Identification of a mutation in the gene encoding the alpha subunit of the stimulatory G protein of adenylyl cyclase in McCune-Albright syndrome

Consensus statement by the French Society of Endocrinology (SFE) and French Society of Pediatric Endocrinology & Diabetology (SFEDP) for the diagnosis of Cushing's syndrome: Genetics of Cushing's syndrome

Cushing's syndrome is due to overproduction of cortisol, leading to abnormal and prolonged exposure to cortisol. The most common etiology is Cushing disease, while adrenal causes are rarer. Knowledge of the genetics of Cushing's syndrome, and particularly the adrenal causes, has improved considerably over the last 10 years, thanks in particular to technical advances in high-throughput sequencing. The present study, by a group of experts from the French Society of Endocrinology and the French Society of Pediatric Endocrinology and Diabetology, reviewed the literature on germline genetic alterations leading to a predisposition to develop Cushing's syndrome. The review led to a consensus statement on genetic screening for Cushing disease and adrenal Cushing's syndrome.

Genetic characterization of intramuscular myxomas

Introduction: Intramuscular myxomas are benign tumors that are challenging to diagnose, especially on core needle biopsies. Acquired chromosomal aberrations and pathogenic variants in codon 201 or codon 227 in GNAS complex locus gene (GNAS) have been reported in these tumors. Here we present our genetic findings in a series of 22 intramuscular myxomas. Materials and methods: The tumors were investigated for the presence of acquired chromosomal aberrations using G-banding and karyotyping. Pathogenic variants in codon 201 or codon 227 of GNAS were assessed using direct cycle Sanger sequencing and Ion AmpliSeq Cancer Hotspot Panel v2 methodologies. Results: Eleven tumors carried chromosomal abnormalities. Six tumors had numerical, four had structural, and one had both numerical and structural chromosomal aberrations. Gains of chromosomes 7 and 8 were the most common abnormalities being found in five and four tumors respectively. Pathogenic variants in GNAS were detected in 19 myxomas (86%) with both methodologies. The detected pathogenic variants were p.R201H in nine cases (seven with abnormal and two with normal karyotypes), p.R201C in five cases, all with normal karyotypes, p.R201S in three cases (two with abnormal and one with normal karyotype), p.R201G in one case with a normal karyotype, and p.Q227E in one case with a normal karyotype. Conclusion: Firstly, our data indicate a possible association between chromosomal abnormalities and GNAS pathogenic variants in intramuscular myxomas. Secondly, the presence of the rare pathogenic variants R201S, p.R201G and p.Q227E in 26% (5 out of 19) of myxomas with GNAS pathogenic variants shows that methodologies designed to detect only the common "hotspot" of p.R201C and p.R201H will give false negative results. Finally, a comparison between Ion AmpliSeq Cancer Hotspot Panel v2 and direct cycle Sanger sequencing showed that direct cycle Sanger sequencing provides a quick, reliable, and relatively cheap method to detect GNAS pathogenic variants, matching even the most cutting-edge sequencing methods.

Genetic testing in prolactinomas: a cohort study

BACKGROUND

Prolactinomas represent 46%-66% of pituitary adenomas, but the prevalence of germline mutations is largely unknown. We present here the first study focusing on hereditary predisposition to prolactinoma.

OBJECTIVE

We studied the prevalence of germline mutations in a large cohort of patients with isolated prolactinomas.

MATERIALS AND METHODS

A retrospective study was performed combining genetic and clinical data from patients referred for genetic testing of MEN1, AIP, and CDKN1B between 2003 and 2020. SF3B1 was Sanger sequenced in genetically negative patients.

RESULTS

About 506 patients with a prolactinoma were included: 80 with microprolactinoma (15.9%), 378 with macroprolactinoma (74.7%), 48 unknown; 49/506 in a familial context (9.7%). Among these, 14 (2.8%) had a (likely) pathogenic variant (LPV) in MEN1 or AIP, and none in CDKN1B. All positive patients had developed a macroprolactinoma before age 30. The prevalence of germline mutations in patients with isolated macroprolactinoma under 30 was 4% (11/258) in a sporadic context and 15% (3/20) in a familial context. Prevalence in sporadic cases younger than 18 was 15% in men (5/33) and 7% in women (4/57). No R625H SF3B1 germline mutation was identified in 264 patients with macroprolactinomas.

CONCLUSIONS

We did not identify any LPVs in patients over 30 years of age, either in a familial or in a sporadic context, and in a sporadic context in our series or the literature. Special attention should be paid to young patients and to familial context.

Identification of GNAS Variants in Circulating Cell-Free DNA from Patients with Fibrous Dysplasia/McCune Albright Syndrome

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare mosaic bone and endocrine disorder. Although most variants affect the GNAS R201 codon, obtaining a genetic diagnosis is difficult because not all cells harbor the variant, and an invasive biopsy may be required. We explored the presence of GNAS p.R201 variants in blood circulating cell free DNA (ccfDNA) using sensitive techniques of digital droplet polymerase chain reaction (PCR) (ddPCR) and competitive allele-specific TaqMan PCR (castPCR) in an effort to improve the genetic diagnosis of FD/MAS. We isolated ccfDNA from the plasma of 66 patients with a wide range of disease severity and performed both ddPCR and castPCR mutation analysis to search for GNAS p.R201H or R201C variants. We detected R201 variants in ccfDNA samples of 41 of 66 (62.1%) patients by either castPCR or ddPCR, and 45 of 66 (68.2%) of patients if the techniques were combined. Variant detection was more likely in patients with more severe disease. Skeletal disease burden score (SBS) was significantly higher in patients who had detectable variants, and SBS was a predictor of variant allele frequency. By ddPCR analysis, patients aged ≤30 years had higher detection rates, and higher variant allele frequencies, independent of disease burden. We detected variant DNA in only one patient with monostotic FD by ddPCR only. In summary, we have demonstrated that ccfDNA containing variant GNAS can be isolated from the plasma of patients with FD/MAS and that ddPCR and castPCR methods have similar variant detection rates. This methodology represents an important potential advancement in diagnosis for patients with FD/MAS, especially those younger than 30 years or with more severe disease. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Structural and Functional Implication of Natural Variants of Gαs

Heterotrimeric guanine nucleotide-binding proteins (G proteins) are among the most important cellular signaling components, especially G protein-coupled receptors (GPCRs). G proteins comprise three subunits, Gα, Gβ, and Gγ. Gα is the key subunit, and its structural state regulates the active status of G proteins. Interaction of guanosine diphosphate (GDP) or guanosine triphosphate (GTP) with Gα switches G protein into basal or active states, respectively. Genetic alteration in Gα could be responsible for the development of various diseases due to its critical role in cell signaling. Specifically, loss-of-function mutations of Gαs are associated with parathyroid hormone-resistant syndrome such as inactivating parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) signaling disorders (iPPSDs), whereas gain-of-function mutations of Gαs are associated with McCune-Albright syndrome and tumor development. In the present study, we analyzed the structural and functional implications of natural variants of the Gαs subtype observed in iPPSDs. Although a few tested natural variants did not alter the structure and function of Gαs, others induced drastic conformational changes in Gαs, resulting in improper folding and aggregation of the proteins. Other natural variants induced only mild conformational changes but altered the GDP/GTP exchange kinetics. Therefore, the results shed light on the relationship between natural variants of Gα and iPPSDs.

Case report: Surgical treatment of McCune-Albright syndrome with hyperthyroidism and retrosternal goiter: A case report and literature review

Introduction

McCune-Albright syndrome (MAS) is a low-incidence syndrome consisting of the clinical triad of fibrous structural dysplasia of bone, endocrine disease, and skin pigmentation. Thyroid dysfunction is the second most common endocrine dysregulation in MAS. However, there are no treatment guidelines for MAS complicated with hyperthyroidism. Notably, no case of MAS complicated with retrosternal goiter and hyperthyroidism has been reported to our knowledge.

