Activating Gs(alpha) mutation in intramuscular myxomas with and without fibrous dysplasia of bone

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.

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.

Postzygotic mutations and where to find them - Recent advances and future implications in the field of non-neoplastic somatic mosaicism

The technological progress of massively parallel sequencing (MPS) has triggered a remarkable development in the research on postzygotic mutations. Although the overwhelming majority of studies in the field focus on oncogenesis, non-neoplastic diseases are attracting more and more attention. The aim of this review was to summarize some of the most recent findings in the field of somatic mosaicism in diseases other than neoplastic events. We discuss the abundance and role of postzygotic mutations, with a special emphasis on disorders which occur only in a mosaic form (obligatory mosaic diseases; OMDs). Based on the list of OMDs compiled from the published literature and three databases (OMIM, Orphanet and MosaicBase), we demonstrate the prevalence of cancer-related genes across OMDs and suggest other sources to further explore OMDs and OMD-related genes. Additionally, we comment on some practical aspects related to mosaic diseases, such as approaches to tissue sampling, the MPS coverage required to detect variants at a very low frequency, as well as on bioinformatic and molecular tools dedicated to detect somatic mutations in MPS data.

Extent of Extraskeletal Manifestations of Fibrous Dysplasia/McCune-Albright Syndrome in Patients with Mazabraud's Syndrome

Mazabraud's syndrome (MZB) is a rare condition in which fibrous dysplasia of bone/the McCune-Albright syndrome (FD/MAS) co-exists with intramuscular myxomas. Both FD and the myxomas harbor the GNAS-mutation. Recent studies have shown that extraskeletal, GNAS-related features are associated with a more severe phenotype of FD/MAS. However, patients with MZB are often only seen by orthopedic surgeons. We therefore evaluated MZB patients seen in tertiary referral centers from the Netherlands (LUMC), USA (National Institutes of Health) and France (INSERM UMR 1033 (Lyos), Hôpital Edouard Herriot). All FD/MAS patients known in these centers with an additional diagnosis of a myxoma were included. Demographic information and data on disease extent and extraskeletal manifestations of FD/MAS such as precocious puberty (PP) or café-au-lait patches (CAL) were retrieved from patient's medical records. Thirty MZB patients were included: 20 women (67%) and 10 men (33%). Patients received a diagnosis of MZB (median 42 years, range 16-19) significantly later than the diagnosis of FD/MAS (median 30 years, range 0-60), p < 0.01. Twenty-six patients were diagnosed with polyostotic disease (87%). In 97% the myxoma was located near the skeletal FD lesion. The combination of MZB and MAS was made in 13 patients in whom PP (n = 7), CAL (n = 7), GH-excess (n = 3) and hyperthyroidism (n = 3) were present. Other extraskeletal features were (multinodular) goiter (n = 2) and thyroid cysts (n = 1). Furthermore, in this cohort of patients with MZB several (pre-)malignant tumors were observed; ductal carcinoma in situ of the breast in 3 patients (10%), breast cancer in 1 patient (3.3%), intra pancreatic mucinous neoplasms in 3 patients (10%) and liver adenomas in 2 patients (6.6%). A total of 47% of patients with MZB had an additional extraskeletal feature such as an endocrinopathy. In MZB, 87% of patients suffer from polyostotic FD, 43% of patients have extraskeletal GNAS-features such as an hyperfunctioning endocrinopathy and 30% (pre-)malignant tumors. We therefore advocate that MZB patients should undergo a complete screening and long-term follow-up for extent of bone disease, but also extraskeletal GNAS features of FD/MAS.

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.

Heterotrimeric G-protein, Gi1, is involved in the regulation of proliferation, neuronal migration, and dendrite morphology during cortical development in vivo

Heterotrimeric G-proteins are composed of α, β, and γ subunits, and function as signal transducers. Critical roles of the α-subunits of Gi/o family heterotrimeric G-proteins, Gαi2, and Gαo1, have so far been reported in brain development and neurodevelopmental disorders. In this study, we tried to clarify the role of Gαi1, α-subunit of another Gi/o family member Gi1, during corticogenesis, based on the recent identification of its gene abnormalities in neurodevelopmental disorders. In western blot analyses, Gαi1 was found to be expressed in mouse brain in a developmental stage-dependent manner. Morphological analyses revealed that Gαi1 was broadly distributed in cerebral cortex with relatively high expression in the ventricular zone (VZ) at embryonic day (E) 14. Meanwhile, Gαi1 was enriched in membrane area of yet unidentified early mitotic cells in the VZ and the marginal zone at E14. Acute knockdown of Gαi1 with in utero electroporation in cerebral cortex caused cell cycle elongation of the neural progenitor cells and promoted their cell cycle exit. Gαi1-deficient cortical neurons also exhibited delayed radial migration during corticogenesis, with abnormally elongated leading processes and hampered nucleokinesis. In addition, silencing of Gαi1 prevented basal dendrite development. The migration and dendritic phenotypes were at least partially rescued by an RNAi-resistant version of Gαi1. Collectively, these results strongly suggest a crucial role of Gi1 in cortical development, and disturbance of its function may cause deficits in synaptic network formation, leading to neurodevelopmental disorders.

