A sensitive mutation-specific screening technique for GNAS1 mutations in cases of fibrous dysplasia: the first report of a codon 227 mutation in bone

Genetic diagnosis in acromegaly and gigantism: From research to clinical practice

It is usually considered that only 5% of all pituitary neuroendocrine tumours are due to inheritable causes. Since this estimate was reported, however, multiple genetic defects driving syndromic and nonsyndromic somatotrophinomas have been unveiled. This heterogeneous genetic background results in overlapping phenotypes of GH excess. Genetic tests should be part of the approach to patients with acromegaly and gigantism because they can refine the clinical diagnoses, opening the possibility to tailor the clinical conduct to each patient. Even more, genetic testing and clinical screening of at-risk individuals have a positive impact on disease outcomes, by allowing for the timely detection and treatment of somatotrophinomas at early stages. Future research should focus on determining the actual frequency of novel genetic drivers of somatotrophinomas in the general population, developing up-to-date disease-specific multi-gene panels for clinical use, and finding strategies to improve access to modern genetic testing worldwide.

A Case Series and Literature Review of Craniofacial Fibrous Dysplasia

Craniofacial fibro-osseous lesions (CFOLs) are a diverse group of relatively rare entities whose etiology ranges from reactive to dysplastic with a potential for malignant transformation. It is distinguished by the replacement of bone with fibrous tissue, that subsequently develops different degrees of calcification. Fibrous dysplasia (FD) is a component of the fibro-osseous lesion spectrum. The clinical spectrum of FD is wide, ranging from minor monostotic lesions affecting a single bone to devastating polyostotic disease involving the entire skeleton. FD produces asymmetry, which impairs face aesthetics. FD leads to bone differentiation, disintegration, and disorganization. It depicts a cellular collagenous stroma lacking mitotic figures and pleomorphism. Blood capillaries are evenly distributed, as are elongated trabeculae of woven or lamellar bone with uneven curves (often referred to as the Chinese letters pattern). Three types of FD patterns can be identified by computed tomography (CT) imaging: a cystic pattern, a homogeneously dense pattern, and a ground-glass pattern. The cornerstone of treatment is surgery, although the method varies depending on the location, size, and symptoms of the lesion. As an alternative to surgery, the use of bisphosphonates to reduce osteoclastic activity is under consideration. In this case series, we present three cases of FD involving the maxilla and mandible. We aim to correlate the clinical presentation, histological features, and radiographic findings, to promote early diagnosis, treatment, and better prognosis of the patient.

Choosing the Best Tissue and Technique to Detect Mosaicism in Fibrous Dysplasia/McCune-Albright Syndrome (FD/MAS)

GNAS-activating somatic mutations give rise to Fibrous Dysplasia/McCune-Albright syndrome (FD/MAS). The low specificity of extra-skeletal signs of MAS and the mosaic status of the mutations generate some difficulties for a proper diagnosis. We studied the clinical and molecular statuses of 40 patients referred with a clinical suspicion of FD/MAS to provide some clues. GNAS was sequenced using both Sanger and Next-Generation Sequencing (NGS). We were able to identify the pathogenic variants in 25% of the patients. Most of them were identified in the affected tissue, but not in blood. Additionally, NGS demonstrated the ability to detect more patients with mosaicism (8/34) than Sanger sequencing (4/39). Even if in some cases, the clinical information was not complete, we confirmed that, as in previous works, when the patients were young children with a single manifestation, such as hyperpigmented skin macules or precocious puberty, the molecular diagnosis was usually negative. In conclusion, as FD/MAS is caused by mosaic variants, it is essential to use sensitive techniques that allow for the detection of low percentages and to choose the right tissue to study. When not possible, and due to the low positive genetic rate, patients with FD/MAS should only be genetically tested when the clinical diagnosis is really uncertain.

A Rare Skeletal Disorder, Fibrous Dysplasia: A Review of Its Pathogenesis and Therapeutic Prospects

Fibrous dysplasia (FD) is a rare, non-hereditary skeletal disorder characterized by its chronic course of non-neoplastic fibrous tissue buildup in place of healthy bone. A myriad of factors have been associated with its onset and progression. Perturbation of cell-cell signaling networks and response outputs leading to disrupted building blocks, incoherent multi-level organization, and loss of rigid structural motifs in mineralized tissues are factors that have been identified to participate in FD induction. In more recent years, novel insights into the unique biology of FD are transforming our understandings of its pathology, natural discourse of the disease, and treatment prospects. Herein, we built upon existing knowledge with recent findings to review clinical, etiologic, and histological features of FD and discussed known and potential mechanisms underlying FD manifestations. Subsequently, we ended on a note of optimism by highlighting emerging therapeutic approaches aimed at either halting or ameliorating disease progression.

GNAS locus: bone related diseases and mouse models

GNASis a complex locus characterized by multiple transcripts and an imprinting effect. It orchestrates a variety of physiological processes via numerous signaling pathways. Human diseases associated with the GNAS gene encompass fibrous dysplasia (FD), Albright's Hereditary Osteodystrophy (AHO), parathyroid hormone(PTH) resistance, and Progressive Osseous Heteroplasia (POH), among others. To facilitate the study of the GNAS locus and its associated diseases, researchers have developed a range of mouse models. In this review, we will systematically explore the GNAS locus, its related signaling pathways, the bone diseases associated with it, and the mouse models pertinent to these bone diseases.

