluate whether molecular diagnosis is a useful tool to characterize AHO and PHP when testing for Gsalpha activity and PTH resistance is not available, we have performed GNAS1 mutational analysis in 43 patients with PTH resistance and/or AHO. Sequencing of the whole coding region of the GNAS1 gene identified 11 mutations in 18 PHP patients, eight of which have not been reported previously. Inheritance was ascertained in 13 cases, all of whom had PHP-Ia: the mutated alleles were inherited from the mothers, who had AHO (PPHP), consistent with the proposed imprinting mechanism. GNAS1 molecular analysis confirmed the diagnosis of PHP-Ia and PPHP in the mutated patients. Our results stress the usefulness of this approach to obtain a complete diagnosis, expand the GNAS1 mutation spectrum, and illustrate the wide mutation heterogeneity of PHP and PHP-Ia.

A new heterozygous mutation (L338N) in the human Gsalpha (GNAS1) gene as a cause for congenital hypothyroidism in Albright's hereditary osteodystrophy

OBJECTIVE

To identify the molecular defect by which psychomotor retardation is caused in two brothers with congenital hypothyroidism who received adequate treatment with l-thyroxine.

CASE REPORT

A six-year-old boy presented with psychomotor retardation and congenital primary hypothyroidism (CH). The patient had a normal blood thyrotrophin (TSH) level on neonatal screening, but low total serum thyroxine and triiodothyronine concentrations prompting thyroid hormone substitution shortly after birth. Nevertheless, psychomotor development was retarded and the patient underwent further investigation. Typical features of Albright's hereditary osteodystrophy (AHO) such as round face, obesity, and shortened 1st, 4th and 5th metacarpals were found.

METHODS AND RESULTS

Further investigation confirmed AHO with pseudohypoparathyroidism (PHP) type Ia. The boy had a mild resistance to parathyroid hormone and a reduced adenylyl cyclase stimulating protein (Gsalpha) activity in erythrocytes. DNA analysis detected a new heterozygous mutation (L338N) in the Gsalpha protein (GNAS1) gene. This mutation was also present in the patient's brother who had similar features and was also treated with thyroid hormone because of CH, and in the phenotypically normal-looking mother who had a normal calcium metabolism but a reduced Gsalpha protein activity in erythrocytes suggestive of pseudopseudohypoparathyroidism.

CONCLUSION

In patients with CH, in whom the neurological outcome is poor even under adequate thyroid hormone substitution, PHP Ia may be suspected, especially when symptoms of AHO are present.

Analysis of GNAS1 and overlapping transcripts identifies the parental origin of mutations in patients with sporadic Albright hereditary osteodystrophy and reveals a model system in which to observe the effects of splicing mutations on translated and untranslated messenger RNA

Albright hereditary osteodystrophy (AHO) is caused by heterozygous deactivating GNAS1 mutations. There is a parent-of-origin effect. Maternally derived mutations are usually associated with resistance to parathyroid hormone termed "pseudohypoparathyroidism type Ia." Paternally derived mutations are associated with AHO but usually normal hormone responsiveness, known as "pseudo-pseudohypoparathyroidism." These observations can be explained by tissue-specific GNAS1 imprinting. Regulation of the genomic region that encompasses GNAS1 is complex. At least three upstream exons that splice to exon 2 of GNAS1 and that are imprinted have been reported. NESP55 is exclusively maternally expressed, whereas exon 1A and XL alphas are exclusively paternally expressed. We set out to identify the parental origin of GNAS1 mutations in patients with AHO by searching for their mutation in the overlapping transcripts. This information would be of value in patients with sporadic disease, for predicting their endocrine phenotype and planning follow-up. In doing so, we identified mutations that resulted in nonsense-mediated decay of the mutant Gs alpha transcript but that were detectable in NESP55 messenger RNA (mRNA), probably because they lie within its 3' untranslated region. Analysis of the NESP55 transcripts revealed the creation of a novel splice site in one patient and an unusual intronic mutation that caused retention of the intron in a further patient, neither of which could be detected by analysis of the Gs alpha complementary DNA. This cluster of overlapping transcripts represents a useful model system in which to analyze the effects that mutant sequence has on mRNA-in particular, splicing-and the mechanisms of nonsense-mediated mRNA decay.