Case presentation

We report a 27-year-old man with MAS who developed the typical triad of bone fibrous dysplasia, skin pigmentation and hyperthyroidism, complaining of recent fast-growing neck mass and difficulty in breathing. Hyperthyrodism was under control by Thiamazole, and computed tomography showed an enlarged thyroid extending retrosternally. We performed a total thyroidectomy on the patient. At the 1-year follow-up, the patient's dyspnea, hyperthyroidism, and bone pain were all significantly alleviated.

Review

We searched the literature for previous case reports concerning MAS patients complicated with thyroid dysregulation. A total of 17 articles and 22 patients were identified to form our database. Among them, 9 studies clearly mentioned surgical intervention in 11 patients, and prognoses were also reported. Surgery was the most common intervention chosen and indicated a satisfactory prognosis.

Conclusion

We report a rare case of MAS patient complicated with retrosternal goiter and hyperthyroidism. Our review provides an overview of MAS cases requiring interventions on thyroid function, and total thyroidectomy should be a proper treatment for these patients.

Phosphatonins: From Discovery to Therapeutics

OBJECTIVE

Phosphate is crucial for cell signaling, energy metabolism, nucleotide synthesis, and bone mineralization. The gut-bone-parathyroid-kidney axis is influenced by parathyroid hormone, 1,25-dihydroxyvitamin D, and phosphatonins, especially fibroblast growth factor 23 (FGF23). These hormones facilitate maintenance of phosphate homeostasis. This review summarizes current knowledge regarding the phosphate homeostasis, phosphatonin pathophysiology, and clinical implications of FGF23-related hypophosphatemic disorders, with specific focus on burosumab treatment.

METHOD

A focused literature search of PubMed was conducted.

RESULTS

Phosphatonins including FGF23, secreted frizzled-related protein 4, matrix extracellular phosphoglycoprotein, and fibroblast growth factor 7 play a pathogenic role in several hypophosphatemic disorders. Excess FGF23 inhibits sodium-dependent phosphate cotransporters (NaPi-2a and NaPi-2c), resulting in hyperphosphaturia and hypophosphatemia. Additionally, FGF23 suppresses 1,25-dihydroxyvitamin D synthesis in the proximal renal tubule, and thus, it indirectly inhibits intestinal phosphate absorption. Disorders of FGF23-related hypophosphatemia include X-linked hypophosphatemia (XLH), autosomal dominant hypophosphatemic rickets, autosomal recessive hypophosphatemic rickets, fibrous dysplasia/McCune-Albright syndrome, and tumor-induced osteomalacia (TIO). Complications of conventional therapy with oral phosphate and vitamin D analogs comprise gastrointestinal distress, hypercalcemia, nephrocalcinosis, and secondary/tertiary hyperparathyroidism. In both children and adults with XLH and TIO, the anti-FGF23 antibody burosumab exhibits a favorable safety profile and is associated with healing of rickets in affected children and improvement of osteomalacia in both children and adults.

CONCLUSION

The treatment paradigm for XLH and TIO is changing based on data from recent clinical trials. Research suggest that burosumab is effective and safe for pediatric and adult patients with XLH or TIO.

Pituitary Tumors: Genetic and Molecular Factors Underlying Pathogenesis and Clinical Behavior

Pituitary neuroendocrine tumors (PitNETs) are the most common intracranial neoplasms. Although generally benign, they can show a clinically aggressive course, with local invasion, recurrences, and resistance to medical treatment. No universally accepted biomarkers of aggressiveness are available yet, and predicting clinical behavior of PitNETs remains a challenge. In rare cases, the presence of germline mutations in specific genes predisposes to PitNET formation, as part of syndromic diseases or familial isolated pituitary adenomas, and associates to more aggressive, invasive, and drug-resistant tumors. The vast majority of cases is represented by sporadic PitNETs. Somatic mutations in the α subunit of the stimulatory G protein gene (gsp) and in the ubiquitin-specific protease 8 (USP8) gene have been recognized as pathogenetic factors in sporadic GH- and ACTH-secreting PitNETs, respectively, without an association with a worse clinical phenotype. Other molecular factors have been found to significantly affect PitNET drug responsiveness and invasive behavior. These molecules are cytoskeleton and/or scaffold proteins whose alterations prevent proper functioning of the somatostatin and dopamine receptors, targets of medical therapy, or promote the ability of tumor cells to invade surrounding tissues. The aim of the present review is to provide an overview of the genetic and molecular alterations that can contribute to determine PitNET clinical behavior. Understanding subcellular mechanisms underlying pituitary tumorigenesis and PitNET clinical phenotype will hopefully lead to identification of new potential therapeutic targets and new markers predicting the behavior and the response to therapeutic treatments of PitNETs.

Fibrous and Fibro-Osseous Lesions of Bone

Fibrous and fibro-osseous tumors are some of the most common benign lesions involving bones. Although many of the histomorphologic features of these tumors overlap significantly, an interdisciplinary approach helps to consolidate the classification of these tumors. Herein, the clinical, radiologic, and pathologic features of lesions within these categories are described.

Somatic mutations of GNA11 and GNAQ in CTNNB1-mutant aldosterone-producing adenomas presenting in puberty, pregnancy or menopause

Most aldosterone-producing adenomas (APAs) have gain-of-function somatic mutations of ion channels or transporters. However, their frequency in aldosterone-producing cell clusters of normal adrenal gland suggests a requirement for codriver mutations in APAs. Here we identified gain-of-function mutations in both CTNNB1 and GNA11 by whole-exome sequencing of 3/41 APAs. Further sequencing of known CTNNB1-mutant APAs led to a total of 16 of 27 (59%) with a somatic p.Gln209His, p.Gln209Pro or p.Gln209Leu mutation of GNA11 or GNAQ. Solitary GNA11 mutations were found in hyperplastic zona glomerulosa adjacent to double-mutant APAs. Nine of ten patients in our UK/Irish cohort presented in puberty, pregnancy or menopause. Among multiple transcripts upregulated more than tenfold in double-mutant APAs was LHCGR, the receptor for luteinizing or pregnancy hormone (human chorionic gonadotropin). Transfections of adrenocortical cells demonstrated additive effects of GNA11 and CTNNB1 mutations on aldosterone secretion and expression of genes upregulated in double-mutant APAs. In adrenal cortex, GNA11/Q mutations appear clinically silent without a codriver mutation of CTNNB1.

68Ga-PSMA-HBED-CC PET/CT Findings in a Patient of Polyostotic Fibrous Dysplasia

ABSTRACT

A 43-year-old man diagnosed with fibrous dysplasia with McCune-Albright syndrome was subjected to 18F-fluoride bone scan and 68Ga-PSMA-HBED-CC PET/CT as per the institution protocol. 18F-bone scan revealed extensive involvement of axial and appendicular skeleton confirming polyostotic fibrous dysplasia. 68Ga-PSMA PET/CT showed increased tracer uptake in corresponding lesions of fibrous dysplasia. PSMA uptake in fibrous dysplasia lesions has been rarely described with literature evidence being limited to anecdotal case reports. Nevertheless, due to increasing use of PSMA PET/CT, one should be aware of this false-positive finding to avoid misinterpretation of the scans.