Brain and eye involvement in McCune-Albright Syndrome: clinical and translational insights

McCune-Albright Syndrome (MAS) is a rare mosaic (post-zygotic) genetic disorder presenting with a broad continuum clinical spectrum. MAS arises from somatic, activating mutations in the GNAS gene, which induces a dysregulated Gsα-protein signaling in several tissues and an increased production of intracellular cyclic adenosine monophosphate (cAMP). Overall, MAS is a rare disorder affecting less than 1/100,000 children and, for this reason, data establishing genotype-phenotype correlations remain limited. Affected individuals clinically present with a variable combination of fibrous dysplasia of bone (FD), extra-skeletal manifestations (including cafeí-au-lait spots) and precocious puberty which might also be associated to broad hyperfunctioning endocrinopathies, and also gastrointestinal and cardiological involvement. Central nervous system (CNS) and eye involvement in MAS are among the less frequently described complications and remain largely uncharacterized. These rare complications mainly include neurodevelopmental abnormalities (e.g., delayed motor development, cognitive and language impairment), CNS anomalies (e.g., Chiari malformation type I) and a wide array of ophthalmological abnormalities often associated with vision loss. The pathophysiological mechanisms underlying abnormal neurological development have not been yet fully elucidated. The proposed mechanisms include a deleterious impact of chronically dysregulated Gsα-protein signaling on neurological function, or a secondary (damaging) effect of (antenatal and/or early postnatal) hypercortisolism on early pre- and post-natal CNS development. In this Review, we summarize the main neurological and ophthalmological features eventually associated with the MAS spectrum, also providing a detailed overview of the potential pathophysiological mechanisms underlying these clinical complications.

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.

Comparison of the histopathological characteristics of diffuse sclerosing osteomyelitis of the mandible, chronic suppurative osteomyelitis, and craniofacial fibrous dysplasia

BACKGROUND

There are relatively few reports on the histopathological characteristics of diffuse sclerosing osteomyelitis of the mandible (DSOM), which is difficult to distinguish from chronic suppurative osteomyelitis (CSO) and craniofacial fibrous dysplasia (CFD). This study aimed to summarize and compare the histopathological characteristics of DSOM, CFD, and CSO.

MATERIALS AND METHODS

In this study, hematoxylin and eosin-stained sections of patients with DSOM, CSO, and CFD at the Peking University Hospital of Stomatology from 2015 to 2020 were retrieved. The histopathological characteristics were summarized, including new bone formation, inflammatory cell infiltration, bone trabecular morphology, osteoclasts, sequestrum, bacterial mass, and calcified spherules, similar to cementicles. The histopathological characteristics of DSOM, CSO, and CFD were compared, and the results were statistically analyzed.

RESULTS

In total, 50, 13, and 10 patients with DSOM, CSO, and CFD were included in this study, respectively. In terms of new bone formation, both DSOM and CSO showed reactive bone formation (p = 1), whereas CFD mainly showed fiber osteogenesis (p < 0.001). The inflammatory cells of DSOM were mainly lymphocytes and plasma cells, whereas those of CSO were mainly lymphocytes and neutrophils (p < 0.001), and there was usually no inflammatory cell infiltration in the CFD specimens (p < 0.001). DSOM, CSO, and CFD showed irregular bone trabeculae (p = 0.045, p = 0.703) and active osteoclasts (p1 = 0.189, p2 = 0.256). DSOM showed a small amount of bacterial mass but no sequestrum; neither of which was found in CFD (p = 1, p = 1), but it was common in CSO (p = 0.011 and p = 0.025). DSOM and CSO showed smooth and regular basophilic lines (p = 0.308), whereas CFD showed a rough and irregular basophilic line (p < 0.001).

CONCLUSIONS

The histopathological characteristics of the three diseases were partly similar, but there were evident differences. The main differences are the type of new bone formation, types and distribution of inflammatory cells, and presence of sequestrum and bacterial masses. These differences will help clinicians diagnose DSOM.

GNAS mutation analysis assists in differentiating chronic diffuse sclerosing osteomyelitis from fibrous dysplasia in the jaw

Chronic diffuse sclerosing osteomyelitis of the mandible (DSOM) and fibrous dysplasia (FD) are distinct lesions with overlapping clinicopathological features that complicate their diagnosis. This study aimed to evaluate the efficacy of GNAS mutation analysis in differentiating between these two conditions. DNA samples from patients with DSOM (n = 35) and FD (n = 29) were collected to analyze the presence of GNAS mutations in exons 8 and 9, the two previously reported hotspot regions, using polymerase chain reaction and direct sequencing. Twenty-four of 29 patients (83%) with FD showed missense mutations in codon 201 in exon 8, whereas no mutation was detected in exon 9. No mutations were found in any of the 35 cases with DSOM. We also identified one case with an uncertain diagnosis due to overlapping clinicopathological features of DSOM and FD. A Q227H mutation was detected in this case, that confirmed the diagnosis of FD. Taken together, the findings indicate that mutational analysis of the GNAS is a reliable approach to differentiate between DSOM and FD of the jaw.

Precocious Pseudo-puberty in a Two-year-old Girl, Presenting with Bilateral Ovarian Enlargement and Progressing to Unilateral Juvenile Granulosa Cell Tumour