Somatic gene mutation and human disease other than cancer

While the focus of much mutation research is on germ-line mutation, somatic mutation is being found to be important in human disease. Neurofibromatosis 1 and McCune-Albright are disorders which are detected in the skin and other systems. The skin manifestations were essential for the demonstration of somatic mosaicism in neurofibromatosis 1, while analysis of blood DNA demonstrated somatic mutation in neurofibromatosis 2. Incontinentia pigmenti is also a disorder seen in skin and other tissues, but here it is the rare variant of the disorder in males, where it is usually lethal, that involves somatic mosaicism. Paroxysmal nocturnal hemoglobinuria is a disorder of the blood and cell separation of blood elements allows the demonstration of the somatic mosaicism. This review also discusses disorders in which somatic mosaicism, for mutations probably incompatible with life if the mutation had been germ-line, are likely to be involved. These include the Proteus syndrome, which involves both vascular tissues and bones, and two disorders which might be thought of as representing two subtypes of Proteus: Klippel-Trenaunay, which involves vascular tissues, and Maffuci, which involves bones. Embryonic mutations, which create mosaicism for both the soma and germ-line, are being increasingly found in a number of disorders and are discussed more briefly. Finally, reverse mutations involving the soma have been recently found in several disorders and such revertant mutations are also examined. While the review focuses on the clinical importance of somatic mutations, many of the mutations found to date are tabulated. It is too early to see if there is a different pattern of somatic mutation as compared to germ-line mutation. Although the parameters to allow careful quantitation are not yet available, it seems that the frequency of gene mutation in embryonic cells is not markedly different than that in the germ-line.

Albright's hereditary osteodystrophy and pseudohypoparathyroidism

Pseudohypoparathyroidism (PHP) and Albright's hereditary osteodystrophy (AHO) are not interchangeable terms. AHO describes a constellation of physical features, including short adult stature, obesity, brachydactyly, and ectopic ossifications. PHP means end-organ resistance to PTH and is subclassified into types Ia, Ib, and Ic and type II. Pseudopseudohypoparathyroidism (PPHP) is a term used for individuals with AHO who have normal end-organ responses to PTH. Both the PHPIa and PPHP forms of AHO result from heterozygous deactivating mutations in the GNAS1 gene associated with a 50% reduction in bioactivity of the Gsalpha protein that it encodes. The GNAS1 gene is subject to tissue-specific genomic imprinting. Patients with mutations on their maternally derived allele are likely to have associated PHPIa, whereas mutations on the paternal allele usually cause PPHP. Isolated PTH resistance (PHPIb) can result from mutations within the GNAS1 gene but is more commonly caused by epigenetic imprinting abnormalities affecting the upstream exon 1A. The causes of PHP type Ic and PHP type II are not yet clear, and the latter is likely to be heterogeneous.

Constitutional deletion of chromosome 20q in two patients affected with albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) results from heterozygous inactivation of G(s)alpha, encoded by the GNAS1 locus on the distal long arm of chromosome 20. This autosomal dominant condition is characterized by short stature, obesity, shortening of the metacarpals and metatarsals, and variable mental retardation and may also include end-organ resistance to multiple hormones. Small insertions and deletions or point mutations of GNAS1 are found in approximately 80% of patients with AHO. The remainder may be accounted for by larger genomic rearrangements, but none have been reported to date. We now describe two patients with constitutional 20q deletions and features of AHO. Such deletions are rare in the published literature and have not previously been associated with AHO. Molecular genetic analysis confirmed complete deletion of GNAS1 in both patients. Parental origin could be determined in both cases and provides further support for the parent-of-origin effect on the biochemical status of patients with AHO.

