Is total-body MRI useful as a screening tool to rule out malignant progression in patients with multiple osteochondromas? Results in a single-center cohort of 319 adult patients

PURPOSE

To evaluate the results of total-body (TB) MRI used as a screening tool for assessment or exclusion of malignant transformation in patients with hereditary multiple osteochondromas (HMO).

PATIENTS AND METHODS

In a single-institute cohort of MO patients, 366 TB-MRI examinations, including T1-weighted and STIR images, were performed for screening and follow-up purposes to rule out the malignant transformation, and retrospectively analyzed. In each patient, the presence and location of osteochondromas in the axial and appendicular bones were recorded. Forty-seven patients underwent a second TB surveillance in this period. STIR sequences were used to identify sites of increased signal intensity that could represent suspicious thickened cartilage caps or indeterminate reactive changes related to osteochondromas.

RESULTS

In 82% of patients, one or more OC locations were determined in one or more flat bones. In 366 exams, nine OC (2,5 %) with suspicious imaging features were identified. These proved to be peripheral chondrosarcomas after targeted MRI and resection were performed. All nine malignant lesions were in flat bones (pelvis 5, ribs 3, scapula 1). Three of these patients were 19 years of age. In 12 patients who had peripheral or intraosseous low-grade chondrosarcoma in their history, before their first TB-MRI, no new lesions were identified. Twenty-three additional TB-MRI exams, demonstrating focal high T2 signal intensity, also gave rise to performing additional targeted MRI. One OC of the distal femur was excised and appeared benign. No suspicious cartilage caps were depicted on the remaining 22 targeted MRI exams but instead increased T2 signal was clarified by reactive changes (frictional bursitis, soft tissue edema) in close relation with benign osteochondromas. No malignant lesions were found in 47 patients who had a second TB surveillance (mean interval between exams 3.2 years, range 2-5 years).

CONCLUSION

TB-MRI can identify malignant transformation of osteochondromas in HMO patients. All peripheral chondrosarcomas occurred in flat bones (ribs, scapula, pelvis) in our study. TB-MRI might assist in triage between higher risk patients with a high burden of OC, including the location of OC in main flat bones vs lower risk patients without OC of the flat bones.

Osteochondroma formation is independent of heparanase expression as revealed in a mouse model of hereditary multiple exostoses

Hereditary multiple exostoses (HME) is a rare, pediatric disorder characterized by osteochondromas that form along growth plates and provoke significant musculoskeletal problems. HME is caused by mutations in heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2. Seemingly paradoxically, osteochondromas were found to contain excessive extracellular heparanase (Hpse) that could further reduce HS levels and exacerbate pathogenesis. To test Hpse roles, we asked whether its ablation would protect against osteochondroma formation in a conditional HME model consisting of mice bearing floxed Ext1 alleles in Agr-CreER background (Ext1f/f ;Agr-CreER mice). Mice were crossed with a new global Hpse-null (Hpse-/- ) mice to produce compound Hpse-/- ;Ext1f/f ;Agr-CreER mice. Tamoxifen injection of standard juvenile Ext1f/f ;Agr-CreER mice elicited stochastic Ext1 ablation in growth plate and perichondrium, followed by osteochondroma formation, as revealed by microcomputed tomography and histochemistry. When we examined companion conditional Ext1-deficient mice lacking Hpse also, we detected no major decreases in osteochondroma number, skeletal distribution, and overall structure by the analytical criteria above. The Ext1 mutants used here closely mimic human HME pathogenesis, but have not been previously tested for responsiveness to treatments. To exclude some innate therapeutic resistance in this stochastic model, tamoxifen-injected Ext1f/f ;Agr-CreER mice were administered daily doses of the retinoid Palovarotene, previously shown to prevent ectopic cartilage and bone formation in other mouse disease models. This treatment did inhibit osteochondroma formation compared with vehicle-treated mice. Our data indicate that heparanase is not a major factor in osteochondroma initiation and accumulation in mice. Possible roles of heparanase upregulation in disease severity in patients are discussed.

Total hip arthroplasty in hereditary multiple exostoses with secondary osteoarthritis: A case report

RATIONALE

Hereditary multiple exostoses (HME) is an autosomal dominant disease that causes multiple exostoses throughout the body. It usually occurs around the metaphysis of the long bones, and when it involves the hip, symptoms arise due to deformity and the mass effect. If the lesion does not involve the joint or is not associated with arthritis, symptoms can be relieved by surgical excision of the osteochondroma. However, if secondary osteoarthritis (OA) or subluxation of the joint has progressed, joint replacement arthroplasty should be considered.

PATIENT CONCERNS

A 57-year-old woman with HME visited our outpatient department with severe right hip pain. She complained of difficulty walking and severe discomfort during activities of daily living. She was short in stature and had a family history of HME.

DIAGNOSIS

A physical examination revealed limited motion in the hip joint and a limb length discrepancy. Plain radiography and a computed tomography scan revealed huge osteochondromas on bilateral proximal femurs and advanced OA with subluxation of the right hip joint.

INTERVENTIONS

Cementless total hip arthroplasty of the right hip joint via the modified posterolateral approach was done.

OUTCOMES

The patient showed good clinical scores and functional improvement at the 2-year follow-up.

LESSONS

Total hip arthroplasty for an anatomically deformed joint is technically difficult, and there are many factors to consider that can make surgeons reluctant to use this modality. However, with careful preparation, arthroplasty is a good surgical option for symptomatic and functional recovery in HME patients with hip joint involvement.