Maternal GNAS Contributes to the Extra-Large G Protein α-Subunit (XLαs) Expression in a Cell Type-Specific Manner

GNAS encodes the stimulatory G protein alpha-subunit (Gsα) and its large variant XLαs. Studies have suggested that XLαs is expressed exclusively paternally. Thus, XLαs deficiency is considered to be responsible for certain findings in patients with paternal GNAS mutations, such as pseudo-pseudohypoparathyroidism, and the phenotypes associated with maternal uniparental disomy of chromosome 20, which comprises GNAS. However, a study of bone marrow stromal cells (BMSC) suggested that XLαs could be biallelically expressed. Aberrant BMSC differentiation due to constitutively activating GNAS mutations affecting both Gsα and XLαs is the underlying pathology in fibrous dysplasia of bone. To investigate allelic XLαs expression, we employed next-generation sequencing and a polymorphism common to XLαs and Gsα, as well as A/B, another paternally expressed GNAS transcript. In mouse BMSCs, Gsα transcripts were 48.4 ± 0.3% paternal, while A/B was 99.8 ± 0.2% paternal. In contrast, XLαs expression varied among different samples, paternal contribution ranging from 43.0 to 99.9%. Sample-to-sample variation in paternal XLαs expression was also detected in bone (83.7-99.6%) and cerebellum (83.8 to 100%) but not in cultured calvarial osteoblasts (99.1 ± 0.1%). Osteoblastic differentiation of BMSCs shifted the paternal XLαs expression from 83.9 ± 1.5% at baseline to 97.2 ± 1.1%. In two human BMSC samples grown under osteoinductive conditions, XLαs expression was also predominantly monoallelic (91.3 or 99.6%). Thus, the maternal GNAS contributes significantly to XLαs expression in BMSCs but not osteoblasts. Altered XLαs activity may thus occur in certain cell types irrespective of the parental origin of a GNAS defect.

Genetics of Acromegaly and Gigantism

Growth hormone (GH)-secreting pituitary tumours represent the most genetically determined pituitary tumour type. This is true both for germline and somatic mutations. Germline mutations occur in several known genes (AIP, PRKAR1A, GPR101, GNAS, MEN1, CDKN1B, SDHx, MAX) as well as familial cases with currently unknown genes, while somatic mutations in GNAS are present in up to 40% of tumours. If the disease starts before the fusion of the epiphysis, then accelerated growth and increased final height, or gigantism, can develop, where a genetic background can be identified in half of the cases. Hereditary GH-secreting pituitary adenoma (PA) can manifest as isolated tumours, familial isolated pituitary adenoma (FIPA) including cases with AIP mutations or GPR101 duplications (X-linked acrogigantism, XLAG) or can be a part of systemic diseases like multiple endocrine neoplasia type 1 or type 4, McCune-Albright syndrome, Carney complex or phaeochromocytoma/paraganglioma-pituitary adenoma association. Family history and a search for associated syndromic manifestations can help to draw attention to genetic causes; many of these are now tested as part of gene panels. Identifying genetic mutations allows appropriate screening of associated comorbidities as well as finding affected family members before the clinical manifestation of the disease. This review focuses on germline and somatic mutations predisposing to acromegaly and gigantism.

First radiobiological characterization of the McCune-Albright syndrome: influence of the ATM protein and effect of statins + bisphosphonates treatment

PURPOSE

MacCune-Albright syndrome (MAS) is a rare autosomal dominant osteo-hormonal disorder. MAS is characterized by a severe form of polyostotic fibrous dysplasia, 'café-au-lait' pigmentation of the skin and multiple endocrinopathies. MAS was shown to be caused by mosaic missense somatic mutations in the GNAS gene coding for the alpha-subunit of the stimulatory G-protein. MAS is also associated with radiation-induced malignant tumors, like osteosarcoma, fibrosarcoma and chondrosarcoma but their origin remains misunderstood. In parallel, bisphosphonates treatment was shown to improve the MAS patients' outcome, notably by increasing bone density but, again, the molecular mechanisms supporting these observations remain misunderstood.

MATERIALS AND METHODS

Here, by using fibroblast and osteoblast cell lines derived from 2 MAS patients, the major radiobiological features of MAS were investigated. Notably, the clonogenic cell survival, the micronuclei and the γH2AX, pATM and MRE11 immunofluorescence assays were applied to MAS cells.

RESULTS

It appears that cells from the 2 MAS patients are associated with a moderate but significant radiosensitivity, a delayed radiation-induced nucleoshuttling of the ATM kinase likely caused by its sequestration in cytoplasm, suggesting impaired DNA double-strand breaks (DSB) repair and signaling in both fibroblasts and osteoblasts. Such delay may be partially corrected by using bisphosphonates combined with statins, which renders cells more radioresistant.

CONCLUSIONS

Our findings represent the first radiobiological characterization of fibroblasts and osteoblasts providing from MAS patients. Although the number of studied cases is reduced, our findings suggest that the MAS cells tested belong to the group of syndromes associated with moderate but significant radiosensitivity. Further investigations are however required to secure the clinical transfer of the combination of bisphosphonates and statins, to reduce the disease progression and to better evaluate the potential risks linked to radiation exposure.

Fibrous Dysplasia of the Spine-A Case Involving the Polyostotic Form Isolated to the Thoracolumbar Spine

Fibrous dysplasia of the spine in a polyostotic form is very rare, with fewer than 36 cases discussed in the literature and there is no such case in Indonesia that has been reported. The aim of this report is to present a case from Indonesia of polyostotic fibrous dysplasia isolated in the spine. We report a case of a 38-year-old Sundanese man with a 1-year history of progressive back pain and weakness of both lower extremities. There was no history leading to infection and no previous trauma. A physical examination revealed kyphoscoliotic deformity, a café au lait spot, tenderness at the thoracolumbar region, and neurological deficits. Laboratory studies were within normal ranges. Plain radiographs showed lytic lesion and kyphoscoliosis. Magnetic resonance imaging showed an endosteal scalloping, infiltrative process, expansion, and destruction in the vertebral bodies from T2 to L5. The findings of an aggressive destructive process was highly suspicious of a malignant process, relying on differential diagnosis and metastases, plasma cell myeloma, bone tumor and chronic infectious spondylitis. Histology revealed an irregularly oriented osteoid without osteoblastic rimming but surrounded by fibroblastic proliferation with a C-shaped sign. Investigations revealed a diagnosis of polyostotic fibrous dysplasia of the thoracolumbar spine in isolation. The patient underwent T5-S1 stabilization and bone grafting. At 1 year postoperative, the patient was asymptomatic; there was no recurrence and minimal neurological deficit with grade II on the modified McCormick scale. A case of the polyostotic form of fibrous dysplasia of the spine in isolation has never been reported in Indonesia. The extreme rarity of this type of presentation can pose a diagnostic dilemma, and in cases isolated to the spine, surgical treatment with posterior stabilization, decompression, and bone grafting gives a good functional outcome.

[Fibrous dysplasia]

Fibrous dysplasia is a benign intraosseous tumor, which can occur as a monostotic or polyostotic disease. As a combination of dermatological and endocrinological features it is known as McCune-Albright syndrome, in conjunction with intramuscular myxoma as Mazabraud's syndrome. Fibrous dysplasia originates from a genetic defect, a postzygotic mutation of the GNAS gene, leading to incorrect regulation of the osteogenesis of the affected area of the bone. The weakening of the bone causes a variety of symptoms ranging from isolated local pain, acute fractures up to severe deformation of the bones. In the latter case the patients may lose the capability of walking. The orthopedic treatment provides suitable methods to set and stabilize fractures, to strengthen weakened bones and to straighten out and stabilize deformed long bones. This can help many patients return to a high level of pain-free mobility and even allow the most badly affected patients to lead a better life with a restricted mobility.