Myxoid neoplasms of bone and soft tissue: a pattern-based approach

INTRODUCTION

The accurate diagnosis of musculoskeletal neoplasms is difficult but a pattern-based approach combined with ancillary testing has been shown to improve diagnostic accuracy. The pattern-based approach is particularly appropriate for myxoid lesions.

MATERIALS AND METHODS

The authors reviewed their personal experience of over 3 decades of diagnosing myxoid neoplasms of musculoskeletal lesions.

RESULTS

The authors found that myxoid lesions can be accurately classified based on cell type, nuclear atypia, presence of blood vessel fragments, as well as the results of immunohistochemical and molecular testing.

CONCLUSIONS

Musculoskeletal lesions with a prominence of myxoid or chondroid material in the background can be accurately diagnosed using pattern analysis and ancillary testing.

Monostotic Fibrous Dysplasia of the Lumbar Spine With Secondary Features of Solid Variant Aneurysmal Bone Cyst

Fibrous dysplasia is a benign, mass-forming disease of bone composed of abnormal fibrous and osseous elements that can be accompanied by endocrine dysfunction, skin pigmentation, and intramuscular myxomas. It is usually encountered as a solitary lesion in the tibia or femur but can develop in any bone and can be unifocal or multifocal. Difficulty arises when a solitary lesion is identified in an uncommon site or when there are prominent secondary changes, such as aneurysmal bone cyst (ABC). Molecular studies are available as an adjunct to histomorphology to aid distinction from other entities. GNAS mutations, present in greater than 70% of fibrous dysplasia cases, help in the distinction from primary ABC and low-grade osteosarcoma, which exhibit different molecular abnormalities. We report a case of monostotic fibrous dysplasia in a lumbar vertebral body with secondary change consisting of the solid variant of ABC.

A case of a myxoma within the obturator externus muscle

Intramuscular myxomas (IM) are rare benign tumors of mesenchymal origin. These tumors have a high myxoid content and a nonspecific radiologic appearance. Here we describe the case of a patient with an IM in an infrequent location; within the obturator externus muscle. A singular approach was utilized for the resection of this tumor in such rare location.

Despite IM being benign tumors, patients may require a surgical excision due to the difficulty of differentiating these tumors, with unreliable imaging features, from other myxoid soft tissue masses.

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.

Prevalence and Clinical Features of Mazabraud Syndrome: A Multicenter European Study

BACKGROUND

Mazabraud syndrome is a rare disorder, characterized by the presence of fibrous dysplasia (FD) with associated intramuscular myxomas. Data are scarce on the prevalence, clinical features, and natural history of this disorder and outcomes. In this multicenter study, we evaluated a series of patients from 6 European centers.

METHODS

All centers affiliated with the European Musculo-Skeletal Oncology Society (EMSOS) were invited to include data on all patients with Mazabraud syndrome who were seen between 1980 and 2015. The study investigated the prevalence of Mazabraud syndrome, the type, severity, and localization of FD lesions in relation to myxomas, the histopathology of myxomas, and results of GNAS-mutation analysis, when available.

RESULTS

Thirty-two patients (22 female) from 6 centers were included. The prevalence of Mazabraud syndrome was 2.2% in the combined cohort of 1,446 patients with FD, and the syndrome was diagnosed at a mean of 10.1 years after diagnosis of FD. The myxomas were predominantly localized in the upper leg. Excision was performed in 20 patients, recurrence occurred in 6 of these patients (30%) at a median of 8.5 years (range, 1.9 to 16.0 years), and revision surgery was necessary in 5 (25%). High cellularity of myxomas was associated with recurrence (p < 0.05). A GNAS mutation was identified in the myxoma tissue of 5 (83%) of 6 patients with GNAS-mutation analysis.

CONCLUSIONS

This study is the first, to our knowledge, to provide data on the prevalence of Mazabraud syndrome in a relatively large cohort. Although the outcomes of surgical resection were good, a quarter of the patients required revision surgery despite clear resection margins. High cellularity of myxomas was associated with recurrence. GNAS mutations were identified in 83% (5 of 6), emphasizing the shared origin of FD and myxomas. Our data show that patients with FD who have disproportionate complaints, irrespective of FD type, extent, or severity, should be investigated for the possible presence of myxomas.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

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.

Detection of GNAS mutations in intramuscular / cellular myxomas as diagnostic tool in the classification of myxoid soft tissue tumors

BACKGROUND

Intramuscular / cellular myxomas and low-grade myxofibrosarcomas are two different tumor entities with a significant histological overlap, especially if dealing with small biopsies. Despite the morphological similarities, they differ considerably in their biological behaviour. Intramuscular / cellular myxoma rarely shows signs of recurrence and never metastasizes, in contrast to myxofibrosarcoma that tends to recur more aggressively and to metastasize haematologically. Therefore, it is of great importance to distinguish these lesions - evaluation of GNAS mutation status could be of tremendous help.

METHODS

We reviewed 13 cases with intramuscular / cellular myxomas. The 13 cases included 5 men and 8 women, aged from 33 to 71 years (mean age 55.5 years). Immunohistochemistry was performed as well as next generation sequencing. Ten cases were located in the lower extremities and three cases were located in the upper extremities. Two lesions were initially misdiagnosed as a low-grade myxofibrosarcoma.