Characterization of gsp-mediated growth hormone excess in the context of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a disorder characterized by the triad of café-au-lait skin pigmentation, polyostotic fibrous dysplasia of bone, and hyperfunctioning endocrinopathies, including GH excess. The molecular etiology of the disease is postzygotic activating mutations of the GNAS1 gene product, G(s)alpha. The term gsp oncogene has been assigned to these mutations due to their association with certain neoplasms. The aim of this study was to estimate the prevalence of GH excess in MAS, characterize the clinical and endocrine manifestations, and describe the response to treatment. Fifty-eight patients with MAS were screened, and 22 with stigmata of acromegaly and/or elevated GH or IGF-I underwent oral glucose tolerance testing. Twelve patients (21%) had GH excess, based on failure to suppress serum GH on oral glucose tolerance test, and underwent a TRH test, serial GH sampling from 2000-0800 h, and magnetic resonance imaging of the sella. We found that vision and hearing deficits were more common in patients with GH excess (4 of 12, 33%) than those without (2 of 56, 4%). Of interest, patients with a history of precocious puberty and GH excess who had reached skeletal maturity achieved normal adult height despite a history of early epiphyseal fusion. All 9 patients tested had an increase in serum GH after TRH, 11 of 12 (92%) had hyperprolactinemia, and all 8 tested had detectable or elevated nighttime GH levels. Pituitary adenoma was detected in 4 of 12 (33%) patients. All patients with elevated IGF-I levels were treated with cabergoline (7 patients), long-acting octreotide (LAO; 8 patients), or a combination of cabergoline and LAO (4 patients). In six of the seven patients (86%) treated with cabergoline, serum IGF-I decreased, but not to the normal range. In the eight patients treated with LAO alone, IGF-I decreased, and, in four, returned to the normal range. The remaining 4 patients were treated with a combination of cabergoline and LAO. For them, symptoms of GH excess diminished, and IGF-I decreased further, but did not enter the normal range. GH excess is common in MAS and results in a distinct clinical phenotype characterized by inappropriately normal stature, TRH responsiveness, prolactin cosecretion, small or absent pituitary tumors, a consistent but inadequate response to treatment with cabergoline, and an intermediate response to LAO.

A novel, complex heterozygous mutation within Gsalpha gene in patient with McCune-Albright syndrome

McCune-Albright syndrome (MAS) is caused by embryonic somatic mutations leading to the substitution of His or Cys for Arg at amino acid 201 of the alpha-subunit of the signal transduction protein Gs (Gsalpha). The mutations have been found in many affected tissues of patients with MAS. Recently, a new missense mutation was detected in a patient with MAS, leading to the substitution of glycine for arginine at amino acid 201 of the Gsalpha gene, whereas no mutations have been reported at other sites in this gene. In the present study, we identified the activating mutations in the gene encoding Gsalpha protein in the osseous lesions of fibrous dysplasia and peripheral blood leukocyte in a 17-yr-old male patient with MAS. In addition, a heterozygous mutation encoding substitution of Arg201 of Gsalpha with His was found. Interestingly, we also found the other two types of mutations within the Gsalpha gene in the patient's affected osseous tissue. One is a combination mutation in the same allele at codons 209 and 210 of the Gsalpha gene, and the other the missense mutation at codon 235.

Gs(alpha) mutations and imprinting defects in human disease

Gs is the ubiquitously expressed heterotrimeric G protein that couples receptors to the effector enzyme adenylyl cyclase and is required for receptor-stimulated intracellular cAMP generation. Activated receptors promote the exchange of GTP for GDP on the Gs alpha-subunit (Gs(alpha)), resulting in Gs activation; an intrinsic GTPase activity of Gs(alpha) deactivates Gs by hydrolyzing bound GTP to GDP. Mutations of Gs(alpha) residues involved in the GTPase reaction that lead to constitutive activation are present in endocrine tumors, fibrous dysplasia of bone, and McCune-Albright syndrome. Heterozygous loss-of-function mutations lead to Albright hereditary osteodystrophy (AHO), a disease characterized by short stature, obesity, and skeletal defects, and are sometimes associated with progressive osseous heteroplasia. Maternal transmission of Gs(alpha) mutations leads to AHO plus resistance to several hormones (e.g., parathyroid hormone) that activate Gs in their target tissues (pseudohypoparathyroidism type IA), while paternal transmission leads only to the AHO phenotype (pseudopseudohypoparathyroidism). Studies in both mice and humans demonstrate that Gs(alpha) is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in some tissues and biallelically expressed in most other tissues. This likely explains why multihormone resistance occurs only when Gs(alpha) mutations are inherited maternally. The Gs(alpha) gene GNAS1 has at least four alternative promoters and first exons, leading to the production of alternative gene products including Gs(alpha), XL alphas (a novel Gs(alpha) isoform expressed only from the paternal allele), and NESP55 (a chromogranin-like protein expressed only from the maternal allele). The fourth alternative promoter and first exon (exon 1A) located just upstream of the Gs(alpha) promoter is normally methylated on the maternal allele and is transcriptionally active on the paternal allele. In patients with parathyroid hormone resistance but without AHO (pseudohypoparathyroidism type IB), the exon 1A promoter region is unmethylated and transcriptionally active on both alleles. This GNAS1 imprinting defect is predicted to decrease Gs(alpha) expression in tissues where Gs(alpha) is normally imprinted and therefore to lead to renal parathyroid hormone resistance.