RANKL Inhibition in Fibrous Dysplasia of Bone: A Preclinical Study in a Mouse Model of the Human Disease

Fibrous dysplasia of bone/McCune-Albright syndrome (Polyostotic FD/MAS; OMIM#174800) is a crippling skeletal disease caused by gain-of-function mutations of G_s α. Enhanced bone resorption is a recurrent histological feature of FD and a major cause of fragility of affected bones. Previous work suggests that increased bone resorption in FD is driven by RANKL and some studies have shown that the anti-RANKL monoclonal antibody, denosumab, reduces bone turnover and bone pain in FD patients. However, the effect of RANKL inhibition on the histopathology of FD and its impact on the natural history of the disease remain to be assessed. In this study, we treated the EF1α-G_s α^R201C mice, which develop an FD-like phenotype, with an anti-mouse RANKL monoclonal antibody. We found that the treatment induced marked radiographic and microscopic changes at affected skeletal sites in 2-month-old mice. The involved skeletal segments became sclerotic due to the deposition of new, highly mineralized bone within developing FD lesions and showed a higher mechanical resistance compared to affected segments from untreated transgenic mice. Similar changes were also detected in older mice with a full-blown skeletal phenotype. The administration of anti-mouse RANKL antibody arrested the growth of established lesions and, in young mice, prevented the appearance of new ones. However, after drug withdrawal, the newly formed bone was remodelled into FD tissue and the disease progression resumed in young mice. Taken together, our results show that the anti-RANKL antibody significantly affected the bone pathology and natural history of FD in the mouse. Pending further work on the prevention and management of relapse after treatment discontinuation, our preclinical study suggests that RANKL inhibition may be an effective therapeutic option for FD patients. © 2019 American Society for Bone and Mineral Research.

Locally aggressive monostotic fibrous dysplasia of the cervical spine mimicking malignancy: a case report and literature review

We report the case of a 30-year-old woman with histologically proven monostotic fibrous dysplasia of C2 revealed by a pathological fracture of the odontoid process. Radiological investigations showed a ground-glass mineralization of the vertebral body, a centimetric lytic area with poorly defined margins involving the inferior part of the vertebral body and inferior endplate and a fracture through an osteolytic area in the base of the odontoid process. Owing to the vertebral instability, a surgical procedure combining C0-C5 fixation and posterior bone grafting was performed. The surgical biopsy was inconclusive and pathological confirmation was finally obtained through a percutaneous needle biopsy under fluoroscopic guidance. At 26-month follow-up, the patient still experienced mild persistent cervical posterior neck pain and stiffness possibly related to a C5-6 laxity below the intervertebral fixation. This case combines three radiological findings, which are unusual in fibrous dysplasia: monostotic presentation involving the spine, some aggressive radiographic features, and a pathological fracture.

Improved Molecular Diagnosis of McCune-Albright Syndrome and Bone Fibrous Dysplasia by Digital PCR

McCune-Albright syndrome (MAS) is a rare congenital disorder characterized by the association of endocrine and nonendocrine anomalies caused by somatic activating variants of GNAS. The mosaic state of variants makes the clinical presentation extremely heterogeneous depending on involved tissues. Biological samples bearing a low level of mosaicism frequently lead to false-negative results with an underestimation of causative molecular alterations, and the analysis of biopsies is often needed to obtain a molecular diagnosis. To date, no reliable analytical method for the noninvasive testing of blood is available. This study was aimed at validating a novel and highly sensitive technique, the digital PCR (dPCR), to increase the detection rate of GNAS alterations in patients with a clinical suspicion of MAS and, in particular, in blood. We screened different tissues (blood, bone, cutis, ovary, and ovarian cyst) collected from 54 MAS patients by different technical approaches. Considering blood, Sanger was unable to detect mutations, the allele-specific PCR and the co-amplification at lower denaturation temperature had a 9.1% and 18.1% detection rate, respectively, whereas the dPCR reached a 37.8% detection rate. In conclusion, the dPCR resulted in a cost-effective, reliable, and rapid method allowing the selective amplification of low-frequency variants and able to improve GNAS mutant allele detection, especially in the blood.

Mandibular 3-dimensional finite element analysis for a patient with an aggressive form of craniofacial fibrous dysplasia

The longitudinal change in mandibular volume and configuration was quantitatively evaluated in a patient with craniofacial fibrous dysplasia (FD). The influence of mechanical stress on the enlargement that is characteristic of FD was verified via finite element analysis (FEA). The patient was a 38-year-old man diagnosed with craniofacial FD in the mandible. He underwent surgical reduction of FD, but the lesion continued to grow and caused facial asymmetry and masticatory disturbance because of missing teeth. An occlusal overlay removable partial denture was constructed for his lower jaw. Computed tomography (CT) images were acquired 4 times in 10 years, and 3-dimensional (3-D) models were reconstructed from these data. The 3-D models were analyzed volumetrically and morphologically and used for FEA. The FD lesion in the mandible enlarged nonuniformly and had site specificity. From the results of FEA, it is suggested that compression stress induced by the occlusal force through the denture may have influenced the direction of enlargement in FD.

Regulation of fibroblast growth factor 23 (FGF23) in health and disease

Fibroblast growth factor 23 (FGF23) is mainly produced in the bone and, upon secretion, forms a complex with a FGF receptor and coreceptor αKlotho. FGF23 can exert several endocrine functions, such as inhibiting renal phosphate reabsorption and 1,25-dihydroxyvitamin D3 production. Moreover, it has paracrine activities on several cell types, including neutrophils and hepatocytes. Klotho and Fgf23 deficiencies result in pathologies otherwise encountered in age-associated diseases, mainly as a result of hyperphosphataemia-dependent calcification. FGF23 levels are also perturbed in the plasma of patients with several disorders, including kidney or cardiovascular diseases. Here, we review mechanisms controlling FGF23 production and discuss how FGF23 regulation is perturbed in disease.

Congenital eye anomalies: More mosaic than thought?

The eye is a sensory organ that primarily captures light and provides the sense of sight, as well as delivering non-visual light information involving biological rhythms and neurophysiological activities to the brain. Since the early 1990s, rapid advances in molecular biology have enabled the identification of developmental genes, genes responsible for human congenital diseases, and relevant genes of mutant animals with various anomalies. In this review, we first look at the development of the eye, and we highlight seminal reports regarding archetypal gene defects underlying three developmental ocular disorders in humans: (1) holoprosencephaly (HPE), with cyclopia being exhibited in the most severe cases; (2) microphthalmia, anophthalmia, and coloboma (MAC) phenotypes; and (3) anterior segment dysgenesis (ASDG), known as Peters anomaly and its related disorders. The recently developed methods, such as next-generation sequencing and genome editing techniques, have aided the discovery of gene mutations in congenital eye diseases and gene functions in normal eye development. Finally, we discuss Pax6-genome edited mosaic eyes and propose that somatic mosaicism in developmental gene mutations should be considered a causal factor for variable phenotypes, sporadic cases, and de novo mutations in human developmental disorders.

Identification of novel GNAS mutations in intramuscular myxoma using next-generation sequencing with single-molecule tagged molecular inversion probes

Background

Intramuscular myxoma (IM) is a hypocellular benign soft tissue neoplasm characterized by abundant myxoid stroma and occasional hypercellular areas. These tumors can, especially on biopsy material, be difficult to distinguish from low-grade fibromyxoid sarcoma or low-grade myxofibrosarcoma. GNAS mutations are frequently involved in IM, in contrast to these other malignant tumors. Therefore, sensitive molecular techniques for detection of GNAS aberrations in IM, which frequently yield low amounts of DNA due to poor cellularity, will be beneficial for differential diagnosis.