Signaling systems affecting the severity of multiple osteochondromas

Multiple osteochondromas (MO) syndrome is a dominant autosomal bone disorder characterized by the formation of cartilage-capped bony outgrowths that develop at the juxtaposition of the growth plate of endochondral bones. MO has been linked to mutations in either EXT1 or EXT2, two glycosyltransferases required for the synthesis of heparan sulfate (HS). The establishment of mouse mutants demonstrated that a clonal, homozygous loss of Ext1 in a wild type background leads to the development of osteochondromas. Here we investigate mechanisms that might contribute to the variation in the severity of the disease observed in human patients. Our results show that residual amounts of HS are sufficient to prevent the development of osteochondromas strongly supporting that loss of heterozygosity is required for osteochondroma formation. Furthermore, we demonstrate that different signaling pathways affect size and frequency of the osteochondromas thereby modulating the severity of the disease. Reduced Fgfr3 signaling, which regulates proliferation and differentiation of chondrocytes, increases osteochondroma number, while activated Fgfr3 signaling reduces osteochondroma size. Both, activation and reduction of Wnt/β-catenin signaling decrease osteochondroma size and frequency by interfering with the chondrogenic fate of the mutant cells. Reduced Ihh signaling does not change the development of the osteochondromas, while elevated Ihh signaling increases the cellularity and inhibits chondrocyte differentiation in a subset of osteochondromas and might thus predispose osteochondromas to the transformation into chondrosarcomas.

Heterotopic Ossification of the Xiphoid Process after Abdominal Surgery for Traumatic Hemoperitoneum

Heterotopic ossification of the xiphoid process is extremely rare, with only three cases previously reported. However, the surgical pathology for postoperative elongation of the xiphoid process after abdominal surgery has not yet been reported. We report a case of the postoperative elongation of the xiphoid process, 8 years after abdominal surgery for traumatic hemoperitoneum in a 53-year-old man. The patient underwent surgical excision of the elongated mass of the xiphoid process. Histopathology revealed multiple exostoses. Heterotopic ossification can occur after surgical trauma to soft or bone tissue. Surgical excision with primary closure is the treatment of choice for symptomatic heterotopic ossification.

Chondrosarcoma in Metachondromatosis: A Rare Case Report

Metachondromatosis which was first described in 1971 by Maroteaux is a rare genetic disease consisting of osteochondromas and enchondromas, caused by loss of function of the PTPN11 gene. It is distinct from other cartilaginous tumors such as multiple osteochondromas and hereditary multiple exostosis by the distribution and orientation of lesions, and pattern of inheritance. In Metachondromatosis osteochondromas typically occur in hands, feet, femur, and tibia while enchondromas commonly affect the pelvic bones and femurs. Both tumors are generally reported to regress in adulthood. To the best of our knowledge only one case of Chondrosarcoma has been reported, and our case is the second reported case of Chondrosarcoma in metachondromatosis.

Unsuspected osteochondroma-like outgrowths in the cranial base of Hereditary Multiple Exostoses patients and modeling and treatment with a BMP antagonist in mice

Hereditary Multiple Exostoses (HME) is a rare pediatric disorder caused by loss-of-function mutations in the genes encoding the heparan sulfate (HS)-synthesizing enzymes EXT1 or EXT2. HME is characterized by formation of cartilaginous outgrowths-called osteochondromas- next to the growth plates of many axial and appendicular skeletal elements. Surprisingly, it is not known whether such tumors also form in endochondral elements of the craniofacial skeleton. Here, we carried out a retrospective analysis of cervical spine MRI and CT scans from 50 consecutive HME patients that included cranial skeletal images. Interestingly, nearly half of the patients displayed moderate defects or osteochondroma-like outgrowths in the cranial base and specifically in the clivus. In good correlation, osteochondromas developed in the cranial base of mutant Ext1f/f;Col2-CreER or Ext1f/f;Aggrecan-CreER mouse models of HME along the synchondrosis growth plates. Osteochondroma formation was preceded by phenotypic alteration of cells at the chondro-perichondrial boundary and was accompanied by ectopic expression of major cartilage matrix genes -collagen 2 and collagen X- within the growing ectopic masses. Because chondrogenesis requires bone morphogenetic protein (BMP) signaling, we asked whether osteochondroma formation could be blocked by a BMP signaling antagonist. Systemic administration with LDN-193189 effectively inhibited osteochondroma growth in conditional Ext1-mutant mice. In vitro studies with mouse embryo chondrogenic cells clarified the mechanisms of LDN-193189 action that turned out to include decreases in canonical BMP signaling pSMAD1/5/8 effectors but interestingly, concurrent increases in such anti-chondrogenic mechanisms as pERK1/2 and Chordin, Fgf9 and Fgf18 expression. Our study is the first to reveal that the cranial base can be affected in patients with HME and that osteochondroma formation is amenable to therapeutic drug intervention.