RESULTS

Performing next generation sequencing 12 out of 13 specimens showed a GNAS mutation.

CONCLUSIONS

Our findings demonstrate that GNAS mutations are more common in intramuscular / cellular myxomas, than had been reported in literature in the past. Next generation sequencing for determining GNAS mutation status on small biopsies or diagnostically challenging cases facilitates the diagnosis of intramuscular / cellular myxoma and separates this tumor entity from its mimics.

Head and neck manifestations of an undiagnosed McCune-Albright syndrome: clinicopathological description and literature review

Craniofacial fibrous dysplasia, characteristic of McCune-Albright syndrome (MAS), is usually present in patients with MAS-related acromegaly. We report here the first case of a patient with an undiagnosed MAS presenting with an acute hydrocephalus. A 21-year-old male with gigantism and craniofacial fibrous dysplasia consulted for rapidly progressive headache. An acute obstructive hydrocephalus due to a 39 × 35-mm cystic lesion in the third ventricle was discovered and operated, obtaining hydrocephalus resolution. Pathology described a colloid cyst material and a growth hormone-secreting pituitary adenoma. Genetic study revealed the mosaic GNAS R201H mutation in the pituitary tissue, confirming a MAS diagnosis. Adequate hormonal control was achieved postoperatively. Our results suggest that long-term untreated growth hormone excess in patients with MAS-related craniofacial fibrous dysplasia might end compromising cerebrospinal fluid flow. A prompt diagnosis and coordinated multidisciplinary treatment may help to avoid long-term deleterious impact of hyperfunctioning endocrinopathies in these patients.

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.

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.

An Interesting Case of Intramuscular Myxoma with Scapular Bone Lysis

Introduction. Intramuscular myxoma is a rare benign primitive tumor of the mesenchyme founded at the skeletal muscle level; it presents itself like an unpainful, slow-growing mass. Myxomas with bone lysis are even more rare; only 7 cases have been reported in the English literature, but never at the shoulder level. Case Presentation. We describe an 83-year-old patient with a growing mass in the deltoid muscle with unique scapular lysis, without any symptom. Magnetic resonance imaging (MRI) and a biopsy were performed and the diagnosis of intramuscular myxoma has been retained. In front of this diagnosis of nonmalignant lesion, the decision of a simple follow-up was taken. One year after this decision, the patient was still asymptomatic. Conclusion. In the presence of an intramuscular growing mass with associated bone lysis, intramuscular myxoma as well as malignant tumor should be evoked. MRI has to be part of the initial radiologic appraisal but biopsy is essential to confirm the diagnosis. By consensus, the standard treatment is surgical excision but conservative treatment with simple follow-up can be an option.

Role of a heterotrimeric G-protein, Gi2, in the corticogenesis: possible involvement in periventricular nodular heterotopia and intellectual disability

We analyzed the role of a heterotrimeric G-protein, Gi2, in the development of the cerebral cortex. Acute knockdown of the α-subunit (Gαi2) with in utero electroporation caused delayed radial migration of excitatory neurons during corticogenesis, perhaps because of impaired morphology. The migration phenotype was rescued by an RNAi-resistant version of Gαi2. On the other hand, silencing of Gαi2 did not affect axon elongation, dendritic arbor formation or neurogenesis at ventricular zone in vivo. When behavior analyses were conducted with acute Gαi2-knockdown mice, they showed defects in social interaction, novelty recognition and active avoidance learning as well as increased anxiety. Subsequently, using whole-exome sequencing analysis, we identified a de novo heterozygous missense mutation (c.680C>T; p.Ala227Val) in the GNAI2 gene encoding Gαi2 in an individual with periventricular nodular heterotopia and intellectual disability. Collectively, the phenotypes in the knockdown experiments suggest a role of Gαi2 in the brain development, and impairment of its function might cause defects in neuronal functions which lead to neurodevelopmental disorders.

Monosotic fibrous dysplasia and solitary intramuscular myxoma of the head and neck: A unique presentation of Mazabraud's syndrome and a literature review

Mazabraud's syndrome (MS) is a rare disease that is a combination of fibrous dysplasia and intramuscular myxomas. MS is a benign lesion and there is little data on the disease due to its low incidence. In the present study, the case of a 38-year-old patient who presented with a soft-tissue mass involving the masseter and swelling at the mandibular body and mandibular ramus is reported. Since the mandible is an important aesthetic and functional organ in the oral and maxillofacial region, surgery was primarily aimed at resecting the tumor, with good safety margins, and reconstructing the resultant defect. The lesions were pathologically diagnosed as MS. The unique features of this case included the painless and monostotic fibrous dysplasia, the solitary intramuscular myxomas involving the jaw and the male gender of the patient. MS usually occurs in the lower extremities, with an unusual predilection for the right limb; however, it rarely occurs in the head and neck region. A retrospective analysis of the clinical features and management of MS was also performed in the present study, together with a literature review. From the literature, it was concluded that the incidence of MS is ~2.3-fold greater in female patients than in male patients, and that the age of onset of MS ranges between 17 and 82 years, with an average age of 46.25 years.