McCune-Albright syndrome: radiological and MR findings

McCune-Albright syndrome (MAS) is a non-inherited disorder due to the GNAS1 gene mutation. The syndrome is characterized with the triad of polyostotic fibrous dysplasia, pigmented skin lesions, endocrinopathy, and precocious puberty. We report the case of a 14-year-old boy, presenting with sclerotic type of polyostotic fibrous dysplasia. Radiological methods including plain X-ray film, MR and whole body bone scintigraphy suggested the diagnosis of MAS. MRI provided more directly perceived images and it was more sensitive in demonstrating the lesion: its shape, contents, especially the size of the affected region. Histopathological study and the identification of mutant gene finally confirmed the diagnostic result.

Premature thelarche and granulosa cell tumors: a search for FSH receptor and G5alpha activating mutations

Activating mutations of the Gsalpha gene are responsible for McCune-Albright syndrome and have also been identified in sporadic tumors of the pituitary and thyroid. When associated with malignancy, activating Gsalpha mutations are known as gsp-oncogenes. We hypothesized that similar activating mutations might also account for some cases of premature thelarche and/ or granulosa cell tumors. Polymerase chain reaction and DNA sequencing was used to screen for activating mutations of Gsalpha genes in children with premature thelarche and in pathologic specimens from juvenile and adult granulosa cell tumors. Because these disorders involve over-activity of the FSH-signaling pathway, we also screened for activating mutations of the FSH receptor. No mutations were detected in either the Gsalpha or the FSHR fragment studied. Previously reported polymorphisms (Ser680Asn and Ala307Thr) of the FSHR were detected in 25/27 tumor samples and 9/9 premature thelarche samples. We conclude that activating mutations in previously identified mutation 'hot-spots' in the Gsalpha and FSH receptor genes are probably not a major cause of premature thelarche or granulosa cell tumors. In contrast, polymorphisms of the FSH receptor are common.

GNAS1 lesions in pseudohypoparathyroidism Ia and Ic: genotype phenotype relationship and evidence of the maternal transmission of the hormonal resistance

We conducted clinical and biological studies including screening for mutations in the gene encoding the alpha subunit of G(s) (GNAS1) in 30 subjects (21 unrelated families) with Albright's hereditary osteodystrophy (AHO), pseudohypoparathyroidism (PHP); and decreased erythrocyte G(s) activity (PHP-Ia; n = 19); AHO and decreased erythrocyte G(s) activity (isolated AHO; n = 10); or AHO, hormonal resistance, and normal erythrocyte G(s) activity (PHP-Ic; n = 1). A heterozygous GNAS1 gene lesion was found in 14 of 17 PHP-Ia index cases (82%), including 11 new mutations and a mutational hot-spot involving codons 189-190 (21%). These lesions lead to a truncated protein in all but three cases with missense mutations R280K, V159M, and D156N. In the patient diagnosed with PHP-Ic, G(s)alpha protein was shortened by just four amino acids, a finding consistent with the conservation of G(s) activity in erythrocytes and the loss of receptor contact. No GNAS1 lesions were found in individuals with isolated AHO that were not relatives to PHP-Ia patients (n = 5). Intrafamilial segregation analyses of the mutated GNAS1 allele in nine PHP-Ia patients established that the mutation had either occurred de novo on the maternal allele (n = 4) or had been transmitted by a mother with a mild phenotype (n = 5). This finding is consistent with an imprinting of GNAS1 playing a role in the clinical phenotype of loss of function mutations and with a functional maternal GNAS1 allele having a predominant role in preventing the hormonal resistance of PHP-Ia.

Searching for Arg201 mutations in the GNAS1 gene in Italian patients with McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a rare disease caused by somatic postzygotic mutations at Arg201 in the GNAS1 gene that encodes for the Gsalpha protein. Arg201 mutations are gain-of-function mutations in affected tissues (including bone, skin, endocrine glands and other tissues) that result in the activation of cAMP. We used a polymerase chain reaction(PCR)-based technique for the selective enrichment and analysis of the Arg201 mutant allele in 27 different tissues from 24 Italian patients with one or more signs of MAS. Arg201 mutations were identified in 13 different tissues (48.1%) from 11 patients (45.8%). Mutation detection rates differed across the various types of tissue samples, and the mutation was not always found in every tissue sample from the same patient. To overcome problems in the analysis of mutations in somatic mosaicism, as occurs in MAS, a highly sensitive molecular technique should be applied, the most appropriate tissue source selected, and various affected tissues from the same patient analyzed.