Methods

In our study, a total of 34 IM samples from 33 patients were analyzed for the presence of GNAS mutations, of which 29 samples were analyzed using a gene-specific TaqMan genotyping assay for the detection of GNAS hotspot mutations c.601C > T and c602G > A in IM, and 32 samples using a novel next generation sequencing (NGS)-based approach employing single-molecule tagged molecular inversion probes (smMIP) to identify mutations in exon 8 and 9 of GNAS. Results between the two assays were compared for their ability to detect GNAS mutations with high confidence.

Results

In total, 23 of 34 samples were successfully analyzed with both techniques showing GNAS mutations in 12 out of 23 (52%) samples. The remaining 11 samples were analyzed with either TaqMan assay or smMIP assay only. The TaqMan assay revealed GNAS mutations in 16 out of 29 samples (55%), with six samples c.601C > T (p.R201C; 38%) and ten samples c.602G > A (p.R201H; 62%) missense mutations. The smMIP assay identified mutations in 16 out of 28 samples (57%), with five samples c.601C > T (p.R201C; 31%) and seven samples c.602G > A (p.R201H; 44%) missense mutations. In addition, four samples (25%) revealed novel IM-associated mutations, including c.601C > A (p.R201S), c.602G > T (p.R201L), c.602G > C (p.R201P) and c.680A > G (p.Q227R). Combining the results of both tests, 23 out of 34 sporadic IM samples (68%) showed a GNAS mutation.

Conclusions

Both the TaqMan and the smMIP assay a show a high degree of concordance in detecting GNAS hotspot mutations in IM with comparable sensitivity. However, since the NGS-based smMIP assay permits mutation detection in whole exons of GNAS, a broader range of GNAS mutations can be identified by the smMIP approach.

Treatment of diaphyseal pathological fractures in children with monostotic fibrous dysplasia using cortical strut allografts and internal plating: A retrospective clinical study

Children with fibrous dysplasia (FD) chronically suffer from pain, pathological fractures, and limb deformities. The most effective methods for managing the associated pathological fractures remain controversial. The purpose of this study was to evaluate the clinical results of the treatment of diaphyseal pathological fractures in children with monostotic fibrous dysplasia (MFD) using cortical strut allografts and internal plating.We retrospectively analyzed outcomes in nine children (5 boys, 4 girls) with diaphyseal pathological fractures due to MFD, who were treated with cortical strut allografts and internal plating (6 femoral fractures and 3 humeral fractures) between July 2007 and November 2012. The median age of patients in our study was 10 years (range 6-14 years). The fracture healing time, pain, extremity function, refracture, graft resorption, and complications were recorded to evaluate treatment effects.The median time of follow-up was 69 months (range 60-75 months). All patients had good postoperative fracture healing with a median healing time of 14 weeks (range 12-16 weeks). None experienced refracture, graft resorption, nerve injury, or limitation of extremity function or other complications. The fixation remained stable in all patients, with no evidence of loosening screws after surgery.In pediatric patients, the described surgical approach is an effective and reliable treatment method for diaphyseal pathological fractures caused by MFD. Cortical strut allografts, which act as biological bone plates, can provide good mechanical support while increasing the rate of fracture union.

Using Digital Droplet Polymerase Chain Reaction to Detect the Mosaic GNAS Mutations in Whole Blood DNA or Circulating Cell-Free DNA in Fibrous Dysplasia and McCune-Albright Syndrome

The GNAS postzygotic mosaic activating mutations involved in fibrous dysplasia and McCune-Albright syndrome (MAS) are not detectable in leukocytes by Sanger sequencing. Digital droplet polymerase chain reaction detects GNAS mutations in 7 of 12 patients (58.3%) suspected to have fibrous dysplasia/MAS from whole blood DNA, and in 4 of 5 patients (80%) from circulating cell-free DNA.

Neonatal McCune-Albright Syndrome: A Unique Syndromic Profile With an Unfavorable Outcome

Somatic gain‐of‐function mutations of GNAS cause a spectrum of clinical phenotypes, ranging from McCune‐Albright syndrome (MAS) to isolated disease of bone, endocrine glands, and more rarely, other organs. In MAS, a syndrome classically characterized by polyostotic fibrous dysplasia (FD), café‐au‐lait (CAL) skin spots, and precocious puberty, the heterogenity of organ involvement, age of onset, and clinical severity of the disease are thought to reflect the variable size and the random distribution of the mutated cell clone arising from the postzygotic mutation. We report a case of neonatal MAS with hypercortisolism and cholestatic hepatobiliary dysfunction in which bone changes indirectly emanating from the disease genotype, and distinct from FD, led to a fatal outcome. Pulmonary embolism of marrow and bone fragments secondary to rib fractures was the immediate cause of death. Ribs, and all other skeletal segments, were free of changes of typical FD and fractures appeared to be the result of a mild‐to‐moderate degree of osteopenia. The mutated allele was abundant in the adrenal glands and liver, but not in skin, muscle, and fractured ribs, where it could only be demonstrated using a much more sensitive PNA hybridization probe‐based FRET (Förster resonance energy transfer) technique. Histologically, bilateral adrenal hyperplasia and cholestatic disease matched the abundant disease genotype in the adrenals and liver. Based on this case and other sporadic reports, it appears that gain‐of‐function mutations of GNAS underlie a unique syndromic profile in neonates characterized by CAL skin spots, hypercortisolism, hyperthyroidism, hepatic and cardiac dysfunction, and an absence (or latency) of FD, often with a lethal outcome. Taken together, our and previous cases highlight the phenotypic severity and the diagnostic and therapeutic challenges of MAS in neonates. Furthermore, our case specifically points out how secondary bone changes, unrelated to the direct impact of the mutation, may contribute to the unfavorable outcome of very early‐onset MAS. © 2018 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Mutational analysis of high-grade spindle cell sarcoma of the femur in Mazabraud's syndrome

Mazabraud's syndrome is a rare disorder characterised by the association of fibrous dysplasia with intramuscular myxomas. We present a 36-year-old woman with right anterior knee pain and a buttock mass. Imaging showed aggressive bone destruction within an area of fibrous dysplasia in the right femur and a mass with myxoid signal characteristics in the right adductor region. Biopsy of the femur revealed both fibrous dysplasia and a high-grade spindle cell sarcoma. Biopsy of the adductor mass confirmed a soft-tissue myxoma. Molecular genetic analysis revealed an identical R201H substitution in the GNAS1 gene in the sarcoma, the myxoma, and also the conventional fibrous dysplasia.

Gαs signaling in skeletal development, homeostasis and diseases

Skeletal development is exquisitely controlled both spatially and temporally by cell signaling networks. Gα_s is the stimulatory α-subunit in a heterotrimeric G protein complex transducing the signaling of G-protein-coupled receptors (GPCRs), responsible for controlling both skeletal development and homeostasis. Gα_s, encoded by the GNAS gene in humans, plays critical roles in skeletal development and homeostasis by regulating commitment, differentiation and maturation of skeletal cells. Gα_s-mediated signaling interacts with the Wnt and Hedgehog signaling pathways, both crucial regulators of skeletal development, remodeling and injury repair. Genetic mutations that disrupt Gα_s functions cause human disorders with severe skeletal defects, such as fibrous dysplasia of bone and heterotopic bone formation. This chapter focuses on the crucial roles of Gα_s signaling during skeletal development and homeostasis, and the pathological mechanisms underlying skeletal diseases caused by GNAS mutations.