Mazabraud's syndrome: Report of its first incidence in the Middle East and a literature review

INTRODUCTION

Mazabraud's syndrome, a rare benign disease with indolent course, is best described as an association between soft tissue myxoma and fibrous dysplasia of the bones. In this report, we describe the first case of this syndrome from Saudi Arabia.

CASE PRESENTATION

A 24-year-old male in overall good health status, presented with progressive left knee swelling over 6 years with no other associated symptoms. The swelling measured 5 cm in diameter, with smooth surface, and soft palpable texture. Radiological examination followed by histopathological examination of the excised mass confirmed our diagnosis of Mazabraud's syndrome. The patient was closely followed up with systematic examination with no recurrence.

DISCUSSION

Fibrous dysplasia, soft tissue myxoma and multiple endocrinological diseases like McCune-Albright syndrome characterize Mazabraud's syndrome. Furthermore, fibrous dysplasia is found to be associated with GNA1S gene mutation. Many patients can have asymptomatic course of the disease but may present with pathological fractures, pain, and limitation of movement when the myxoma is near the joints or just simple cosmetically disturbing swelling like in our case.

CONCLUSION

Patients with such presentation need to be investigated thoroughly to rule out associated diseases and to evaluate the extent of such pathology. The improvement of radiological modalities can help in narrowing the differential diagnosis and following the patient to early detect the recurrence or any malignant transformation of the condition.

Intramuscular myxoma of the paraspinal muscles: A case report and systematic review of the literature

Intramuscular myxoma (IM) is a rare mesenchymal tumor of the head and neck region. The current study reports a case of a 45-year-old man who presented with a painless neck mass. Imaging showed involvement of the levator scapulae and scalene muscles. Core needle biopsy was consistent with intramuscular myxoma. Surgical excision was performed and follow-up for 30 months showed no recurrence. The present study includes a systematic review of head and neck IMs, with a summary of the clinical and demographic parameters of all reported cases in the head and neck region. Surgery was curative in 28 of the 29 published cases, as well as in the current case (96.7%), with the lone recurrent tumor cured following re-resection. Females constituted 57% of the cases and the mean age was 49.7±20.4 years. Although uncommon, IM should be considered in the differential diagnosis of deep neck masses, and surgical excision is the treatment of choice with a low risk of recurrence.

Polyostotic fibrous dysplasia associated with intramuscular myxomas: Mazabraud syndrome

The authors report a new case of Mazabraud syndrome in a 69-year-old woman complaining of pain in her right thigh. Plain radiographs demonstrated radiological findings consistent with polyostotic fibrous dysplasia of the right femur and tibia. Magnetic resonance imaging (MRI) study showed soft tissue tumors located in the vastus intermedius muscle with typical signal features of intramuscular myxomas. Biopsy was not performed because of its benign nature. Symptomatic treatment was prescribed and all the lesions remained 1 year after the diagnosis.

Cell cycle and apoptosis regulatory proteins, proliferative markers, cell signaling molecules, CD209, and decorin immunoreactivity in low-grade myxofibrosarcoma and myxoma

The histologic differential diagnosis between intramuscular myxoma and low-grade myxofibrosarcoma can be quite difficult in some cases. To identify a diagnostic immunohistochemical marker, we compared the staining profiles of 19 different antigens, including cell cycle proteins, apoptosis proteins, and proliferative markers, and selected other signaling and structural proteins in these two tumors. Ten cases each of intramuscular myxoma and low-grade myxofibrosarcoma were stained with antibodies directed against apoptosis regulatory proteins (Bcl2, activated caspase-3, phospho-H2A.X, and cleaved PARP), cell cycle regulatory proteins (Rb1, Cyclin-A, CDKN1B, and Cdt1), proliferative markers (KI67, MCM2, phospho-histone H3, and geminin), cell signalling molecules (c-Myc, EGF, EGFR, PLA2G4A, and HSP90), a dendritic cell marker (CD209), and the extracellular matrix proteoglycan decorin. Staining patterns of myxoma and myxofibrosarcoma were compared using Fisher's exact test and the Mann-Whitney test. For each potential diagnostic marker studied, the proportions of cases scored as positive on both dichotomous or ordinal scales were not significantly different between myxoma and myxofibrosarcoma. Myxoma and myxofibrosarcoma share a common immunophenotype for each of the markers studied. Distinction between these tumors is still predominantly based on morphologic criteria.