McCune-Albright syndrome: molecular genetics

McCune-Albright syndrome (MAS) is a rare disorder characterized by the association of precocious puberty (mostly in girls), polyostotic fibrous dysplasia and café-au-lait pigmented skin lesions. In addition to this classical triad, several endocrine disorders, all due to autonomous hormonal hyperproduction, can also be associated, such as pituitary adenomas secreting growth hormone, hyperthyroid goiters, or adrenal hyperplasia. The distribution pattern of skin lesions and the sporadic character of MAS have led to the hypothesis that this syndrome is due to a dominant somatic mutation early in the course of development. Furthermore, the diverse endocrine hyperactivity syndromes observed in MAS have in common the involvement of cells that respond to extracellular signaling by activating the adenyl cyclase system. The identification of somatic mutations of the Gsalpha gene have shown that MAS is due to a post-zygotic activating mutation of the Gsalpha subunit leading to a mosaic distribution of cells bearing constitutively active adenyl cyclase activity. In all patients reported to date, the mutation is a substitution of the arginine residue at position 201 most often into histidine or cysteine. We present here some of the results we have obtained in studying 80 patients presenting one or several signs of MCA for identification of the Arg201 mutation. We used a PCR-based method that allows selective enrichment of mutated DNA. This study, and data in the literature during the last decade, has widened the definition of MAS. Affections as clinically different as somatotropic or thyrotropic adenomas, isolated polyostotic fibrous dysplasia, isolated peripheral precocious puberty and the classic McCune-Albright syndrome all appear to be elements of a wide spectrum of disease based on the same molecular defect. The developmental moment at which the mutation occurs determines both the number of tissues affected and the severity of expression. The application of tools from molecular genetics to the study of this syndrome confirms their essential contribution to a deeper understanding of endocrine pathologies.

[Clinical and molecular study of Chilean patients with McCune-Albright syndrome]

BACKGROUND

McCune-Albright Syndrome (MAS) is characterized by precocious puberty, "cafe au lait" skin lesions and polyostotic fibrous dysplasia. It is caused by 4 post-zygotic mutations of G alpha s protein with a mosaic distribution.

AIM

To describe the clinical presentation and to investigate the presence of the Arg by his substitution (R201H) in 14 girls with MAS.

PATIENTS AND METHODS

We performed a clinical analysis of the patients and specific allele PCR in DNA obtained from leukocytes.

RESULTS

Twelve of 14 patients presented with precocious puberty, one with cyclical vaginal bleeding and one with pathological bone fractures. Eight girls had polyostotic fibrous dysplasia, one had hyperthyroidism, four had pathological fractures, ten had ovarian cysts, six had breast hyperpigmentation and ten had "cafe au lait" skin lesions. We detected the R2O1H mutation in 10 of 14 patients. We found no difference in the severity of symptoms or in the age of presentation between the patients with and without the mutation.

CONCLUSIONS

The R201H mutation can be detected in white blood cells, in approximately 70% of cases. Patients exhibit wide clinical variability with the same molecular defect. This suggests that tissues have different proportions of mutant cells.

Immunoexpression of neurofibromin, S-100 protein, and leu-7 and mutation analysis of the NF1 gene at codon 1423 in osteofibrous dysplasia

The NF1 (neurofibromatosis type 1, or von Recklinghausen disease) gene, is a tumor-suppressor gene, and its product, neurofibromin, down-regulates ras protein by its guanosine triphosphatase-activating protein (GAP)-related domain. Osteofibrous dysplasia (OFD) is characterized by fibroblast-like spindle cells and osseous tissue and is generally seen in the tibia or fibula during childhood. The precise nature of OFD remains controversial. Cosegregations of OFD and NF1 have been reported, and it has been surmised that OFD is associated with the NF1 gene. We studied the expressions of NF1 gene product (neurofibromin) and so-called Schwann cell markers (S-100 protein, Leu-7) in 17 cases of OFD immunohistochemically. Ten cases of fibrous dysplasia (FD) were also used for the purpose of comparison. Five OFD and 7 FD cases were analyzed for NF1 gene mutation at codon 1423, which is a GAP-related domain, by single-strand conformation polymorphism. Fibroblast-like cells of OFD showed the expression of neurofibromin (5 of 17), S-100 protein (9 of 17), and Leu-7 (5 of 17), and those of FD did not show these expressions, with the exception of 1 case that showed Leu-7 expression. Regarding the OFD cases, significant correspondence was found between cases showing expression of neurofibromin and S-100 protein, between cases showing expression of neurofibromin and Leu-7, and between cases showing expression of S-100 protein and Leu-7 (P < .01). NF1 gene mutation at codon 1423 was not detected in either the OFD (0 of 5) or FD (0 of 7) cases. These results seem to suggest the possible involvement of neurofibromin in the development of OFD, which is associated with the expression of Schwann cell markers (S-100 protein and Leu-7). Furthermore, NF1 gene mutation at codon 1423 did not seem to be related to OFD.