Multiple Skeletal Deformities in a Middle-Aged Man

A 54-year-old man was seen in our endocrinology clinic with evidence of a limited range of motion in his left foot. He had a history of diabetes mellitus type 2 and atrial fibrillation. His family history included evidence of skeletal deformities in some of his relatives. This could imply the potential existence of a hereditary condition. It is worth noting that spontaneous mutations have been reported in some cases. A pertinent physical examination revealed a surgical scar on the patient's left knee, a hallux valgus deformity on his left foot with compromised joint function, and painless bony prominences on that same foot. The skeletal survey findings were consistent with multiple hereditary exostoses. Multiple osteochondromatosis (MO) is a rare genetic disorder associated with serious complications that may significantly affect the health related quality of life of anyone having the disorder. To prevent further complications, these patients require long-term follow-up with regular clinical and radiological examinations.

Carriers of loss-of-function mutations in EXT display impaired pancreatic beta-cell reserve due to smaller pancreas volume

Exotosin (EXT) proteins are involved in the chain elongation step of heparan sulfate (HS) biosynthesis, which is intricately involved in organ development. Loss of function mutations (LOF) in EXT1 and EXT2 result in hereditary exostoses (HME). Interestingly, HS plays a role in pancreas development and beta-cell function, and genetic variations in EXT2 are associated with an increased risk for type 2 diabetes mellitus. We hypothesized that loss of function of EXT1 or EXT2 in subjects with hereditary multiple exostoses (HME) affects pancreatic insulin secretion capacity and development. We performed an oral glucose tolerance test (OGTT) followed by hyperglycemic clamps to investigate first-phase glucose-stimulated insulin secretion (GSIS) in HME patients and age and gender matched non-affected relatives. Pancreas volume was assessed with magnetic resonance imaging (MRI). OGTT did not reveal significant differences in glucose disposal, but there was a markedly lower GSIS in HME subjects during hyperglycemic clamp (iAUC HME: 0.72 [0.46–1.16] vs. controls 1.53 [0.69–3.36] nmol·l⁻¹·min⁻¹, p<0.05). Maximal insulin response following arginine challenge was also significantly attenuated (iAUC HME: 7.14 [4.22–10.5] vs. controls 10.2 [7.91–12.70] nmol·l⁻¹·min⁻¹ p<0.05), indicative of an impaired beta-cell reserve. MRI revealed a significantly smaller pancreatic volume in HME subjects (HME: 72.0±15.8 vs. controls 96.5±26.0 cm³ p = 0.04). In conclusion, loss of function of EXT proteins may affect beta-cell mass and insulin secretion capacity in humans, and render subjects at a higher risk of developing type 2 diabetes when exposed to environmental risk factors.

Multiple cartilaginous exostoses and development of chondrosarcomas--a systematic review

INTRODUCTION

Hereditary multiple cartilaginous exostoses is a syndrome characterised by the development of multiple osteochondromas. The diagnosis is typically made around the age of 12 years, and the prevalence is estimated at 1:50,000. During skeletal growth, the osteochondromas are benign, but in adult life malignant transformation into chondrosarcomas can occur.

METHODS

This study was a literature survey based on a systematic search of the PubMed database for articles with the term "hereditary multiple exostoses chondrosarcoma". The search returned 157 articles, of which 13 had a sufficient level of evidence. These publications were examined thoroughly, focusing on the development of sarcomas, symptoms and the risk of malignant degeneration.

RESULTS

There is no consensus regarding the frequency of malignant transformation of multiple cartilaginous exostoses into sarcomas, which varies from less than 1% to 25%. The most reliable estimation seems to be 1-2%. The survey of the literature shows that no risk groups can be identified. However, exostoses in the axial skeleton are more prone to develop into chondrosarcomas than peripheral exostoses.

CONCLUSION

It is indisputable that malignant transformation occurs, and we therefore propose that a follow-up programme be launched with clinical examination by magnetic resonance imaging or bone scintigraphy every second year. The purpose of such programme would be to discover the sarcomatous development as early as possible to improve the survival prognosis of the patients. This screening programme should be centralised at tumour departments.

SHP2 regulates chondrocyte terminal differentiation, growth plate architecture and skeletal cell fates

Loss of PTPN11/SHP2 in mice or in human metachondromatosis (MC) patients causes benign cartilage tumors on the bone surface (exostoses) and within bones (enchondromas). To elucidate the mechanisms underlying cartilage tumor formation, we investigated the role of SHP2 in the specification, maturation and organization of chondrocytes. Firstly, we studied chondrocyte maturation by performing RNA-seq on primary chondrocyte pellet cultures. We found that SHP2 depletion, or inhibition of the ERK1/2 pathway, delays the terminal differentiation of chondrocytes from the early-hypertrophic to the late-hypertrophic stage. Secondly, we studied chondrocyte maturation and organization in mice with a mosaic postnatal inactivation of Ptpn11 in chondrocytes. We found that the vertebral growth plates of these mice have expanded domains of early-hypertrophic chondrocytes that have not yet terminally differentiated, and their enchondroma-like lesions arise from chondrocytes displaced from the growth plate due to a disruption in the organization of maturation and ossification zones. Furthermore, we observed that lesions from human MC patients also display disorganized chondrocyte maturation zones. Next, we found that inactivation of Ptpn11 in Fsp1-Cre-expressing fibroblasts induces exostosis-like outgrowths, suggesting that loss of SHP2 in cells on the bone surface and at bone-ligament attachment sites induces ectopic chondrogenesis. Finally, we performed lineage tracing to show that exostoses and enchondromas in mice likely contain mixtures of wild-type and SHP2-deficient chondrocytes. Together, these data indicate that in patients with MC, who are heterozygous for inherited PTPN11 loss-of-function mutations, second-hit mutations in PTPN11 can induce enchondromas by disrupting the organization and delaying the terminal differentiation of growth plate chondrocytes, and can induce exostoses by causing ectopic chondrogenesis of cells on the bone surface. Furthermore, the data are consistent with paracrine signaling from SHP2-deficient cells causing SHP2-sufficient cells to be incorporated into the lesions.