GNAS mutation is a frequent event in pancreatic intraductal papillary mucinous neoplasms and associated adenocarcinomas

In contrast to pancreatic ductal adenocarcinomas (PDAs), intraductal papillary mucinous neoplasms (IPMNs) frequently harbour GNAS mutations. To characterise GNAS-mutated pancreatic carcinomas, we examined mutations of GNAS and KRAS in 290 pancreatic adenocarcinomas and 77 pancreatic intraepithelial neoplasias (PanINs). In 64 % (39/61) of IPMNs and 37 % (11/30) of IPMN-associated adenocarcinomas, a GNAS mutation was found. GNAS mutations were frequent (78 %, 7/9) in mucinous carcinomas, with or without associated IPMN. In contrast, GNAS mutations were rarely observed in PDAs (1 %, 1/88) and PanINs (3 %, 2/77), and not at all in mucinous cystic neoplasms (MCNs) (0/10), neuroendocrine neoplasms (0/52), acinar cell neoplasms (0/16), serous cystadenomas (0/10), and solid-pseudopapillary neoplasms (0/14). We found GNAS mutations in 55/91 IPMNs with or without associated invasive carcinoma, solely in intestinal-type (78 %, 21/27) and gastric-type (62 %, 34/55) IPMNs. Of the IPMN-associated adenocarcinomas, mucinous-subtype tumours harboured GNAS mutations more frequently (83 %, 5/6) than tubular-subtype tumours (25 %, 6/24) (p = 0.02). We separately analysed GNAS in the adenocarcinoma and the IPMN component in the IPMN-associated adenocarcinomas. In all mucinous-subtype tumours, the two components exhibited identical genotypes. In contrast, the two components in 8 of 24 tubular-subtype tumours exhibited different genotypes, indicating intratumour heterogeneity. In conclusion, mucinous carcinomas with or without associated IPMN as well as IPMNs frequently harbour a GNAS mutation, reinforcing the notion that these constitute a spectrum of pancreatic tumours. Clinically and pathologically, these tumours are associated, but GNAS mutation sheds further light on this spectrum.

An atypical monomelic presentation of Mazabraud syndrome

Mazabraud syndrome is a rare condition characterized by a combination of fibrous dysplasia and intramuscular myxomas. In Mazabraud syndrome, the distribution of fibrous dysplasia is mostly polyomelic and frequently located in the femur, with myxomas adjacent to the fibrous dysplasia lesion of bone (mostly in the quadriceps muscle). However, when presented as atypical clinical features, patients of Mazabraud syndrome is either misdiagnosed or difficult to diagnose. We report an atypical monomelic case of Mazabraud syndrome in the right upper arm and discuss the difficulties in making an accurate diagnosis.

Intramuscular myxoma of the buttock mimicking low-grade fibromyxoid sarcoma: diagnostic usefulness of MUC4 expression

Intramuscular myxoma (IM) is a benign intramuscular neoplasm composed of fibroblasts and abundant myxoid stroma. Some malignant soft tissue tumors can undergo myxomatous degeneration, which makes it difficult to distinguish them from IM. We describe a case of IM of the buttock region mimicking low-grade fibromyxoid sarcoma. The tumor appeared as a well-defined ovoid mass with a cystic lesion on MRI images, and mild uptake on PET images was seen. This was originally misdiagnosed as low-grade fibromyxoid sarcoma (LGFMS) after core-needle biopsy. The mass was excised en bloc and sent for histology. The surgical specimen showed the features of LGFMS with the same characteristics as those mentioned in the previous biopsy report. After surgery, MUC4 expression, a highly sensitive and specific immunohistochemical marker for LGFMS, and FUS gene rearrangement by FISH was not detected upon re-examination; therefore, a conclusive diagnosis of IM was made. The patient had no local recurrence at the 3-year follow-up. Our case suggests that IM with mild FDG uptake is frequently confused with other low-grade malignant myxoid tumors. In addition, absence of MUC4 expression is the definitive key to distinguish IM from LGFMS.

Diagnostic value of investigating GNAS mutations in fibro-osseous lesions: a retrospective study of 91 cases of fibrous dysplasia and 40 other fibro-osseous lesions

GNAS (guanine nucleotide-binding protein/α-subunit) mutations that induce the activation of G-protein α-subunit participate in the pathogenesis of fibrous dysplasia. The aim of this study was to evaluate the sensitivity and specificity of GNAS mutations in fibrous dysplasia and other fibro-osseous lesions, to assess the value of investigating this mutation in the diagnosis of fibro-osseous lesions. We studied 91 cases of fibrous dysplasia. The quality and/or quantity of genomic DNA were suitable for molecular analysis for 51 cases of fibrous dysplasia. GNAS mutations were investigated by three techniques: high-resolution melting (exon 8), allele-specific PCR (exons 8 and 9) and/or direct DNA sequencing (exons 8 and 9). Fibrous dysplasia samples were classified blind to the GNAS mutation status into six histological subtypes as conventional, fibro-involutive, osteosclerosing, cementifying, osteocartilaginous and with prominent aneurysmal cystic changes. We also studied 14 cases of low-grade osteosarcoma, 21 cases of ossifying fibroma, 3 cases of osteofibrous dysplasia, 1 case of osseous dysplasia of the jawbone and 1 post-traumatic lesion of the ribs. Twenty-three cases of fibrous dysplasia (45%) showed mutations of codon 201 (exon 8, p.R201H or p.R201C). No mutation was found on codon 227 (exon 9). GNAS mutations in conventional fibrous dysplasia were detected in the same proportion (47%) as in the other histological subtypes (47%, P=0.96), regardless of sex (P=0.44), age (P=0.90) and location (P=1). GNAS mutations were not detected in any other fibro-osseous lesions. The GNAS mutation was thus specific to fibrous dysplasia in the context of fibro-osseous lesions. The particular mosaicism of mutant and non-mutant cells within the lesion or the existence of other mutations not already described could explain the lack of GNAS mutation in cases of fibrous dysplasia. Investigating this mutation may constitute a valuable complementary diagnostic tool, despite its low sensitivity, particularly in unconventional morphologically different subtypes of fibrous dysplasia.