Gnathodiaphyseal dysplasia: a syndrome of fibro-osseous lesions of jawbones, bone fragility, and long bone bowing

We report an unusual generalized skeletal syndrome characterized by fibro-osseous lesions of the jawbones with a prominent psammomatoid body component, bone fragility, and bowing/sclerosis of tubular bones. The case fits with the emerging profile of a distinct syndrome with similarities to previously reported cases, some with an autosomal dominant inheritance and others sporadic. We suggest that the syndrome be named gnathodiaphyseal dysplasia. The patient had been diagnosed previously with polyostotic fibrous dysplasia (PFD) elsewhere, but further clinical evaluation, histopathological study, and mutation analysis excluded this diagnosis. In addition to providing a novel observation of an as yet poorly characterized syndrome, the case illustrates the need for stringent diagnostic criteria for FD. The jaw lesions showed fibro-osseous features with the histopathological characteristics of cemento-ossifying fibroma, psammomatoid variant. This case emphasizes that the boundaries between genuine GNAS1 mutation-positive FD and other fibro-osseous lesions occurring in the jawbones should be kept sharply defined, contrary to a prevailing tendency in the literature. A detailed pathological study revealed previously unreported features of cemento-ossifying fibroma, including the participation of myofibroblasts and the occurrence of psammomatoid bodies and aberrant mineralization, within the walls of blood vessels. Transplantation of stromal cells grown from the lesion into immunocompromised mice resulted in a close mimicry of the native lesion, including the sporadic formation of psammomatoid bodies, suggesting an intrinsic abnormality of bone-forming cells.

Cellular and molecular basis of fibrous dysplasia

Recent advances have been made in the cellular and molecular mechanisms involved in monostotic and polyostotic fibrous dysplasia, a rare nonmalignant disease causing bone deformations and fractures. The molecular basis of fibrous dysplasia has been clarified when mutations affecting the stimulatory alpha subunit of G protein (Gs) have been found in dysplastic bone lesions. The histological analysis of dysplastic lesions revealed that the mutations in Gsalpha caused abnormalities in cells of the osteoblastic lineage and therefore in the bone matrix. Further in vitro analyses of bone cells from mutant dysplastic bone lesions revealed that the abnormal deposition of immature bone matrix in fibrous dysplasia results from decreased differentiation and increased proliferation of osteoblastic cells. Finally, the signaling pathway involved in these osteoblastic abnormalities has been identified. It is now apparent that the constitutive elevation in cAMP level induced by the Gsalpha mutations leads to alterations in the expression of several target genes whose promoters contain cAMP-responsive elements, such as c-fos, c-jun, Il-6 and Il-11. This in turn affects the transcription and expression of downstream genes and results in the alterations of osteoblast recruitment and function in dysplastic bone lesions. These mechanisms provide a cellular and molecular basis for the alterations in bone cells and bone matrix in fibrous dysplasia.

[Albright hereditary osteodystrophy: identification of a novel mutation in a family]

Studies to detect mutations in the GNAS1 gene were performed in a male patient with features of Albright hereditary osteodystrophy and resistance of target tissues to parathyroid hormone (Pseudohypoparathyroidism Ia). The same investigations were carried out in the patient's mother who showed somatic features of Albright's hereditary osteodystrophy and brachymetacarpia without resistance to parathyroid hormone (Pseudopseudohypoparathyroidism). A point mutation designated c.794GA (R265H) in exon 10 of GNAS1 was identified in DNA from the patient and his mother. This novel mutation in exon 10 of GNA