Patients with the inherited disorder, metachondromatosis (MC), develop multiple benign cartilage tumors during childhood. MC patients carry heterozygous loss-of-function mutations in the PTPN11 gene, and their cartilage tumors likely arise when the second PTPN11 allele is lost due to a somatic mutation. PTPN11 encodes a phosphatase called SHP2 that is involved in a variety of signaling pathways. Here, we use mouse models and cell culture assays to investigate the mechanisms by which loss of SHP2 promotes cartilage tumor formation. We show that cartilage tumors that form inside bones (enchondromas) likely arise due to disorganized growth and delayed terminal differentiation of growth plate chondrocytes, while cartilage tumors that form on the bone surface (exostoses) can arise due to ectopic chondrogenesis of fibroblast-like cells that surround bones. We also suggest that paracrine signals from SHP2-deficient cells cause neighboring SHP2-sufficient cells to contribute to exostoses and enchondromas. Finally, we provide in vitro data that the ERK1/2 pathway is regulated by SHP2 and promotes chondrocyte terminal differentiation. Together, our data provide insight into the mechanisms underlying cartilage tumor formation and implicate SHP2 as a key regulator of chondrocyte specification, organization and maturation.

Targeted disruption of Shp2 in chondrocytes leads to metachondromatosis with multiple cartilaginous protrusions

Metachondromatosis is a benign bone disease predominantly observed in the hands and feet of children or young adults demonstrating two different manifestations: a cartilage-capped bony outgrowth on the surface of the bone called exostosis and ectopic cartilaginous nodules inside the bone called enchondroma. Recently, it has been reported that loss-of-function mutations of the SHP2 gene, which encodes the SHP2 protein tyrosine phosphatase, are associated with metachondromatosis. The purpose of this study was to investigate the role of SHP2 in postnatal cartilage development, which is largely unknown. We disrupted Shp2 during the postnatal stage of mouse development in a chondrocyte-specific manner using a tamoxifen-inducible system. We found tumor-like nodules on the hands and feet within a month after the initial induction. The SHP2-deficient mice demonstrated an exostosis-like and enchondroma-like phenotype in multiple bones of the hands, feet, and ribs as assessed by X-ray and micro-computed tomography (CT). Histological assessment revealed the disorganization of the growth plate cartilage, a cartilaginous protrusion from the epiphyseal bone, and ectopic cartilage nodules within the bones, which is consistent with the pathological features of metachondromatosis in humans (ie, both exostosis and enchondroma). At molecular levels, we observed an abundant expression of Indian hedgehog protein (IHH) and fibroblast growth factor 2 (FGF2) and impaired expression of mitogen-activated protein kinases (MAPK) in the affected cartilage nodules in the SHP2-deficient mice. In summary, we have generated a mouse model of metachondromatosis that includes manifestations of exostosis and enchondroma. This study provides a novel model for the investigation of the pathophysiology of the disease and advances the understanding of metachondromatosis. This model will be useful to identify molecular mechanisms for the disease cause and progression as well as to develop new therapeutic strategies in the future.

Morphological classification for prediction of malignant transformation in multiple exostoses

AIM

To explore the value of morphological classification in predicting malignant transformation in multiple exostoses (ME).

PATIENTS AND METHODS

The imaging data of 116 patients (totally 190 tumors) with ME were retrospectively analyzed. All the tumors were pathology confirmed after surgical resection, including 175 exostoses from 101 patients, and 15 exostotic chondrosarcomas in 15 cases. Based on the ratio of diameter between tumor tip and tumor base (R1), tumors were classified into two types: cauliflower-like tumor (R1 ≥ 1.0) and non-cauliflower-like tumor (R1 < 1.0). In addition, non-cauliflower-like tumors were further classified into two subtypes according to the ratio of tumor height to tumor base diameter: sessile type (R2 < 1.0) and pedunculated type (R2 ≥ 1.0). The relationship between tumor shape and malignant transformation was studied.

RESULTS

Of all the 175 exostoses from 101 patients, 27 were cauliflower-like tumors and 148 were non-cauliflower-like tumors. Of all the 15 exostotic chondrosarcomas in 15 cases, most tumors were cauliflower-like (c2 = 38.0075, p < 0.05). Cauliflower-like tumor for the prediction of exostotic chondrosarcoma, the sensibility, specificity, positive predictive value, negative predictive value were 86.7%, 84.6%, 32.5%, 98.7%, respectively.

CONCLUSIONS

Tumor malignant transformation was more common in cauliflower-like tumors than in non-cauliflower-like tumors. The morphological classification and preventive resection of cauliflower-like tumors maybe helpful in preventing the malignant transformation of ME.

Hereditary multiple exostosis

Hereditary multiple exostosis is an intriguing genetic condition with a clinical impact in the field of orthopaedics, paediatrics and oncology. In this review we highlight the current knowledge about this condition from a clinical and scientific point of view. This gives us more insight into the molecular mechanisms and current models on which therapeutic agents are based. It allows for a multidisciplinary approach to the management of this complex condition. There is currently no exact pathological model that can accurately describe all the findings in the research on Hereditary Multiple Exostosis. Promising treatments with blocking agents are currently under investigation.