Mazabraud's syndrome: case report and literature review

Mazabraud's syndrome is a rare disorder characterized by the association of single or multiple intramuscular myxomas with fibrous dysplasia. Here, we present the first case of Mazabraud's syndrome visualized on 18F-FDG PET/CT with histopathological confirmation of the myxoma. Our case demonstrates a slightly increased FDG uptake (SUVmax 2.1) within the myxomas and a moderately to highly increased tracer uptake (SUVmax 7.0) within the fibrous dysplastic lesions. The typical histological appearance of the intramuscular myxoma confirmed the radiological diagnosis. Further, we discuss the imaging findings and the histopathological features of this rare case with a review of the related literature.

[Intramuscular myxoma of the lower leg]

The intramuscular myxoma is a rare benign soft tissue tumor characterized by bland spindle-shaped and stellate cells embedded in hypovascular myxoid stroma. We report the isolated case of a 44-year-old female patient with an intramuscular myxoma in the anterior tibial muscle and report the clinical and radiographic findings. We performed an analysis of the GNAS gene mutation status with a positive finding. In difficult cases, recurrent tumors or small biopsies detection of a GNAS mutation can be useful to confirm the diagnosis of an intramuscular myxoma.

Molecular pathology and its diagnostic use in bone tumors

Bone tumors are considered by most pathologists difficult to diagnose as they are rare, have overlapping morphology, need radiological correlation, and the usefulness of immunohistochemistry is limited, making conventional morphology the cornerstone of the diagnosis. Over the past decade, more and more has become known of the molecular background of bone tumors. Three groups of bone tumors are recognized, namely, tumors with specific translocations combined with a relatively simple karyotype involving chromosomal translocations (Ewing sarcoma, aneurysmal bone cyst), tumors with specific gene mutations or amplifications (chondrosarcoma, fibrous dysplasia, chordoma), and sarcomas with genetic instability and as a consequence complex karyotypes (osteosarcoma). Technical advancements will rapidly reveal new alterations in the more rare sarcoma subtypes for which the molecular background has remained enigmatic. Opening the archives and using new technologies, as well as refinement of existing technologies for decalcified paraffin-embedded tissue, may bring to light more specific genetic aberrations in bone tumors that can be applied in molecular diagnostics in the near future.

FDG PET/CT and MR imaging of intramuscular myxoma in the gluteus maximus

Intramuscular myxoma is a rare benign soft tissue tumor which may be mistaken for other benign and low-grade malignant myxoid neoplasms. We present the case of a 63-year-old woman with an asymptomatic intramuscular myxoma discovered incidentally on a whole-body F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography. PET images showed a mild FDG uptake (maximum standardized uptake value, 1.78) in the left gluteus maximus. Subsequent magnetic resonance (MR) imaging revealed a well-defined ovoid mass with homogenous low signal intensity on T1-weighted sequences and markedly high signal intensity on T2-weighted sequences. Contrast-enhanced MR images showed heterogeneous enhancement throughout the mass. The diagnosis of intramuscular myxoma was confirmed on histopathology after surgical excision of the tumor. The patient had no local recurrence at one year follow-up. Our case suggests that intramuscular myxoma should be considered in the differential diagnosis of an oval-shaped intramuscular soft tissue mass with a mild FDG uptake.

Myxomatous corneal degeneration: a clinicopathological study of six cases and a review of the literature

Thirteen cases with myxomatous changes of the corneal stroma have been reported to date. We report six additional cases with clinical, histopathological, and immunohistochemical data. The clinical appearance is most often a gelatinous, whitish elevation with insidious onset. Histopathologically, there are inconspicuous spindle- and stellate-shaped cells in a loose, myxoid matrix. The typical location is in the anterior cornea beneath the epithelium, with varying degrees of extension into the stroma. Vimentin and smooth-muscle actin immunohistochemical stains are characteristically positive, and staining occasionally may be seen with muscle-specific actin, whereas CD34 staining usually is negative. In most cases, myxomatous changes are a degenerative process involving transformation of stromal keratocytes into cells with prominent secretory activity and myofibroblastic differentiation. Most occur in corneas with a history of ocular disease or trauma that disrupts Bowman's layer. We suggest labelling lesions with these features as "myxomatous corneal degeneration." So-called "primary corneal myxomas" also exist where there is no significant history. It remains unclear whether the myxomatous changes in such lesions are neoplastic or degenerative. Myxomatous corneal changes are likely under-recognized and under-diagnosed.

Fibrous dysplasia of bone associated with soft-tissue myxomas as well as an intra-osseous myxoma in a woman with Mazabraud's syndrome: a case report

Introduction

Mazabraud's syndrome is a rare but well-described disorder characterized by fibrous dysplasia in single or multiple bones associated with one or more soft-tissue myxomas. In this report, we describe what is, to the best of our knowledge, the first case involving an intra-osseous myxoma. This finding supports, and could provide new insight into, the pathological association between fibrous dysplasia and myxomas.