Activating and inactivating mutations in the human GNAS1 gene

GNAS1 on chromosome 20 is a complex locus, encoding multiple proteins, of which G(s)alpha, the alpha-subunit of the heterotrimeric stimulatory G protein G(s), is of particular interest clinically. Amino acid substitutions at two specific codons lead to constitutive activation of G(s)alpha. Such gain-of-function mutations are found in a variety of sporadic endocrine tumors and in McCune-Albright syndrome, a sporadic condition characterized by multiple endocrine abnormalities. Heterozygous loss of G(s)alpha function results in the dominantly inherited condition, Albright hereditary osteodystrophy (AHO). Here we present a review of published GNAS1 mutations and report 19 additional mutations, of which 15 are novel. A diverse range of inactivating mutations has been detected, scattered throughout the gene but showing some evidence of clustering. Only one, a recurring 4 bp deletion in exon 7, could be considered common among AHO patients. The parental origin of the mutation apparently determines whether or not the patient shows end-organ resistance to hormones such as parathyroid hormone. G(s)alpha is biallelically expressed in all tissues studied to date and thus there is no direct evidence that this transcript is imprinted. However, the recent identification of other imprinted transcripts encoded by GNAS1 and overlapping G(s)alpha, together with at least one imprinted antisense transcript, raises intriguing questions about how the primary effect of mutations in GNAS1 might be modulated.

Activating mutation of GS alpha in McCune-Albright syndrome causes skin pigmentation by tyrosinase gene activation on affected melanocytes

McCune-Albright syndrome (MAS) is a sporadic disease characterized by café-au-lait spots, polyostotic fibrous dysplasia and hyperfunctional endocrinopathies. To elucidate the mechanism of skin pigmentation, melanocytes, keratinocytes and fibroblasts were primary cultured from the café-au-lait spot of a MAS patient. Then, mutational analysis and morphologic evaluation were performed. Also, cAMP level and tyrosinase gene expression in cultured cells were determined. Only Gsalpha mutation was found in affected melanocytes and the cAMP level in affected melanocytes was higher than that of normal melanocytes. The mRNA expression of tyrosinase gene was increased in the affected melanocytes. This study suggests that skin pigmentation of MAS results from activating mutation of Gsalpha in melanocytes and the mechanism involves the c-AMP-mediated tyrosinase gene activation.

Inverted duplications are recurrent rearrangements always associated with a distal deletion: description of a new case involving 2q

We studied the case of a subject with an inverted duplication of 40 cM of 2q33-q37 concurrent with a 10 cM deletion of the distal 2q, the latter not being detectable by cytogenetics. Microsatellite analysis demonstrated the absence of maternal alleles in the deleted region and a double dosage for one of the maternal alleles in the duplication region. We hypothesised that this type of rearrangement occurs at meiosis I, while the two homologues are synapsed for most of their length. The presence of inverted duplicons in the same chromosome arm would favour the partial refolding of one homologue into itself so leading to the intrachromatid synapsis and recombination of the inverted repeats. The arising recombinant chromosome is deleted for the region beyond the most distal repeat and with the chromatids joined together at the level of the region located between the two duplicons. At meiosis II, the two linked chromatids can join the opposite poles provided that a breakage between the two centromeres occurs leading to a duplicated/deleted chromosome and a simply deleted chromosome. This model can be extended to all the so-called inverted duplication cases and to part of the terminal deletions. In fact the finding that, in our invdup(2q), the entire 40 cM duplication region involves only one of the two maternal alleles, indeed indicates that the abnormal crossover occurs between sister chromatids. The phenotype associated with our 2q rearrangement led us to narrow the critical region for the Albright-like syndrome to 10 cM in the subterminal 2q region.

Osteogenic induction in hereditary disorders of heterotopic ossification

The formation of heterotopic bone within soft connective tissue is a common feature of at least three distinct genetic disorders of osteogenesis in humans: fibrodysplasia ossificans progressiva; progressive osseous heteroplasia; and Albright hereditary osteodystrophy. The pathobiologic characteristics of osteogenic induction, the histopathologic features of osteogenesis, the anatomic distribution of heterotopic lesions, and the developmental patterns of disease progression differ among all three conditions. The molecular and cellular basis of redirecting a mature connective tissue phenotype to form bone is a remarkable biological phenomenon with enormous implications for the control of bone regeneration, fracture healing, and disorders of osteogenesis.