Ptpn11 deletion in a novel progenitor causes metachondromatosis by inducing hedgehog signalling

The tyrosine phosphatase SHP2, encoded by PTPN11, is required for the survival, proliferation and differentiation of various cell types. Germline activating mutations in PTPN11 cause Noonan syndrome, whereas somatic PTPN11 mutations cause childhood myeloproliferative disease and contribute to some solid tumours. Recently, heterozygous inactivating mutations in PTPN11 were found in metachondromatosis, a rare inherited disorder featuring multiple exostoses, enchondromas, joint destruction and bony deformities. The detailed pathogenesis of this disorder has remained unclear. Here we use a conditional knockout (floxed) Ptpn11 allele (Ptpn11(fl)) and Cre recombinase transgenic mice to delete Ptpn11 specifically in monocytes, macrophages and osteoclasts (lysozyme M-Cre; LysMCre) or in cathepsin K (Ctsk)-expressing cells, previously thought to be osteoclasts. LysMCre;Ptpn11(fl/fl) mice had mild osteopetrosis. Notably, however, CtskCre;Ptpn11(fl/fl) mice developed features very similar to metachondromatosis. Lineage tracing revealed a novel population of CtskCre-expressing cells in the perichondrial groove of Ranvier that display markers and functional properties consistent with mesenchymal progenitors. Chondroid neoplasms arise from these cells and show decreased extracellular signal-regulated kinase (ERK) pathway activation, increased Indian hedgehog (Ihh) and parathyroid hormone-related protein (Pthrp, also known as Pthlh) expression and excessive proliferation. Shp2-deficient chondroprogenitors had decreased fibroblast growth factor-evoked ERK activation and enhanced Ihh and Pthrp expression, whereas fibroblast growth factor receptor (FGFR) or mitogen-activated protein kinase kinase (MEK) inhibitor treatment of chondroid cells increased Ihh and Pthrp expression. Importantly, smoothened inhibitor treatment ameliorated metachondromatosis features in CtskCre;Ptpn11(fl/fl) mice. Thus, in contrast to its pro-oncogenic role in haematopoietic and epithelial cells, Ptpn11 is a tumour suppressor in cartilage, acting through a FGFR/MEK/ERK-dependent pathway in a novel progenitor cell population to prevent excessive Ihh production.

Perichondrium phenotype and border function are regulated by Ext1 and heparan sulfate in developing long bones: a mechanism likely deranged in Hereditary Multiple Exostoses

During limb skeletogenesis the cartilaginous long bone anlagen and their growth plates become delimited by perichondrium with which they interact functionally. Yet, little is known about how, despite being so intimately associated with cartilage, perichondrium acquires and maintains its distinct phenotype and exerts its border function. Because perichondrium becomes deranged and interrupted by cartilaginous outgrowths in Hereditary Multiple Exostoses (HME), a pediatric disorder caused by EXT mutations and consequent heparan sulfate (HS) deficiency, we asked whether EXT genes and HS normally have roles in establishing its phenotype and function. Indeed, conditional Ext1 ablation in perichondrium and lateral chondrocytes flanking the epiphyseal region of mouse embryo long bone anlagen - a region encompassing the groove of Ranvier - caused ectopic cartilage formation. A similar response was observed when HS function was disrupted in long bone anlagen explants by genetic, pharmacological or enzymatic means, a response preceded by ectopic BMP signaling within perichondrium. These treatments also triggered excess chondrogenesis and cartilage nodule formation and overexpression of chondrogenic and matrix genes in limb bud mesenchymal cells in micromass culture. Interestingly, the treatments disrupted the peripheral definition and border of the cartilage nodules in such a way that many nodules overgrew and fused with each other into large amorphous cartilaginous masses. Interference with HS function reduced the physical association and interactions of BMP2 with HS and increased the cell responsiveness to endogenous and exogenous BMP proteins. In sum, Ext genes and HS are needed to establish and maintain perichondrium's phenotype and border function, restrain pro-chondrogenic signaling proteins including BMPs, and restrict chondrogenesis. Alterations in these mechanisms may contribute to exostosis formation in HME, particularly at the expense of regions rich in progenitor cells including the groove of Ranvier.

Giant osteochondroma of axis in a child with multiple hereditary exostoses: case report and review of literature

Though osteochondromas are the most common benign bone tumour, their spinal involvement is less frequent. We report a case of osteochondroma in a 5-year-old female child with multiple hereditary exostoses that originated from posterior elements of C2 vertebra, not involving spinal canal and caused restriction of neck movement. It was excised from its base without disturbing the continuity of lamina. Two years later she had normal neck movements without any recurrence. The rarity of this tumour at this location, with such a large size at an early age, makes this article unique.

Similar cytogenetic findings in two synchronous secondary peripheral chondrosarcomas in a patient with multiple osteochondromas

Secondary peripheral chondrosarcoma is a malignant chondroid tumor arising in a benign precursor, either an osteochondroma or an enchondroma. Multiple osteochondromas syndrome (MO) is an autosomal dominant skeletal disorder associated with bony growths in the form of osteochondromas that occasionally undergo malignant transformation to secondary peripheral chondrosarcomas. We describe the genetic examination of three secondary peripheral chondrosarcomas that had arisen synchronously from osteochondromas in a patient with MO by chromosome banding, high resolution chromosomal comparative genomic hybridization, and mutation analysis of the EXT1 and EXT2 genes. In two of the tumors (the third was not genetically informative), very similar chromosome abnormalities were found, indicating that they must somehow be part of the same neoplastic process in spite of being anatomically distinct.