Ovarian causes of precocious pseudo-puberty (PPP) include McCune-Albright syndrome (MAS) and juvenile granulosa cell tumour (JGCT). We describe a case of PPP in which bilateral ovarian enlargement with multiple cysts progressed to unilateral JGCT. A girl aged 2.17 years presented with three months of breast development, and rapid growth. Examination showed tall stature, height +2.6 standard deviations, Tanner stage B3P2A1. A single café au lait patch was noted. Bone age was advanced at 5 years. Pelvic ultrasound showed bilaterally enlarged ovaries (estimated volumes 76 mL on the left, 139 mL on the right), each containing multiple cysts. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) values before/after gonadotrophin administration were 0.43/0.18 and <0.1/<0.1 mUI/mL, serum estradiol 130 pg/mL, (prepubertal range <20 pg/mL). PPP of ovarian origin was diagnosed, and tamoxifen 20 mg daily started. However, after only seven weeks height velocity escalated and breast development increased to B3-4 with menorrhagia. Basal/stimulated LH and FSH were still suppressed at 0.13/0.25 and <0.1/<0.1 mUI/mL and, serum estradiol 184 pg/mL. Repeat imaging now showed normal right ovary (volume 1.8 mL) and a large left-sided vascular solid/cystic ovarian tumour which was excised (weight 850 g). Histology showed JGCT, International Federation of Gynecology and Obstetrics stage IA. DNA from tumour tissue showed no mutation in GNAS, exon 3 of AKT1 (which contains a mutational hotspot) or FOXL2. The observation that bilateral ovarian activity progressed to unilateral development of JGCT in this patient is novel. This case highlights current uncertainties in the ontology of JGCT, and its possible relationship with MAS.

A rare pediatric case of McCune-Albright syndrome with acute visual disturbance: Case report

RATIONALE

McCune-Albright syndrome (MAS) is a rare disorder characterized by clinical findings, which includes fibrous dysplasia (FD). FD is a benign tumor that leads to increased rates of bone fracture. In some MAS cases with FD, facial deformities, severe pain, and orbital neuropathies are complicated. Aneurysmal bone cyst (ABC) is a benign bone tumor and rare complication of FD.

PATIENT CONCERNS

A 9-year-old boy was admitted to our hospital because of acute visual disturbance.

DIAGNOSIS AND INTERVENTIONS

The patient was clinically diagnosed as ABC complicated with MAS, and he underwent surgery.

OUTCOMES

After the surgery, his sight became normal. Recurrence of ABC and visual disturbance was not observed in 3 years. Genetic analysis of a tissue sample from the ABC lesion by next-generation sequencing revealed a somatic activating GNAS mutation.

LESSONS

To the best of our knowledge, this is the first case report of MAS causing optic neuropathy complicated with ABC. ABC complicated with MAS is extremely rare, but it should be considered as a possible diagnosis in patients with acute visual loss and facial swelling. In addition, our case had OAS, which is an uncommon syndrome and a rare complication in ABC with MAS, and rapid decompression of the ABC was effective in improving the patient's eyesight.

Circulating tumour DNA is a promising biomarker for risk stratification of central chondrosarcoma with IDH1/2 and GNAS mutations

Chondrosarcoma (CS) is a rare tumour type and the most common primary malignant bone cancer in adults. The prognosis, currently based on tumour grade, imaging and anatomical location, is not reliable, and more objective biomarkers are required. We aimed to determine whether the level of circulating tumour DNA (ctDNA) in the blood of CS patients could be used to predict outcome. In this multi-institutional study, we recruited 145 patients with cartilaginous tumours, of which 41 were excluded. ctDNA levels were assessed in 83 of the remaining 104 patients, whose tumours harboured a hotspot mutation in IDH1/2 or GNAS. ctDNA was detected pre-operatively in 31/83 (37%) and in 12/31 (39%) patients postoperatively. We found that detection of ctDNA was more accurate than pathology for identification of high-grade tumours and was associated with a poor prognosis; ctDNA was never associated with CS grade 1/atypical cartilaginous tumours (ACT) in the long bones, in neoplasms sited in the small bones of the hands and feet or in tumours measuring less than 80 mm. Although the results are promising, they are based on a small number of patients, and therefore, introduction of this blood test into clinical practice as a complementary assay to current standard-of-care protocols would allow the assay to be assessed more stringently and developed for a more personalised approach for the treatment of patients with CS.

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.

Genotype-Phenotype Correlation in Fibrous Dysplasia/McCune-Albright Syndrome

CONTEXT

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare bone and endocrine disorder resulting in fractures, pain, and disability. There are no targeted or effective therapies to alter the disease course. Disease arises from somatic gain-of-function variants at the R201 codon in GNAS, replacing arginine by either cysteine or histidine. The relative pathogenicity of these variants is not fully understood.

OBJECTIVE

This work aimed 1) to determine whether the most common GNAS variants (R201C and R201H) are associated with a specific clinical phenotype, and 2) to determine the prevalence of the most common GNAS variants in a large patient cohort.

METHODS

This retrospective cross-sectional analysis measured the correlation between genotype and phenotype characterized by clinical, biochemical, and radiographic data.

RESULTS

Sixty-one individuals were genotyped using DNA extracted from tissue or circulating cell-free DNA. Twenty-two patients (36.1%) had the R201C variant, and 39 (63.9%) had the R201H variant. FD skeletal disease burden, hypophosphatemia prevalence, fracture incidence, and ambulation status were similar between the 2 groups. There was no difference in the prevalence of endocrinopathies, ultrasonographic gonadal or thyroid abnormalities, or pancreatic involvement. There was a nonsignificant association of cancer with the R201H variant.

CONCLUSION

There is no clear genotype-phenotype correlation in patients with the most common FD/MAS pathogenic variants. The predominance of the R201H variant observed in our cohort and reported in the literature indicates it is likely responsible for a larger burden of disease in the overall population of patients with FD/MAS, which may have important implications for the future development of targeted therapies.

Comparing Clinical and Radiographic Characteristics of Chronic Diffuse Sclerosing Osteomyelitis and Craniofacial Fibrous Dysplasia in the Mandible

PURPOSE

Differential diagnosis of chronic diffuse sclerosing osteomyelitis of the mandible (DSOM) and craniofacial fibrous dysplasia (CFD) involving the mandible is challenging. The purpose of this study was to explore the differences of the clinical and radiographic characteristics between these 2 conditions.