A comparative study of fibrous dysplasia and osteofibrous dysplasia with regard to Gsalpha mutation at the Arg201 codon: polymerase chain reaction-restriction fragment length polymorphism analysis of paraffin-embedded tissues

Fibrous dysplasia and osteofibrous dysplasia are both benign fibro-osseous lesions of the bone and are generally seen during childhood or adolescence. Histologically, the features of these bone lesions sometimes look quite similar, but their precise nature remains controversial. Mutation of the alpha subunit of signal-transducing G proteins (Gsalpha), with an increase in cyclic adenosine monophosphate (cAMP) formation, has been implicated in the development of multiple endocrinopathies of the Albright-McCune syndrome and in the development of fibrous dysplasia. We studied Gsalpha mutation at the Arg201. codon in seven cases of fibrous dysplasia (six monostotic lesions and one polyostotic lesion) and seven cases of osteofibrous dysplasia using formalin-fixed, paraffin-embedded tissue, by means of polymerase chain reaction-restriction fragment length polymorphism and direct sequencing analysis. All of the seven cases of fibrous dysplasia showed missense point mutations in Gsalpha at the Arg201 codon that resulted in Arg-to-His substitution in three cases and Arg-to-Cys substitution in four cases. On the other hand, the seven cases of osteofibrous dysplasia and the normal bone used as a control showed no such mutation. These data suggest that fibrous dysplasia and osteofibrous dysplasia have different pathogeneses and that the detection of Gsalpha mutation at the Arg201 codon is quite useful for distinguishing between these lesions.

Variable imprinting of the heterotrimeric G protein G(s) alpha-subunit within different segments of the nephron

The heterotrimeric G protein G(s) is required for hormone-stimulated intracellular cAMP generation because it couples hormone receptors to the enzyme adenylyl cyclase. Hormones that activate G(s) in the kidney include parathyroid hormone, glucagon, calcitonin, and vasopressin. Recently, it has been demonstrated that the G(s)alpha gene is imprinted in a tissue-specific manner, leading to preferential expression of G(s)alpha from the maternal allele in some tissues. In the kidney, G(s)alpha is imprinted in the proximal tubule but not in more distal nephron segments, such as the thick ascending limb or collecting duct. This most likely explains why in both humans and mice heterozygous mutations in the maternal allele lead to parathyroid hormone resistance in the proximal tubule whereas mutations in the paternal allele do not. In contrast, heterozygous mutations have little effect on vasopressin action in the collecting ducts. In mice with heterozygous null G(s)alpha mutations (both those with mutations on the maternal or paternal allele), expression of the Na-K-2Cl cotransporter was decreased in the thick ascending limb, suggesting that its expression is regulated by cAMP. The G(s)alpha genes also generate alternative, oppositely imprinted transcripts encoding XLalphas, a G(s)alpha isoform with a long NH(2)-terminal extension, and NESP55, a chromogranin-like neurosecretory protein. The role, if any, of these proteins in renal physiology is unknown.

Pseudohypoparathyroidism type Ia. Albright hereditary osteodystrophy: a model for research on G protein-coupled receptors and genomic imprinting

Pseudohypoparathyroidism type Ia (PHP Ia) is a hereditary endocrine disorder, characterised by resistance to parathyroid hormone (PTH), causing disturbance of calcium homeostasis, and to several other polypeptide hormones. Patients with PHP Ia exhibit a complex of somatic abnormalities, termed Albright hereditary osteodystrophy (AHO). Treatment with vitamin D derivatives alleviates symptoms of hypocalcemia and may prevent bone demineralisation. PTH, like many polypeptide hormones, exerts its effects via a G protein-coupled cell surface receptor. PHP Ia is caused by a heterozygous, inactivating mutation in the gene for the alpha-subunit of the Gs protein, which disrupts Gs-protein-coupled signal transduction pathways. Several mutations have been described. When the mutation is inherited from the mother, the offspring will develop PHP Ia, i.e., both hormonal resistance and somatic abnormalities. When the mutation is derived from the father, children will have normal hormone responses while exhibiting the somatic features of AHO; this form of the disorder is called pseudopseudohypoparathyroidism (PPHP). A combination of tissue-specific genomic imprinting and haploinsufficiency may explain the occurrence of PPHP, and the fact that not all Gs-mediated polypeptide hormone actions are affected equally. PHP may therefore serve as a model in studying the pleiotropic consequences of impaired Gs-mediated signal transduction.