The causes and consequences of pituitary gigantism

In the general population, height is determined by a complex interplay between genetic and environmental factors. Pituitary gigantism is a rare but very important subgroup of patients with excessive height, as it has an identifiable and clinically treatable cause. The disease is caused by chronic growth hormone and insulin-like growth factor 1 secretion from a pituitary somatotrope adenoma that forms before the closure of the epiphyses. If not controlled effectively, this hormonal hypersecretion could lead to extremely elevated final adult height. The past 10 years have seen marked advances in the understanding of pituitary gigantism, including the identification of genetic causes in ~50% of cases, such as mutations in the AIP gene or chromosome Xq26.3 duplications in X-linked acrogigantism syndrome. Pituitary gigantism has a male preponderance, and patients usually have large pituitary adenomas. The large tumour size, together with the young age of patients and frequent resistance to medical therapy, makes the management of pituitary gigantism complex. Early diagnosis and rapid referral for effective therapy appear to improve outcomes in patients with pituitary gigantism; therefore, a high level of clinical suspicion and efficient use of diagnostic resources is key to controlling overgrowth and preventing patients from reaching very elevated final adult heights.

First two cases of craniomaxillofacial fibrous dysplasia from Nepal - case series

Fibrous dysplasia is a benign fibro-osseous disease of the bone, which is most commonly associated with congenital mutations in cAMP regulating protein Gsα coded by GNAS-1 gene. Often it is seen involving the craniofacial skeleton and can range from an asymptomatic monostotic form to polyostotic variant involving almost all the bones of the skull, thereby leading to functional and esthetic problems. This requires a continuous monitoring of the involved region throughout the life of the patient, even after the surgical interventions. We are presenting two cases of craniofacial form of fibrous dysplasia. One case shows monostotic form, while the other case shows features of polyostotic form of disease. To the best of our knowledge, these are the first two cases of craniomaxillofacial fibrous dysplasia from Nepal, which will be reported and published.

Fibrous dysplasia of the jaws: Integrating molecular pathogenesis with clinical, radiological, and histopathological features

Fibrous dysplasia is a non-neoplastic developmental process that affects the craniofacial bones, characterized by painless enlargement as a result of bone substitution by abnormal fibrous tissue. Postzygotic somatic activating mutations in the GNAS1 gene cause fibrous dysplasia and have been extensively investigated, as well as being helpful in the differential diagnosis of the disease. Fibrous dysplasia may involve one (monostotic) or multiple bones (polyostotic), sporadically or in association with McCune-Albright syndrome, Jeffe-Lichenstein syndrome, or Mazabreud syndrome. This review summarizes the current knowledge on fibrous dysplasia, emphasizing the value of integrating the understanding of its molecular pathogenesis with the clinical, radiological, and histopathological features. In addition, we address important aspects related to the differential diagnosis and patient management.

HDAC8, A Potential Therapeutic Target, Regulates Proliferation and Differentiation of Bone Marrow Stromal Cells in Fibrous Dysplasia

Fibrous dysplasia (FD) is a disease of postnatal skeletal stem cells caused by activating mutations of guanine nucleotide-binding protein alpha-stimulating activity polypeptide (GNAS). FD is characterized by high proliferation and osteogenesis disorder of bone marrow stromal cells (BMSCs), resulting in bone pain, deformities, and fractures. The cAMP-CREB pathway, which is activated by GNAS mutations, is known to be closely associated with the occurrence of FD. However, so far there is no available targeted therapeutic strategy for FD, as a critical issue that remains largely unknown is how this pathway is involved in FD. Our previous study revealed that histone deacetylase 8 (HDAC8) inhibited the osteogenic differentiation of BMSCs via epigenetic regulation. Here, compared with normal BMSCs, FD BMSCs exhibited significantly high proliferation and weak osteogenic capacity in response to HDAC8 upregulation and tumor protein 53 (TP53) downregulation. Moreover, inhibition of cAMP reduced HDAC8 expression, increased TP53 expression and resulted in the improvement of FD phenotype. Importantly, HDAC8 inhibition prevented cAMP-induced cell phenotype and promoted osteogenesis in nude mice that were implanted with FD BMSCs. Mechanistically, HDAC8 was identified as a transcriptional target gene of CREB1 and its transcription was directly activated by CREB1 in FD BMSCs. In summary, our study reveals that HDAC8 associates with FD phenotype and demonstrates the mechanisms regulated by cAMP-CREB1-HDAC8 pathway. These results provide insights into the molecular regulation of FD pathogenesis, and offer novel clues that small molecule inhibitors targeting HDAC8 are promising clinical treatment for FD. Stem Cells Translational Medicine 2019;8:148&14.

PIK3CA-associated developmental disorders exhibit distinct classes of mutations with variable expression and tissue distribution

Mosaicism is increasingly recognized as a cause of developmental disorders with the advent of next-generation sequencing (NGS). Mosaic mutations of PIK3CA have been associated with the widest spectrum of phenotypes associated with overgrowth and vascular malformations. We performed targeted NGS using 2 independent deep-coverage methods that utilize molecular inversion probes and amplicon sequencing in a cohort of 241 samples from 181 individuals with brain and/or body overgrowth. We identified PIK3CA mutations in 60 individuals. Several other individuals (n = 12) were identified separately to have mutations in PIK3CA by clinical targeted-panel testing (n = 6), whole-exome sequencing (n = 5), or Sanger sequencing (n = 1). Based on the clinical and molecular features, this cohort segregated into three distinct groups: (a) severe focal overgrowth due to low-level but highly activating (hotspot) mutations, (b) predominantly brain overgrowth and less severe somatic overgrowth due to less-activating mutations, and (c) intermediate phenotypes (capillary malformations with overgrowth) with intermediately activating mutations. Sixteen of 29 PIK3CA mutations were novel. We also identified constitutional PIK3CA mutations in 10 patients. Our molecular data, combined with review of the literature, show that PIK3CA-related overgrowth disorders comprise a discontinuous spectrum of disorders that correlate with the severity and distribution of mutations.

The clinical and molecular spectrum of PIK3CA-related developmental disorders are correlated with types of mutations, tissue distributions, and levels of mosaicism with the clinical phenotype.

Scoliosis in Fibrous Dysplasia/McCune-Albright Syndrome: Factors Associated With Curve Progression and Effects of Bisphosphonates

Scoliosis is a complication of fibrous dysplasia/McCune-Albright syndrome (FD/MAS); however, risk factors and long-term outcomes are unknown. Bisphosphonates are commonly used; however, it is unknown whether their use decrease the risk of progressive scoliosis. Clinical data from the National Institutes of Health (NIH) cohort study was reviewed. Cobb angles were measured, and variables associated with scoliosis progression were identified. Of 138 subjects with available radiographs, 84 (61%) had scoliosis, including 55 (65%) classified as mild (Cobb angle >10 to ≤30 degrees), 11 (13%) as moderate (>30 to ≤45 degrees), and 18 (22%) as severe (>45 degrees). Total skeletal disease burden was highly associated with scoliosis severity (p < 0.0001). Endocrinopathies associated with scoliosis included fibroblast growth factor 23 (FGF23)-mediated hypophosphatemia (p < 0.001) and hyperthyroidism (p < 0.001). Bone turnover markers, including osteocalcin and NTX-telopeptides, were associated with severe scoliosis (p < 0.01). Associations were identified between Cobb angle and functional metrics, including leg length discrepancy (p < 0.01), hip range of motion (p < 0.05), and strength of the gluteus medius and maximus (p < 0.01). Longitudinal analyses were conducted in 69 subjects who had serial radiographs over a median 4.9-year period (range, 0.9 to 14.7 years). Twenty-two subjects were treated with bisphosphonates; there was no difference in Cobb angle progression compared to untreated subjects (0.10 versus 0.53 degrees/year, p = 0.36). Longitudinal data was available for 10 of 12 subjects treated with spinal fusion; one had instrumentation failure, but in nine subjects Cobb angles were stable with 6.1 years of follow-up (range, 0.9 to 14.7 years). Two fatalities from scoliosis-associated restrictive lung disease occurred in subjects managed non-operatively. Scoliosis occurs frequently in patients with polyostotic FD, and may be potentially fatal. The primary risk factor for progressive scoliosis is total skeletal disease burden. Treatable features that contribute to scoliosis progression include leg length discrepancy, FGF23-mediated hypophosphatemia, and hyperthyroidism. Current data do not support routine use of bisphosphonates to prevent progression of spinal curvature. Spinal fusion is frequently effective in providing long-term stability, and may be lifesaving. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Growth hormone-Insulin-like growth factor 1 axis hyperactivity on bone fibrous dysplasia in McCune-Albright Syndrome