PATIENTS AND METHODS

In this retrospective cross-sectional, blinded, comparative study, clinical and imaging data of patients with DSOM and CFD at the Peking University Hospital of Stomatology from 2012 to 2018 were retrieved. Clinical characteristics, mainly pain, swelling, and trismus, and radiographic findings, including sclerosis, lysis, and subperiosteal bone formation, were evaluated. The t test, χ² test, and Fisher-Freeman-Halton test were used to determine differences.

RESULTS

Thirty-seven patients with DSOM and 32 patients with CFD were included (mean ages, 24.2 and 28.4 years, respectively); both groups showed a female predilection. DSOM (91.9%) and CFD (84.4%) were mainly unilateral. Patients with DSOM mainly presented with pain (94.6%), soft-tissue swelling (100.0%), and trismus (54.1%), whereas those with CFD did not experience pain (90.6%) and showed bone enlargement (87.5%) without trismus (6.3%). Panoramic radiographs and computed tomography scans of patients with DSOM showed subperiosteal bone formation, cortex lysis, and poorly demarcated cortex, whereas those patients with CFD mainly showed moderate-to-severe bone expansion, well-demarcated cortex, and tooth and mandibular canal displacement.

CONCLUSIONS

These findings emphasize the importance of clinical and radiographic features in differentiating between DSOM and CFD. Pain, soft-tissue or bone-tissue swelling, subperiosteal bone formation, clarity of the boundary of the cortex and medulla, and continuity of the cortical bone are key points facilitating differentiation.

Undifferentiated Pleomorphic Sarcoma Arising in a Fibrous Dysplasia Confirmed by GNAS Mutation Analysis: A Case Report

CASE

We report the case of a 78-year-old woman with undifferentiated pleomorphic sarcoma (UPS) of the proximal femur arising in a previous site of fibrous dysplasia (i.e., a liposclerosing myxofibrous tumor) that had been treated 4 years earlier with curetted surgery. GNAS mutation was detected in both the previous benign lesion and the UPS.

CONCLUSION

Genetic analysis is useful in demonstrating the origin of the tumor especially in fibrous dysplasia with severe degeneration that have undergone malignant transformation.

The Distinct Role of the Extra-Large G Protein ɑ-Subunit XLɑs

GNAS is one of the most complex gene loci in the human genome and encodes multiple gene products including Gsα, XLαs, NESP55, A/B, and AS transcripts. XLαs, the extra-large G protein ɑ-subunit, is paternally expressed. XLɑs and Gsɑ share the common 2-13 exons with different promoters and first exons. Therefore, XLɑs contains most of the functional domains of Gsα including receptor and effector binding sites. In vitro studies suggest a "Gsɑ"-like function of XLɑs regarding the stimulation of cAMP generation in response to receptor activation with different cellular actions. However, it is unclear whether XLαs has an important physiological function in humans. Pseudopseudohypoparathyroidism (PPHP) and progressive osseous heteroplasia (POH) are caused by paternally inherited mutations of GNAS. Maternal uniparental disomy of chromosome 20 [UPD(20)mat] lacks paternal chromosome 20. Therefore, the phenotypes of these diseases may be secondary to the abnormal functions of XLɑs, at least partly. From the phenotypes of human diseases like PPHP, POH, and UPD(20)mat, as well as some animal models with deficient XLɑs functions, it could be seen that XLɑs is involved in the growth and development of the mammalian fetus, plays a different role in glucose, lipid, and energy metabolism when compared with Gsɑ, and could prevent heterotopic ossification in humans and mice. More in vivo and in vitro studies, especially the development of conditional XLɑs knockout mice, are needed to clarify the physiopathologic roles and related signal pathways of XLɑs.

DIAGNOSIS OF ENDOCRINE DISEASE: Mosaic disorders of FGF23 excess: Fibrous dysplasia/McCune-Albright syndrome and cutaneous skeletal hypophosphatemia syndrome

Fibrous dysplasia/McCune-Albright Syndrome (FD/MAS), arising from gain-of-function mutations in Gαs, and cutaneous skeletal hypophosphatemia syndrome (CSHS), arising from gain-of-function mutations in the Ras/MAPK pathway, are strikingly complex, mosaic diseases with overlapping phenotypes. Both disorders are defined by mosaic skin and bone involvement, and both are complicated by increased FGF23 production. These similarities have frequently led to mis-diagnoses, primarily in patients with CSHS who are often assumed to have FD/MAS. The intriguing similarities in skeletal involvement in these genetically distinct disorders have led to novel insights into FGF23 physiology, making an understanding of FD/MAS and CSHS relevant to both clinicians and researchers interested in bone and endocrine disorders. This review will give an overview of FD/MAS and CSHS, focusing on the roles of mosaicism and FGF23 in the pathogenesis and clinical presentation of these disorders.

Fibrous Dysplasia/McCune-Albright Syndrome: A Rare, Mosaic Disease of Gα s Activation

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare disorder of striking complexity. It arises from somatic, gain-of-function mutations in GNAS, leading to mosaic Gα s activation and inappropriate production of intracellular cyclic adenosine monophosphate (cAMP). The clinical phenotype is largely determined by the location and extent of affected tissues, and the pathophysiological effects of Gα s activation within these tissues. In bone, Gα s activation results in impaired differentiation of skeletal stem cells, leading to discrete skeletal lesions prone to fracture, deformity, and pain. Extraskeletal manifestations include a variable combination of hyperpigmented macules and hyperfunctioning endocrinopathies. Distinctive age-related changes in disease development has key effects on histologic, radiographic, and clinical features. FD/MAS thus presents along a uniquely broad clinical spectrum, and the resulting challenges in diagnosis and management can be difficult for clinicians. This review presents FD/MAS in the context of a mosaic disorder of Gα s activation, providing an intellectual framework within which to understand, evaluate, and treat this interesting disease. It includes a comprehensive summary of current understanding of FD/MAS pathogenesis, and a detailed discussion of clinical presentation and management. Critical areas of unmet need are highlighted, including discussion of key challenges and potential solutions to advance research and clinical care in FD/MAS.