Hemiepiphyseal stapling for ankle valgus in multiple hereditary exostoses

If left uncorrected, valgus ankle deformity in multiple hereditary exostoses can cause significant disability in skeletally immature children and in adults. Various management methods have been described, including hemiepiphyseal stapling, transphyseal screw placement, fibular-Achilles tenodesis, distal tibial osteotomy, and ablative epiphyseodesis. In this article, we report the cases of 3 skeletally immature children who had undergone hemiepiphyseal stapling of the medial distal tibial epiphysis for correction of valgus ankle deformity in multiple hereditary exostoses. Correction of the tibiotalar axis, in relation to chronological and bone age, was evaluated. Hemiepiphyseal stapling of the medial distal tibial epiphysis provides ipsilateral corrective potential while allowing staple removal for reversal of growth retardation. This procedure is useful in the management of ankle valgus in multiple hereditary exostoses.

HSPG-deficient zebrafish uncovers dental aspect of multiple osteochondromas

Multiple Osteochondromas (MO; previously known as multiple hereditary exostosis) is an autosomal dominant genetic condition that is characterized by the formation of cartilaginous bone tumours (osteochondromas) at multiple sites in the skeleton, secondary bursa formation and impingement of nerves, tendons and vessels, bone curving, and short stature. MO is also known to be associated with arthritis, general pain, scarring and occasional malignant transformation of osteochondroma into secondary peripheral chondrosarcoma. MO patients present additional complains but the relevance of those in relation to the syndromal background needs validation. Mutations in two enzymes that are required during heparan sulphate synthesis (EXT1 or EXT2) are known to cause MO. Previously, we have used zebrafish which harbour mutations in ext2 as a model for MO and shown that ext2^−/− fish have skeletal defects that resemble those seen in osteochondromas. Here we analyse dental defects present in ext2^−/− fish. Histological analysis reveals that ext2^−/− fish have very severe defects associated with the formation and the morphology of teeth. At 5 days post fertilization 100% of ext2^−/− fish have a single tooth at the end of the 5^th pharyngeal arch, whereas wild-type fish develop three teeth, located in the middle of the pharyngeal arch. ext2^−/− teeth have abnormal morphology (they were shorter and thicker than in the WT) and patchy ossification at the tooth base. Deformities such as split crowns and enamel lesions were found in 20% of ext2^+/− adults. The tooth morphology in ext2^−/− was partially rescued by FGF8 administered locally (bead implants). Our findings from zebrafish model were validated in a dental survey that was conducted with assistance of the MHE Research Foundation. The presence of the malformed and/or displaced teeth with abnormal enamel was declared by half of the respondents indicating that MO might indeed be also associated with dental problems.

[Genetic basis for skeletal disease. Genetic defects in chondrodysplasia]

Chondrodysplasia is a subset of skeletal dysplasia caused by genetic defects affecting chondrogenesis and its development, showing abnormal shape and structure of the skeleton. Pathology of growth plate results in defective skeletal development, such as short stature, while pathology of articular cartilage predisposes degenerative skeletal disease, such as early-onset osteoarthritis. Recently identified genetic basis for chondrodysplasia contributed much in understanding the biology and pathology of cartilage. The accumulated knowledge would be a clue to develop fundamental treatment for chondrodysplasia.

A mouse model of chondrocyte-specific somatic mutation reveals a role for Ext1 loss of heterozygosity in multiple hereditary exostoses

Multiple hereditary exostoses (MHE) is one of the most common skeletal dysplasias, exhibiting the formation of multiple cartilage-capped bony protrusions (osteochondroma) and characteristic bone deformities. Individuals with MHE carry heterozygous loss-of-function mutations in Ext1 or Ext2, genes which together encode an enzyme essential for heparan sulfate synthesis. Despite the identification of causative genes, the pathogenesis of MHE remains unclear, especially with regard to whether osteochondroma results from loss of heterozygosity of the Ext genes. Hampering elucidation of the pathogenic mechanism of MHE, both Ext1(+/-) and Ext2(+/-) heterozygous mutant mice, which mimic the genetic status of human MHE, are highly resistant to osteochondroma formation, especially in long bones. To address these issues, we created a mouse model in which Ext1 is stochastically inactivated in a chondrocyte-specific manner. We show that these mice develop multiple osteochondromas and characteristic bone deformities in a pattern and a frequency that are almost identical to those of human MHE, suggesting a role for Ext1 LOH in MHE. Surprisingly, however, genotyping and fate mapping analyses reveal that chondrocytes constituting osteochondromas are mixtures of mutant and wild-type cells. Moreover, osteochondromas do not possess many typical neoplastic properties. Together, our results suggest that inactivation of Ext1 in a small fraction of chondrocytes is sufficient for the development of osteochondromas and other skeletal defects associated with MHE. Because the observed osteochondromas in our mouse model do not arise from clonal growth of chondrocytes, they cannot be considered true neoplasms.

Hereditary multiple exostoses: case report

OBJECTIVE

Hereditary Multiple Exostoses (HME) is a genetically transmitted bone dysplasia that is inherited in an autosomal dominant manner. It usually presents after the age of two years as multiple bony growths on the appendicular skeleton. As a rare condition (incidence of 0.9-2/100,000), it is not commonly seen in our environment. This paper presents the clinical and radiological features of two patients seen in our hospital within a period of six months.