CONTEXT

In fibrous dysplasia (BFD), normal bone and bone marrow are replaced by fibro-osseous tissue, leading to fracture, deformity and pain. BFD may be isolated, or in association with cutaneous hyperpigmentation and/or hyperfunctioning endocrinopathies, termed McCune-Albright syndrome (MAS). GH hypersecretion has been described in 10%-20% of MAS-BFD patients. Aim of the study was to determine the impact of GH-insulin like growth factor 1 (IGF1) axis hyperactivity on MAS-BFD morbidities and the efficacy of GH excess therapy.

DESIGN AND PATIENTS

A multicentric cross-sectional analysis was conducted on three different MAS cohorts. From 195 MAS patients, 37 subjects (19%) with GH excess were identified and compared with 34 MAS controls without GH hypersecretion.

RESULTS

Mean head circumference SDS was significantly higher in GH excess: 4.025 SDS vs 0.683 SDS (P < .0001). The risk of optic neuropathy (Odds ratio 4.231; P = .039), hearing deficit (Odds ratio 2.961; P = .0481), facial asymmetry (Odds ratio 6.563; P = .0192), malignancies (Odds ratio 15.24; P = .0173) were higher in GH excess group. Overall, pharmacotherapy (octreotide alone 10-30 mg/mo or with pegvisomant 10-20 mg/d) was effective in IGF1 normalization (IGF1 Z-score between -2 and +2 SDS) in 21/29 patients (72.4%) with good compliance to the regimen. Late diagnosis and GH excess treatment after 16 years old of age was associated with an increased risk of optic neuropathy (Odds ratio 4.500; P = .0491) and growth of pituitary adenomas (Odds ratio 7.846; P = .050).

CONCLUSIONS

GH-IGF1 hyperactivity increases risk of morbidities in MAS. Medical therapy is effective in normalizing IGF1 in most patients, and early treatment during paediatric age is associated with a decreased risk of optic neuropathy and GH-secreting adenomas growth.

Constitutive stimulatory G protein activity in limb mesenchyme impairs bone growth

GNAS mutations leading to constitutively active stimulatory G protein alpha-subunit (Gsα) cause different tumors, fibrous dysplasia of bone, and McCune-Albright syndrome, which are typically not associated with short stature. Enhanced signaling of the parathyroid hormone/parathyroid hormone-related peptide receptor, which couples to multiple G proteins including Gsα, leads to short bones with delayed endochondral ossification. It has remained unknown whether constitutive Gsα activity also impairs bone growth. Here we generated mice expressing a constitutively active Gsα mutant (Gsα-R201H) conditionally upon Cre recombinase (cGsα^R201H mice). Gsα-R201H was expressed in cultured bone marrow stromal cells from cGsα^R201H mice upon adenoviral-Cre transduction. When crossed with mice in which Cre is expressed in a tamoxifen-regulatable fashion (CAGGCre-ER™), tamoxifen injection resulted in mosaic expression of the transgene in double mutant offspring. We then crossed the cGsα^R201H mice with Prx1-Cre mice, in which Cre is expressed in early limb-bud mesenchyme. The double mutant offspring displayed short limbs at birth, with narrow hypertrophic chondrocyte zones in growth plates and delayed formation of secondary ossification center. Consistent with enhanced Gsα signaling, bone marrow stromal cells from these mice demonstrated increased levels of c-fos mRNA. Our findings indicate that constitutive Gsα activity during limb development disrupts endochondral ossification and bone growth. Given that Gsα haploinsufficiency also leads to short bones, as in patients with Albright's hereditary osteodystrophy, these results suggest that a tight control of Gsα activity is essential for normal growth plate physiology.

Combining Real-Time COLD- and MAMA-PCR TaqMan Techniques to Detect and Quantify R201 GNAS Mutations in the McCune-Albright Syndrome

BACKGROUND/AIM

The McCune-Albright syndrome (MAS) is a potentially severe disorder hallmarked by fibrous bone dysplasia, café-au-lait skin spots, and endocrine hyperfunction. It is caused by postzygotic activating mutations at the R201 codon of the GNAS gene, leading to a state of somatic mosaicism. Our aim was to improve the mutation detection rate and to quantify the presence of R201 GNAS mutations in different DNA samples from MAS patients.

METHODS

Real-time COLD- and MAMA-PCR TaqMan techniques were combined to search for R201 mutations in the DNA of blood or affected tissues from 16 previously molecularly characterized MAS patients, from a further 84 subjects with MAS signs who were R201 negative at RFLP analysis, and from 36 controls. The ability of this new method to provide quantitative data was tested in the serial dilution of wild-type, R201H, or R201C cloned plasmid DNA samples; the mutant abundance was measured by spectrophotometry.

RESULTS

A linear correlation between the true and the relative mutant abundance was observed until 2.5%, indicating a reliable quantification of R201 mutations. The assay's sensitivity was 0.05%, similar to that of previously described molecular methods.

CONCLUSION

The real-time COLD-MAMA-PCR approach is a rapid, efficient, and inexpensive molecular technique for the identification of mutant alleles poorly represented in DNA samples.
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Genetic Causes of Rickets

Rickets is a metabolic bone disease that develops as a result of inadequate mineralization of growing bone due to disruption of calcium, phosphorus and/or vitamin D metabolism. Nutritional rickets remains a significant child health problem in developing countries. In addition, several rare genetic causes of rickets have also been described, which can be divided into two groups. The first group consists of genetic disorders of vitamin D biosynthesis and action, such as vitamin D-dependent rickets type 1A (VDDR1A), vitamin D-dependent rickets type 1B (VDDR1B), vitamin D-dependent rickets type 2A (VDDR2A), and vitamin D-dependent rickets type 2B (VDDR2B). The second group involves genetic disorders of excessive renal phosphate loss (hereditary hypophosphatemic rickets) due to impairment in renal tubular phosphate reabsorption as a result of FGF23-related or FGF23-independent causes. In this review, we focus on clinical, laboratory and genetic characteristics of various types of hereditary rickets as well as differential diagnosis and treatment approaches.