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.

Best practice management guidelines for fibrous dysplasia/McCune-Albright syndrome: a consensus statement from the FD/MAS international consortium

Fibrous Dysplasia / McCune Albright syndrome (FD/MAS) represents a wide spectrum of diseases due to somatic gain-of-function mutations of the GNAS gene. The mutation leads to overactivity in the target tissues and to a wide phenotype of clinical features that vary in severity and age of onset. The rarity of the disease and its variable presentation to multiple specialities often leads to misdiagnosis and inappropriate variability in investigations and treatments. To address this, our international consortium of clinicians, researchers, and patients’ advocates has developed pragmatic clinical guidelines for best clinical practice for the definition, diagnosis, staging, treatment and monitoring for FD/MAS to empower patients and support clinical teams in both general and specialised healthcare settings. With the lack of strong evidence to inform care, the guidelines were developed based on review of published literature, long-standing extensive experience of authors, input from other healthcare professionals involved in the care of FD/MAS patients and feedback from patients and patient groups across the globe. This has led to the formulation of a set of statements to inform healthcare professionals, patients, their families, carers and patient groups of the best practice of care. It is anticipated the implementation of these recommendations will lead to improvement in the care of patients with FD/MAS internationally.

Multi-analytic study of a probable case of fibrous dysplasia (FD) from certosa monumental cemetery (Bologna, Italy)

OBJECTIVE

To evaluate, via a multidisciplinary approach, a distinctive paleopathological condition believed to be fibrous dysplasia, found on a 19th/20th century skeleton from Certosa Monumental Cemetery, Bologna, Italy.

MATERIALS

A skeletonized cranium and mandible recovered from an ossuary in 2014.

METHODS

Pathological alterations were analysed by radiological examination, dental macrowear, histopathological and genetic analyses.

RESULT

The skeleton is believed to be an adult male. Differential diagnoses include Paget's disease, McCune-Albright syndrome, osteochondroma and osteosarcoma. The radiographic findings, along with the solitary nature of the lesions, are strong evidence for the diagnosis of fibrous dysplasia (FD). Genetic analysis further revealed a frequency of ˜1% of mutant alleles with the R201C substitution, one of the post-zygotic activating mutation frequently associated with FD.

CONCLUSIONS

The multi-analytical method employed suggests a diagnosis of monostotic form of FD. The diagnostic design incorporates multiple lines of evidence, including macroscopic, histopathological, and genetic analyses.

SIGNIFICANCE

Through the use of a multi-analytic approach, robust diagnoses can be offered. This case serves as one of the oldest examples of FD from an historical context. The genetic mutation detected, associated with FD, has not been previously reported in historical/ancient samples.

Fibrous Dysplasia of Bone and McCune-Albright Syndrome: A Bench to Bedside Review

Fibrous dysplasia is an uncommon mosaic disorder in which bone is replaced by structurally unsound fibro-osseous tissue. It is caused by the sporadic post-zygotic activating mutations in GNAS, resulting in dysregulated Gα_S-protein signaling in affected tissues. This manifests on a broad clinical spectrum ranging from insignificant solitary lesions to severe disease with deformities, fractures, functional impairment, and pain. Fibrous dysplasia may present in isolation or in association with hyperfunctioning endocrinopathies and café-au-lait macules, known as McCune-Albright Syndrome. This review summarizes the current understanding of pathophysiology in fibrous dysplasia, describes key pre-clinical and clinical investigations, and details the current approach to diagnosis and management.

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.

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.

An update of molecular pathology of bone tumors. Lessons learned from investigating samples by next generation sequencing

The last decade has seen the majority of primary bone tumor subtypes become defined by molecular genetic alteration. Examples include giant cell tumour of bone (H3F3A p.G34W), chondroblastoma (H3F3B p.K36M), mesenchymal chondrosarcoma (HEY1-NCOA2), chondromyxoid fibroma (GRM1 rearrangements), aneurysmal bone cyst (USP6 rearrangements), osteoblastoma/osteoid osteoma (FOS/FOSB rearrangements), and synovial chondromatosis (FN1-ACVR2A and ACVR2A-FN1). All such alterations are mutually exclusive. Many of these have been translated into clinical service using immunohistochemistry or FISH. 60% of central chondrosarcoma is characterised by either isocitrate dehydrogenase (IDH) 1 or IDH2 mutations distinguishing them from other cartilaginous tumours. In contrast, recurrent alterations which are clinically helpful have not been found in high grade osteosarcoma. High throughput next generation sequencing has also proved valuable in identifying germ line alterations in a significant proportion of young patients with primary malignant bone tumors. These findings will play an increasing role in reaching a diagnosis and in patient management.

Karyotyping and analysis of GNAS locus in intramuscular myxomas

Intramuscular myxoma is a benign soft tissue tumor about which very limited genetic information exists. We studied 68 intramuscular myxomas by means of chromosome banding analysis finding abnormal karyotypes in 21 of them. The most clearly nonrandom involvement was of chromosome 8 which was found gained in seven tumors (+8 was the sole change in five myxomas) and structurally rearranged in another two. Since mutation of the gene GNAS (20q13) has been implicated in the pathogenesis of both solitary and hereditary multiple myxomas, we assessed the transcription and mutation status of this gene in five tumors from which we had suitable RNA. All five intramuscular myxomas expressed biallelic transcripts. The mutated GNAS allele found in one tumor was also biallelically transcribed. In none of the five myxomas were maternally expressed transcripts detected. Collectively, the data suggest that intramuscular myxomas have acquired genetic abnormalities that often include chromosome 8 changes but may also involve alterations of GNAS. To what extent these aberrations are pathogenetically important, remains uncertain.