METHOD

The case records of two patients with hereditary multiple exostoses are presented to highlight the clinical presentation and management options of the condition.

RESULTS

A boy and a girl who respectively manifested the features of hereditary multiple exostoses at the age of two and six years are presented. The main presenting features were painless progressively increasing bony swellings in both upper and lower limbs, with forearm deformity and ulnar deviation of the wrist. One of them had pressure symptoms which necessitated surgical excision of the symptomatic exostosis. Fine needle aspiration cytology confirmed the diagnosis ofosteochondroma.

CONCLUSION

Hereditary multiple exostoses though rare, do occur in our environment and the management is essentially by masterly inactivity except when the bony swellings exhibit any complications or there is concomitant deformity.

[Clinicopathologic study of Ollier's disease and its chondrosarcomatous transformation]

OBJECTIVE

To explore the clinicopathologic features of Ollier's disease, its chondrosarcomatous transformation and related differential diagnoses.

METHODS

A total of 19 cases of Ollier's disease and 8 control cases of pure multiple enchondroma were investigated by imaging studies including X-ray, CT or MRI, and hematoxylin and eosin stain.

RESULTS

Among 19 cases of Ollier's disease, 12 were men and 7 were women with a mean age of 20 years (range, 5-66 years). Ollier's disease involving short tubular bones of extremity were lytic defects with bony expansion, thinning or disappearance of the overlying cortex surrounded by periosteal fibrous tissues. When occurring in the long bones, the disease showed radiolucent columns of dysplastic cartilage that extended from the metaphysis to diaphyseal and created bowing deformation and limb asymmetry. Microscopically, the cartilage present in the small bones of the hands and feet tended to be more hypercellular with more abundant enlarged or binucleated nuclei. The lesion in long bones appeared multicentric, surrounding with a thin rim of bone and calcification. Six cases of Ollier's disease had developed secondary low-grade chondrosarcoma.

CONCLUSIONS

Low-grade chondrosarcomatous transformation can occur in dysplastic cartilage of Ollier's disease. The diagnosis of such sarcomatous transformation should be determined by invasion, but not atypicality of the cartilagenous cells. There are certain differences between the secondary chondrosarcoma of Ollier's disease and conventional chondrosarcoma on clinical, radiographical and pathological grounds.

[Clinicopathologic features of osteochondroma with malignant transformation]

OBJECTIVE

To investigate the clinicopathologic, radiological and immunohistochemical characteristics of osteochondroma with malignant transformation.

METHODS

The clinical data, radiological imagings and hematoxylineosin stained histologic sections were reviewed in 463 cases of osteochondroma diagnosed in Shanghai 6th Hospital from 1991 to 2008, including 11 cases with malignant transformation. Immunohistochemical two-step staining was used to detect CK, vimentin, S-100 protein, p53 and c-myc expression in seven cases of osteochondroma with malignant transformation and 10 cases without malignant transformation. The relevant literature was reviewed.

RESULTS

Among the 11 cases with malignant transformation, five were single osteochondroma (5/408, 1.2%), and six were multiple osteochondromas (6/55, 10.9%). The male to female ratio was 10:1. These 11 cases were derived from femur (4 cases), tibia (3 cases), ilium (3 cases), shoulder bone (1 case) and pubis (1 case). There was one case that showed malignant transformation in both the femur and ilium. The mean ages for the malignant and non-malignant cases were 39.8 years and 20.4 years respectively. All the malignant cases showed large sized lesions with prominent calcification in the thick cartilage caps. The malignant component was low grade, peripheral chondrosarcoma (grade I-II). In some areas the tumor cells infiltrated the peripheral soft tissue and bone marrow. Of the seven cases with malignant transformation that had immunohistochemical staining, all were positive for vimentin and S-100 protein; p53 protein was positive in 2 of 7 cases.

CONCLUSIONS

Malignant transformation of osteochondroma was usually encountered in multiple lesions. Most patients were more than 30 years old with a long clinical history and with a male predominance. These tumors showed thick cartilage caps with prominent calcification. The lobulated nature of the tumors was evident and they infiltrated the surrounding soft tissue. The sarcomatoid component was peripheral type, well differentiated chondrosarcoma. p53 mutation may explain part of the molecular mechanism in the malignant transformation.

[A giant thoracoabdominal tumor--hereditary multiple exostoses]

Hereditary multiple exostoses (HME), also known as osteochondromatosis, is an inherited, autosomal dominant disorder in which multiple osteochondromas develop throughout the skeleton. We present the case of a 17 years old boy diagnosticated with HME with multiple prior orthopedic interventions for upper and lower limbs deformant osteochondromas. He was admitted in our service for a giant osteochondroma localized at the left thoraco-abdominal border arising from C11, C12 ribs, involving the thoracic postero-bazal wall, the abdominal posterior wall and practically the entire left retroperitoneal space. We performed the total resection of this giant tumor (2.6 kg) with postero-inferior thoracic parietectomy (10 to 12 ribs) and abdominal postero-lateral parietectomy followed by the thoraco-abdominal parietal reconstruction with a dual-mesh soft tissue patch, after the high reinsertion of the left diaphragm. The postoperative results were very good from both points of view: esthetical and functional, with preservation of the diaphragm activity and the anatomical reposition of the abdominal viscera. The paper refers to the etiopathogenesis, clinical symptoms, diagnostic, and therapeutic considerations of HME.