Induced GnasR201H expression from the endogenous Gnas locus causes fibrous dysplasia by up-regulating Wnt/β-catenin signaling

Fibrous dysplasia (FD; Online Mendelian Inheritance in Man no. 174800) is a crippling skeletal disease caused by activating mutations of the GNAS gene, which encodes the stimulatory G protein Gα_s FD can lead to severe adverse conditions such as bone deformity, fracture, and severe pain, leading to functional impairment and wheelchair confinement. So far there is no cure, as the underlying molecular and cellular mechanisms remain largely unknown and the lack of appropriate animal models has severely hampered FD research. Here we have investigated the cellular and molecular mechanisms underlying FD and tested its potential treatment by establishing a mouse model in which the human FD mutation (R201H) has been conditionally knocked into the corresponding mouse Gnas locus. We found that the germ-line FD mutant was embryonic lethal, and Cre-induced Gnas FD mutant expression in early osteochondral progenitors, osteoblast cells, or bone marrow stromal cells (BMSCs) recapitulated FD features. In addition, mosaic expression of FD mutant Gα_s in BMSCs induced bone marrow fibrosis both cell autonomously and non-cell autonomously. Furthermore, Wnt/β-catenin signaling was up-regulated in FD mutant mouse bone and BMSCs undergoing osteogenic differentiation, as we have found in FD human tissue previously. Reduction of Wnt/β-catenin signaling by removing one Lrp6 copy in an FD mutant line significantly rescued the phenotypes. We demonstrate that induced expression of the FD Gα_s mutant from the mouse endogenous Gnas locus exhibits human FD phenotypes in vivo, and that inhibitors of Wnt/β-catenin signaling may be repurposed for treating FD and other bone diseases caused by Gα_s activation.

Detection of Rare Somatic GNAS Mutation in McCune-Albright Syndrome Using a Novel Peptide Nucleic Acid Probe in a Single Tube

McCune-Albright syndrome (MAS) is characterized by the triad of precocious puberty, café au lait pigmentation, and polyostotic fibrous dysplasia (FD) of bone, and is caused by post-zygotic somatic mutations-R201H or R201C-in the guanine nucleotide binding protein, alpha stimulating (GNAS) gene. In the present study, a novel peptide nucleic acid (PNA) probe with fluorescent labeling was designed to detect trace amounts of somatic mutant GNAS in a single tube reaction. The method was applied to screen GNAS mutations in six patients with MAS/FD. The results showed that the PNA probe assay could detect low abundant mutants in 200-fold excess of wild-type alleles. The GNAS mutation was found in three patients with severe disease (MAS) by using the assay. The other three patients with mild disease (having only FD) showed a wild-type result. This study has provided a simple method to detect trace amounts of GNAS mutants with high sensitivity in large amounts of wild-type DNA.

Bisphosphonate-induced zebra lines in fibrous dysplasia of bone: histo-radiographic correlation in a case of McCune-Albright syndrome

Bisphosphonates (BPs) are currently used in the treatment of diverse bone diseases including fibrous dysplasia of bone (FD). In pediatric patients, a radiographic consequence of cyclical administration of BPs is the development of apo-, epi-, and meta-physeal sclerotic bands, otherwise known as zebra lines, which result from the temporary inhibition of osteoclastic activity at the time of drug treatment. We report here on a child with McCune-Albright syndrome (FD in addition to hyperfunctioning endocrinopathies and skin hyperpigmentation) treated with cyclical intravenous infusions of pamidronate in which conventional radiography, contact microradiography, histology, and backscattered electron image analysis demonstrated that zebra lines formed only where bone was normal, were arrested at the boundary between FD-unaffected and FD-affected bone where bone is sclerotic, and were absent within the undermineralized FD bone. Moreover, in spite of the treatment, the FD lesions continued to expand. This case report is unique because no previously published studies correlated the radiographic and the histologic features of BP-induced zebra lines in the metaphysis of an FD-affected long bone of the limbs.

Craniofacial Fibrous Dysplasia of Zygomaticomaxillary Complex

Fibrous dysplasia is a benign bone disease first described by Lichtenstein in 1938. It is characterized by progressive replacement of normal bone with fibro-osseous connective tissue. When the disease involves craniofacial skeleton, it results in significant disfigurement and other functional problems. This paper reports a case of large craniofacial fibrous dysplasia involving zygomaticomaxillary complex in a 24-year old male patient. Clinical presentation and imaging characteristics of the pathology is discussed in detail. The disease caused significant facial asymmetry which was satisfactorily managed by surgical recontouring.

Relationship between GNAS1 T393C polymorphism and aseptic loosening after total hip arthroplasty

BACKGROUND

Aseptic loosening is a main cause for revision surgery after total hip arthroplasty (THA) and there is no reliable marker for the early detection of patients at high risk. This study has been performed to validate association of the T393C polymorphism (rs7121) in the GNAS1 gene, encoding for the alpha-subunit of heterotrimeric G-protein Gs, with risk for and time to aseptic loosening after THA, which has been demonstrated in our previous study.

METHODS

231 patients with primary THA and 234 patients suffering from aseptic loosening were genotyped for dependency on GNAS1 genotypes and analyzed.

RESULTS

Genotyping revealed almost similar minor allele frequencies of 0.49 and 0.46, respectively. Consistently, genotype distributions of both groups were not significantly different (p = 0.572). Neither gender nor GNAS1 genotype showed a statistically significant association with time to loosening (p = 0.501 and p = 0.840). Stratification by gender, as performed in our previous study, was not able to show a significant genotype-dependent difference in time (female p = 0.313; male p = 0.584) as well as median time to aseptic loosening (female p = 0.353; male p = 0.868).

CONCLUSION

This study was not able to confirm the results of our preliminary study. An association of the GNAS1 T393C polymorphisms with risk for and time to aseptic loosening after THA is unlikely.

Frequency of GNAS R201H substitution mutation in polyostotic fibrous dysplasia: Pyrosequencing analysis in tissue samples with or without decalcification

Guanine nucleotide-binding protein/α-subunit (GNAS) mutations are involved in fibrous dysplasia (FD) pathogenesis. Here, we analyzed GNAS mutations in FD which were performed by pyrosequencing DNA isolated from formalin-fixed paraffin-embedded (FFPE) tissue. The mutation detection rate was determined in FD specimens with and without decalcification. GNAS mutation was identified in 28 cases out of 87 FDs (32.18%) [p.R201C (N = 14) and p.R201H (N = 14)]. GNAS mutation was more likely to occur in polyostotic FD (7/28, 25.0%); FD without GNAS mutation was mostly monostotic form (56/59, 94.9%, P = 0.011). The G > A (R201H) mutation was more frequent in polyostotic FD (6/14 patients, 42.9%) than the C > T (R201C) mutation (1/14, 7.1%) (P = 0.077). We divided the FD cases into two subgroups: tissue specimens that were not decalcified (N = 35, 40.2%), and tissue specimens that were decalcified (N = 52, 59.8%). GNAS mutation was more frequently identified in FD specimens that were not subjected to decalcification (23/35, 65.7%) than in FD specimens that were decalcified (5/52, 9.6%) (P = 0.001). In conclusion, mutation analysis of GNAS by pyrosequencing has diagnostic value in FFPE tissue of patients with FD, especially in specimens that were not decalcified. The R201H substitution mutation of GNAS may be involved in the pathogenesis of polyostotic FD.

Heterotrimeric G proteins in the control of parathyroid hormone actions

Parathyroid hormone (PTH) is a key regulator of skeletal physiology and calcium and phosphate homeostasis. It acts on bone and kidney to stimulate bone turnover, increase the circulating levels of 1,25 dihydroxyvitamin D and calcium and inhibit the reabsorption of phosphate from the glomerular filtrate. Dysregulated PTH actions contribute to or are the cause of several endocrine disorders. This calciotropic hormone exerts its actions via binding to the PTH/PTH-related peptide receptor (PTH1R), which couples to multiple heterotrimeric G proteins, including G_s and G_q/11 Genetic mutations affecting the activity or expression of the alpha-subunit of G_s, encoded by the GNAS complex locus, are responsible for several human diseases for which the clinical findings result, at least partly, from aberrant PTH signaling. Here, we review the bone and renal actions of PTH with respect to the different signaling pathways downstream of these G proteins, as well as the disorders caused by GNAS mutations.