Digital PCR analysis of circulating tumor DNA: a biomarker for chondrosarcoma diagnosis, prognostication, and residual disease detection

Conventional chondrosarcoma is the most common primary bone tumor in adults. Prognosis corresponds with tumor grade but remains variable, especially for individuals with grade (G) II disease. There are currently no biomarkers available for monitoring or prognostication of chondrosarcoma. Circulating tumor DNA (ctDNA) has recently emerged as a promising biomarker for a broad range of tumor types. To date, little has been done to study the presence of ctDNA and its potential utility in the management of sarcomas, including chondrosarcoma. In this study, we have assessed ctDNA levels in a cohort of 71 patients, 32 with sarcoma, including 29 individuals with central chondrosarcoma (CS) and 39 with locally aggressive and benign bone and soft tissue tumors, using digital PCR. In patients with CS, ctDNA was detected in pretreatment samples in 14/29 patients, which showed clear correlation with tumor grade as demonstrated by the detection of ctDNA in all patients with GIII and dedifferentiated disease (n = 6) and in 8/17 patients with GII disease, but never associated with GI CS. Notably detection of ctDNA preoperatively in GII disease was associated with a poor outcome. A total of 14 patients with CS had ctDNA levels assessed at multiple time points and in most patients there was a clear reduction following surgical removal. This research lays the foundation for larger studies to assess the utility of ctDNA for chondrosarcoma diagnosis, prognostication, early detection of residual disease and monitoring disease progression.

Giant Cell-Containing Tumors of Bone

Giant cell-containing tumors of bone are characterized morphologically by the presence of numerous osteoclastic giant cells. Correlation of clinical, radiologic, and laboratory findings is required for accurate histopathologic diagnosis and treatment of a giant cell-containing tumor of bone. In differential diagnosis, it is particularly important to note the age of the patient and the skeletal location of the lesion. This article considers the range of neoplastic and nonneoplastic lesions, which histologically contain numerous osteoclastic giant cells, and focuses on several lesions that frequently enter into the differential diagnosis.

GNAS Mutations in Fibrous Dysplasia: A Comparative Study of Standard Sequencing and Locked Nucleic Acid PCR Sequencing on Decalcified and Nondecalcified Formalin-fixed Paraffin-embedded Tissues

It is well known that fibrous dysplasia (FD) is characterized by the presence of activating mutations involving G-nucleotide binding protein-α subunit (GNAS) involving codon R201 and rarely codon 227 with a mutation frequency between 45% and 93%. Herein, we investigate the sensitivity of detection of GNAS mutations in exons 8 and 9 using a standard and a highly sensitive locked nucleic acid polymerase chain reaction (LNA-PCR) sequencing in 52 cases of FD. In view of the recent report of GNAS mutations in a small number of low-grade osteosarcomas, we also tested in addition 12 cases of low-grade osteosarcomas. GNAS exon 8 mutations p.R201H (31%), p.R201C (15%), and p.R201S (2%) were identified in 50% of FD cases. LNA-PCR sequencing identified only 1 positive case within the mutation negative cases tested by standard PCR and Sanger sequencing. No mutations were identified in any of the low-grade osteosarcomas by standard and LNA-PCR sequencing. There was no association between age, site, size, specimen type, and mutational status. No exon 9 or codon 227 mutations were identified in any of tested cases. There was a significant difference in the sensitivity of the assay between decalcified and nondecalcified FDs (31% vs. 70%, P=0.002). LNA-PCR has no added value in enhancing detection sensitivity for GNAS mutations in FD. In addition to decalcification, innate somatic mosaicism contributes to the decreased sensitivity in mutation detection.

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.

Patients with McCune-Albright syndrome have a broad spectrum of abnormalities in the gastrointestinal tract and pancreas

McCune-Albright Syndrome (MAS) is a rare sporadic syndrome caused by post-zygotic mutations in the GNAS oncogene, leading to constitutional mosaicism for these alterations. Somatic activating GNAS mutations also commonly occur in several gastrointestinal and pancreatic neoplasms, but the spectrum of abnormalities in these organs in patients with MAS has yet to be systematically described. We report comprehensive characterization of the upper gastrointestinal tract in seven patients with MAS and identify several different types of polyps, including gastric heterotopia/metaplasia (7/7), gastric hyperplastic polyps (5/7), fundic gland polyps (2/7), and a hamartomatous polyp (1/7). In addition, one patient had an unusual adenomatous lesion at the gastroesophageal junction with high-grade dysplasia. In the pancreas, all patients had endoscopic ultrasound findings suggestive of intraductal papillary mucinous neoplasm (IPMN), but only two patients met the criteria for surgical intervention. Both of these patients had IPMNs at resection, one with low-grade dysplasia and one with high-grade dysplasia. GNAS mutations were identified in the majority of lesions analyzed, including both IPMNs and the adenomatous lesion from the gastroesophageal junction. These studies suggest that there is a broad spectrum of abnormalities in the gastrointestinal tract and pancreas in patients with MAS and that patients with MAS should be evaluated for gastrointestinal pathology, some of which may warrant clinical intervention due to advanced dysplasia.