Case presentation

In this report, we describe the case of a 49-year-old Caucasian woman known for years to have fibrous dysplasia in the left femur and tibia who presented with progressive pain in her left leg and soft swelling in the left quadriceps region. After surgical intervention with excision of the soft-tissue mass, the diagnosis of Mazabraud's syndrome was confirmed. During follow-up, our patient presented with a painless mass located on the lateral side of the left knee, next to a second, intra-osseous lesion with the same characteristics in the left lateral tibial plateau. The histopathological examination was consistent with a soft-tissue intra-osseous myxoma.

Conclusion

In the international literature, 67 cases of Mazabraud's syndrome have been described so far.

To our knowledge, the present case report is the first to describe the combination of polyostotic fibrous dysplasia and intra-muscular as well as intra-osseous myxoma.

Benefits of molecular pathology in the diagnosis of musculoskeletal disease : Part II of a two-part review: bone tumors and metabolic disorders

The second part of this review, on the benefits of molecular pathology in the diagnosis disease, focuses on the genetics of bone tumors and metabolic disease. Unlike soft tissue tumors, the number of currently exploitable molecular abnormalities for diagnosing bone neoplasms is small, although the same gene rearrangements are found in primitive neuroectodermal tumor/Ewing sarcoma in both skeletal and extraskeletal sites. Compared with soft tissue tumors, genetic abnormalities, which are valuable to diagnosticians in skeletal disease, are often germline and post-zygotic aberrations rather than somatic translocations. In addition, the review highlights the range of disease entities classified as "osteoclast-rich lesions," some of which harbor germline mutations. It also addresses the importance of phosphate metabolism in skeletal disorders including phosphaturic mesenchymal tumor, vitamin D-resistant rickets, and tumoral calcinosis.

Molecular pathology of sarcomas: concepts and clinical implications

The molecular genetic changes that have been described in sarcomas over the past era have aided our understanding of their pathogenesis. The majority of sarcomas carry nonspecific genetic changes within a background of a complex karyotype. These constitute the challenges in sarcoma research for unraveling a putative multistep genetic model, such as for chondrosarcoma, and finding targets for therapeutic strategies. Approximately 15-20% of mesenchymal tumors carry a specific translocation within a relatively simple karyotype. The resulting fusion products act either as transcription factors upregulating genes responsible for tumor growth, as for instance in Ewing sarcoma, or translocate a highly active promoter in front of an oncogene driving tumor formation, as for instance in aneurysmal bone cyst. In addition, a small subset of mesenchymal tumors have specific somatic mutations driving oncogenesis. The specific genetic changes unraveled so far had great impact on the classification of bone and soft tissue tumors. In addition, these changes can assist the pathologist in the differential diagnosis of some of these entities, especially within the groups of small blue round cell tumors and spindle cell tumors, if performed in specialized centers. While a putative association between certain fusion products and outcome is still under debate, the role of predicting response of targeted therapy has been well established for KIT and PDGFRA mutations in gastrointestinal stromal tumors.

GNAS1 mutations occur more commonly than previously thought in intramuscular myxoma

Mutation detection plays an important role in diagnostic pathology, not only in providing a tissue diagnosis, but also in predicting response to antitumourigenic agents. However, mutation detection strategies are often hampered by masking of mutant alleles by wild-type sequences. Coamplification at lower denaturation temperature PCR (COLD-PCR) reportedly increases the proportion of rare variant sequences in a wild-type background by using PCR cycles in which the denaturation temperature is reduced to favour product formation with lower melt temperatures and heteroduplexes arising from minor variants. Intramuscular myxoma is a rare benign soft tissue neoplasm that occurs sporadically and less commonly in association with fibrous dysplasia (Mazabraud's syndrome). Fibrous dysplasia results from activating GNAS1 mutations, and the same mutations have been identified in small numbers of intramuscular myxoma. The aim of the study was primarily to establish whether COLD-PCR is more sensitive than conventional PCR; this was achieved by testing for GNAS1 mutations in intramuscular myxomas using the two methodologies. Mutations were detected in 8 of 28 (29%) cases of intramuscular myxomas using conventional PCR followed by mutation-specific restriction enzyme digestion (PCR-MSRED) whereas 17 of 28 (61%) mutations were detected using COLD-PCR/MSRED. Mutations were detected in two cases where a diagnosis of low-grade myxofibrosarcoma had been favoured over intramuscular myxoma. No mutations were detected in an additional 9 low-grade and 19 high-grade myxofibrosarcomas, and another 40 control samples. This study shows the power of COLD-PCR compared with conventional PCR in mutation detection, and shows that GNAS1 mutation detection increases diagnostic accuracy when distinguishing between intramuscular myxoma and low-grade myxofibrosarcoma.