Fibrous dysplasia of bone: craniofacial and dental implications

Fibrous dysplasia (FD) is a rare bone disease caused by postzygotic somatic activating mutations in the GNAS gene, which lead to constitutive activation of adenylyl cyclase and elevated levels of cyclic AMP, which act on downstream signaling pathways and cause normal bone to be replaced with fibrous tissue and abnormal (woven) bone. The bone disease may occur in one bone (monostotic), multiple bones (polyostotic), or in combination with hyperfunctioning endocrinopathies and hyperpigmented skin lesions (in the setting of McCune-Albright Syndrome). FD is common in the craniofacial skeleton, causing significant dysmorphic features, bone pain, and dental anomalies. This review summarizes the pathophysiology, clinical findings, and treatment of FD, with an emphasis on the craniofacial and oral manifestations of the disease.

Multifocal low-grade central osteosarcoma: a rare case

Low-grade central osteosarcoma (LGCOS) is a rare variant of osteosarcoma. We present a rare case of multifocal LGCOS located in two distinct skeletal sites, initially noted as incidental findings on imaging for distant traumatic pathology. Both sites seemed small and innocuous on initial imaging, and were quiescent clinically, illustrating the value of close interval multimodal surveillance scanning.

Mutation Profiling of Usual Ductal Hyperplasia of the Breast Reveals Activating Mutations Predominantly at Different Levels of the PI3K/AKT/mTOR Pathway

Usual ductal hyperplasia (UDH) of the breast is generally regarded as a nonneoplastic proliferation, albeit loss of heterozygosity has long been reported in a part of these lesions. To gain deeper insights into the molecular drivers of these lesions, an extended mutation profiling was performed. The coding regions of 409 cancer-related genes were investigated by next-generation sequencing in 16 cases of UDH, nine unassociated with neoplasia (classic) and seven arising within papillomas. Phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (mTOR) activation was investigated by phosphorylated AKT, mTOR, and S6 immunohistochemistry. Of 16 lesions, 10 (63%) were mutated; 56% of classic lesions were unassociated with neoplasia, and 71% of lesions arose in papillomas. Fourteen missense mutations were detected: PIK3CA [6 (43%) of 14], AKT1 [2 (14%) of 14], as well as GNAS, MTOR, PIK3R1, LPHN3, LRP1B, and IGF2R [each 1 (7%) of 14]. Phosphorylated mTOR was seen in 83% and phosphorylated S6 in 86% of evaluable lesions (phospho-AKT staining was technically uninterpretable). In conclusion, UDH displays mutations of the phosphatidylinositol 3-kinase/AKT/mTOR axis at different levels, with PIK3R1, MTOR, and GNAS mutations not previously described. Specifically, oncogenic G-protein activation represents a yet unrecognized route to proliferation in UDH. On the basis of evidence of activating mutations, loss of heterozygosity, and a mass forming proliferation, we propose that UDH is most appropriately viewed as an early neoplastic intraductal proliferation.

The H3F3 K36M mutant antibody is a sensitive and specific marker for the diagnosis of chondroblastoma

AIMS

We recently reported that 95% of chondroblastomas harbour a p.K36M mutation in either H3F3A (chromosome 1) or H3F3B (chromosome 17), with the majority involving H3F3B. The aim of this study was to assess the expression of the K36M-mutated protein by immunohistochemistry in a large group of tumours.

METHODS AND RESULTS

One thousand eight hundred and ninety-four tumours, including 85 chondroblastomas and 10 clear-cell chondrosarcomas, were studied; of these, 82 chondroblastomas and one clear-cell chondrosarcoma known to harbour the H3F3 p.K36M mutation expressed the mutated protein. Three chondroblastomas and nine clear-cell chondrosarcomas wild type for H3F3A/H3F3B were negative for p.K36M immunoexpression. The remaining 1799 cases tested, 545 of which were known to be wild type for the H3F3A and H3F3B p.K36M mutations, included 1047 primary bone tumours, and 507 soft tissue and joint tumours. Two hundred and forty-five other tumour types not expected to harbour the mutation were negative for p.K36M immunoexpression.

CONCLUSIONS

Our data demonstrate the specificity and sensitivity of this immunomarker, and will be a useful adjunct for reaching a diagnosis of chondroblastoma.

Rare giant frontal sinus osteoma mimicking fibrous dysplasia

OBJECTIVE

To present the first report of a giant frontal sinus osteoma treated by excision and single-stage reconstruction with custom-made titanium cranioplasty and left orbital roof prostheses.

CASE REPORT

A 31-year-old man with a history of chronic frontal sinusitis presented with a deforming, painless, midline forehead swelling of 11 years' duration, which had been treated unsuccessfully in Nigeria. Differential diagnosis included both benign and malignant bony tumours. Computerised tomography revealed a giant bony frontal sinus tumour extending beyond the sinus roof and breaching the left orbit, consistent with fibrous dysplasia. Given the extent of the tumour, open craniectomy was performed for surgical extirpation. Histological analysis identified multiple osteomas. This surgical approach achieved excellent cosmesis, with no evidence of recurrence at 12-month follow up.

CONCLUSION

Forehead swelling may pose diagnostic and management dilemmas for the ENT surgeon; however, effective management is facilitated by a multidisciplinary approach.

Clinical Applications of Molecular Markers in Bone Tumors

Pathologic diagnosis of primary bone neoplasms can be challenging primarily due to rarity of the disease entities, overlapping imaging and histologic findings, and lack of tumor-specific immunohistochemical stains. Although slow to evolve, in recent years there has been a rapid advance in the discovery of new and novel molecular markers in primary bone neoplasms, which has enhanced diagnostic accuracy and has shed light into their pathogenesis. Modern technological approaches such as next-generation sequencing including RNA sequencing are serving as "rapid discovery platforms" for new and novel mutations and translocations with diagnostic, prognostic, and possible therapeutic applicability. As next-generation sequencing technologies are finding their place in clinical laboratories, one could envision routine testing for mutations spanning across a gene or translocations with multiple breakpoints and partner genes. This review will focus on the clinical relevance and applicability of molecular markers in primary bone neoplasms with examples.

GNAS mutations are not detected in parosteal and low-grade central osteosarcomas

Parosteal osteosarcoma, low-grade central osteosarcoma, and fibrous dysplasia share similar histological features that may pose a diagnostic challenge. The detection of GNAS mutations in primary bone tumors has been useful in clinical practice for diagnosing fibrous dysplasia. However, the recent report of GNAS mutations being detected in a significant proportion of parosteal osteosarcoma challenges the specificity of this mutation. As the number of cases reported in this study was small we set out to determine if these results could be reproduced. We studied 97 formalin-fixed paraffin-embedded low-grade osteosarcomas from 90 patients including 62 parosteal osteosarcomas, of which MDM2 amplification was detected in 79%, 11 periosteal osteosarcomas and 24 low-grade central osteosarcoma samples. The mutational status of GNAS was analyzed in codons p.R201, p.Q227, and other less common GNAS alterations by bidirectional Sanger sequencing and/or next generation sequencing using the Life Technologies Ion Torrent platform. GNAS mutations were not detected in any of the low-grade osteosarcomas from which informative DNA was extracted. Our findings therefore support prior observations that GNAS mutations are highly specific for fibrous dysplasia and occur rarely, if ever, in parosteal and other low-grade osteosarcomas.

GNAS Spectrum of Disorders

The GNAS complex locus encodes the alpha-subunit of the stimulatory G protein (Gsα), a ubiquitous signaling protein mediating the actions of many hormones, neurotransmitters, and paracrine/autocrine factors via generation of the second messenger cAMP. GNAS gives rise to other gene products, most of which exhibit exclusively monoallelic expression. In contrast, Gsα is expressed biallelically in most tissues; however, paternal Gsα expression is silenced in a small number of tissues through as-yet-poorly understood mechanisms that involve differential methylation within GNAS. Gsα-coding GNAS mutations that lead to diminished Gsα expression and/or function result in Albright's hereditary osteodystrophy (AHO) with or without hormone resistance, i.e., pseudohypoparathyroidism type-Ia/Ic and pseudo-pseudohypoparathyroidism, respectively. Microdeletions that alter GNAS methylation and, thereby, diminish Gsα expression in tissues in which the paternal Gsα allele is normally silenced also cause hormone resistance, which occurs typically in the absence of AHO, a disorder termed pseudohypoparathyroidism type-Ib. Mutations of GNAS that cause constitutive Gsα signaling are found in patients with McCune-Albright syndrome, fibrous dysplasia of bone, and different endocrine and non-endocrine tumors. Clinical features of these diseases depend significantly on the parental allelic origin of the GNAS mutation, reflecting the tissue-specific paternal Gsα silencing. In this article, we review the pathogenesis and the phenotypes of these human diseases.

Two cases of multiple ossifying fibromas in the jaws

BACKGROUND

The clinicopathologic characteristics of multiple ossifying fibroma (OF) are unclear due to the condition's rarity, making diagnosis challenging. Sporadic multiple OFs must be distinguished from hyperparathyroidism-jaw tumour syndrome (HPT-JT) related OF and other fibro-osseous lesions.

METHODS

Multiple OF cases were identified from ossifying fibroma cases. Clinical data including age, sex, anatomic site, radiographic features, clinical impression, treatment and available follow-up data as well as serum calcium, phosphorus, and parathyroid hormone (PTH) were recorded. GNAS and HRPT2 genetic mutations were examined in the two present cases. Case reports of sporadic multiple ossifying fibroma and HPT-JT-related OF were also reviewed.

RESULTS

The two present cases were confirmed as sporadic multiple OF, with no genetic GNAS and HRPT2 mutations found. The incidence of sporadic multiple ossifying fibroma was 2.0% (2/102). The total 18 sporadic multiform OF cases were characterized as followed: 13 (72.2%) female; 5 (27.8%) male; mean age 28.6 years; 2/16 (11.1%) cases only in the mandible; 4/18 (22.2%) cases only in the maxilla; and 12/18 (66.7%) cases in both the maxilla and mandible. Radiographically, the lesions were radiolucent in 5/18 (27.8%) cases and mixed density in 13/18 (72.2%) cases. Along with 24 cases of HPT-JT related OF were reviewed, sixteen (66.7%) patients were diagnosed with a single lesion, and 8 patients (33.3%) were diagnosed with multiple jaw lesions.

CONCLUSIONS

Sporadic multiple OFs are very rare, but must be distinguished from HPT-JT related OF. We strongly recommend that patients diagnosed with multiple ossifying fibromas receive serum PTH testing and mutation screening of HRPT2.

VIRTUAL SLIDES

http://www.diagnosticpathology.diagnomx.eu/vs/1194507146115753.

Analysis of GNAS1 mutations in myxoid soft tissue and bone tumors

The aim of this study was to characterize the prevalence of GNAS1 mutations in various tumor types, including intramuscular myxomas, fibrous dysplasias, and other myxoid tumors and implications for malignant transformation. PCR and direct sequencing were applied to analyze GNAS1 mutation status using genomic DNA isolated from 97 formalin-fixed and paraffin-embedded samples, including 63 intramuscular myxomas, 19 various myxoid lesions, 8 cases of sporadically occurring fibrous dysplasia, and 7 cases of atrial myxoma. Mutations of GNAS1 were detected in 23 out of 63 (36.5%) intramuscular myxoma patients, with mutational hotspots R201H and R201C being equally affected. GNAS1 mutations in codon 201 were found in 5 out of 8 fibrous dysplasias (62.5%), while no mutations of GNAS1 were detected in the other studied entities, including atrial myxomas. GNAS1 mutation analysis has diagnostic value in screening patients with intramuscular myxoma and patients with fibrous dysplasia.