Cellular/intramuscular myxoma and grade I myxofibrosarcoma are characterized by distinct genetic alterations and specific composition of their extracellular matrix

Cellular myxoma and grade I myxofibrosarcoma are mesenchymal tumours that are characterized by their abundant myxoid extracellular matrix (ECM). Despite their histological overlap, they differ clinically. Diagnosis is therefore difficult though important. We investigated their (cyto) genetics and ECM. GNAS1-activating mutations have been described in intramuscular myxoma, and lead to downstream activation of cFos. KRAS and TP53 mutations are commonly involved in sarcomagenesis whereby KRAS subsequently activates c-Fos. A well-documented series of intramuscular myxoma (three typical cases and seven cases of the more challenging cellular variant) and grade I myxofibrosarcoma (n= 10) cases were karyotyped, analyzed for GNAS1, KRAS and TP53 mutations and downstream activation of c-Fos mRNA and protein expression. ECM was studied by liquid chromatography mass spectrometry and expression of proteins identified was validated by immunohistochemistry and qPCR. Grade I myxofibrosarcoma showed variable, non-specific cyto-genetic aberrations in 83,5% of cases (n= 6) whereas karyotypes of intramuscular myxoma were all normal (n= 7). GNAS1-activating mutations were exclusively found in 50% of intramuscular myxoma. Both tumour types showed over-expression of c-Fos mRNA and protein. No mutations in KRAS codon 12/13 or in TP53 were detected. Liquid chromatography mass spectrometry revealed structural proteins (collagen types I, VI, XII, XIV and decorin) in grade I myxofibrosarcoma lacking in intramuscular myxoma. This was confirmed by immunohistochemistry and qPCR. Intramuscular/cellular myxoma and grade I myxofibrosarcoma show different molecular genetic aberrations and different composition of their ECM that probably contribute to their diverse clinical behaviour. GNAS1 mutation analysis can be helpful to distinguish intramuscular myxoma from grade I myxofibrosarcoma in selected cases.

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

AIMS

To report on the mutation-specific restriction enzyme digest (MSRED) method using paraffin-embedded tissue as a means of detecting GNAS1 mutations in fibrous dysplasia (FD), and to determine if any of the reported GNAS1 mutations in endocrine neoplasms, not previously documented in FD, can be found in FD.

METHODS AND RESULTS

Sixty-seven cases of extragnathic FD were analysed as two groups, 1997-2002 and 2003-06, chosen because tissue fixation and decalcification methods were more accurately recorded in the latter. MSRED revealed that between 2003 and 2006, 93% of 28 'in house' extragnathic cases harboured a GNAS1 mutation, compared with 75% of 32 cases before 2003. Fixation times of no more than 48 h and decalcification in ethylenediamine tetraacetic acid gave the best results. Of the 56 mutations detected (five gnathic, 51 extragnathic), 32 (57%) were R201H, 21 (38%) were R201C and three (5%) were Q227L. Two Q227L extragnathic cases had unusual clinical/radiological findings. No mutations were detected in osteofibrous dysplasia.

CONCLUSION

Detection of GNAS1 mutations by MSRED is a valuable adjunct to the histopathological diagnosis of FD. This is the first report of a Q227L mutation in FD, although it has been previously documented in pituitary adenoma.

Solitary intramuscular myxoma with monostotic fibrous dysplasia as a rare variant of Mazabraud's syndrome

The rare coexistence of intramuscular myxoma (IM) and fibrous dysplasia (FD) is known as Mazabraud's syndrome. IM tends to occur multifocally and is associated most frequently with polyostotic FD in Mazabraud's syndrome. We present an extremely rare combination of a solitary IM and monostotic FD as a variant of Mazabraud's syndrome, and discuss the importance of recognizing this rare coexistence for appropriate management of the patient.

G(s)alpha mutations in fibrous dysplasia and McCune-Albright syndrome

Fibrous dysplasia (FD) is a focal bone lesion composed of immature mesenchymal osteoblastic precursor cells. Some FD patients also have hyperpigmented skin lesions (café-au-lait spots), gonadotropin-independent sexual precocity, and/or other endocrine and nonendocrine manifestations (McCune-Albright syndrome [MAS]). MAS results from somatic mutations occurring during early development, resulting in a widespread mosaic of normal and mutant-bearing cells, which predicts that the clinical presentation of each patient is determined by the extent and distribution of abnormal cells. These mutations encode constitutively active forms of G(s)alpha, the ubiquitously expressed G protein alpha-subunit that couples hormone receptors to intracellular cAMP generation. These mutations lead to substitution of amino acid residues that are critical for the intrinsic GTPase activity that is normally required to deactivate the G protein. This leads to prolonged activation of G(s)alpha and its downstream effectors even with minimal receptor activation. This explains why MAS patients have stimulation of multiple peripheral endocrine glands in the absence of circulating stimulatory pituitary hormones and increased skin pigment, which is normally induced by melanocyte-stimulating hormone through G(s)alpha/cAMP. Similar mutations are also present in 40% of pituitary tumors in acromegaly patients and less commonly in other endocrine tumors. FD results from increased cAMP in bone marrow stromal cells, leading to increased proliferation and abnormal differentiation. Parental origin of the mutated allele may also affect the clinical presentation, because G(s)alpha is imprinted and expressed only from the maternal allele in some tissues (e.g., pituitary somatotrophs).