Multiple osteochondromas

Multiple osteochondromas (MO) is characterised by development of two or more cartilage capped bony outgrowths (osteochondromas) of the long bones. The prevalence is estimated at 1:50,000, and it seems to be higher in males (male-to-female ratio 1.5:1). Osteochondromas develop and increase in size in the first decade of life, ceasing to grow when the growth plates close at puberty. They are pedunculated or sessile (broad base) and can vary widely in size. The number of osteochondromas may vary significantly within and between families, the mean number of locations is 15-18. The majority are asymptomatic and located in bones that develop from cartilage, especially the long bones of the extremities, predominantly around the knee. The facial bones are not affected. Osteochondromas may cause pain, functional problems and deformities, especially of the forearm, that may be reason for surgical removal. The most important complication is malignant transformation of osteochondroma towards secondary peripheral chondrosarcoma, which is estimated to occur in 0.5-5%. MO is an autosomal dominant disorder and is genetically heterogeneous. In almost 90% of MO patients germline mutations in the tumour suppressor genes EXT1 or EXT2 are found. The EXT genes encode glycosyltransferases, catalyzing heparan sulphate polymerization. The diagnosis is based on radiological and clinical documentation, supplemented with, if available, histological evaluation of osteochondromas. If the exact mutation is known antenatal diagnosis is technically possible. MO should be distinguished from metachondromatosis, dysplasia epiphysealis hemimelica and Ollier disease. Osteochondromas are benign lesions and do not affect life expectancy. Management includes removal of osteochondromas when they give complaints. Removed osteochondromas should be examined for malignant transformation towards secondary peripheral chondrosarcoma. Patients should be well instructed and regular follow-up for early detection of malignancy seems justified. For secondary peripheral chondrosarcoma, en-bloc resection of the lesion and its pseudocapsule with tumour-free margins, preferably in a bone tumour referral centre, should be performed.

[Osteocartilaginous exostoses (osteochondromas)]

Osteochondroma is the most common true bone neoplasm formed by a cartilage capped bony projection arising on the external surface of a bone containing a marrow cavity that is continuous with that of the underlying bone. Osteochondromas generally arise in the bones preformed by cartilage. Osteochondromas may be solitary and multiple. Most reported cases have been in the first 3 decades with no known sex predilection. The lesion has three layers - perichondrium, cartilage and bone. The cartilage cap is usually less than 2.0 cm thick, superficial chondrocytes are clustered, the ones close to the transition to the bone resemble a growth plate, they are organized into chords and undergo enchondrial ossification. Loss of the architecture of cartilage, wide fibrous bands, myxoid change, increased chondrocyte cellularity, mitotic activity, significant chondrocyte atypia and necrosis are all features that may indicate secondary malignant transformation.

Clinical outcome and genotype in patients with hereditary multiple exostoses

Hereditary multiple exostoses (HME) is an autosomal dominant skeletal disorder with a wide spectrum of clinical manifestations. In 52 out of 60 individuals from HME+ families, exostoses became clinically apparent. In this study, the clinical and radiological outcome of these 52 HME patients (19 families) was investigated by medical history, clinical examination, and radiographs. In addition to correlating phenotype with genotype, a linkage/exclusion analysis was performed in 35 HME patients. We found several correlations between HME genes (EXT1, EXT2) and phenotype. Compared to EXT2-linkage, female individuals with EXT1-linkage were smaller in stature. Patients with EXT1-linkage and patients with undetermined linkage (EXT?) were more severely affected, underwent more surgeries, and showed a higher number of exostoses at follow-up. Moreover, we found an increased phenotype risk for limb shortening for EXT1- and EXT?-linkage. This study corresponds to data of other investigators who showed that EXT1 mutations are associated with a more severe phenotype than other EXT forms. (c) 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1541-1551, 2007.

Evaluation of the anatomic burden of patients with hereditary multiple exostoses

Hereditary multiple exostosis (HME) is an autosomal dominant condition resulting predominantly from mutations in the exostosin 1 (EXT1) and exostosin 2 (EXT2) genes. We asked two questions in our study: first, what is the anatomic burden of subjects with HME; second, is there a difference in anatomic burden in subjects with EXT 1 versus EXT 2. The anatomic burden experienced by HME patients was defined according to three domains: (1) lesion quality; (2) limb malalignment and deformity; and (3) limb segment lengths and percentile height. Seventy-nine subjects with HME were included in this study. Of these 79 phenotypes were completed. Forty-eight genotypes were confirmed leaving 48 complete genotype-phenotype profiles for analysis. Analysis of the coding and flanking intronic regions of EXT1 and EXT2 was performed in each patient by direct sequencing of PCR-amplified genomic DNA. All three domains of anatomic burden showed a wide range of presentation in the HME study sample. More lesions and greater tendency to flat bone occurrence was associated with EXT1. EXT1 patients were shorter. All limb segments tended to be shorter for EXT1 subjects. EXT1 subjects showed more anatomic burden with respect to lesion quality and height.

Multiple exostosis: a short study of abnormalities near the growth plate

The pathogenesis of multiple exostosis has been controversial with many theories put forward including the structural/mechanical theory, which emphasizes that the osteochondroma arises in the displaced growth plate cartilage penetrating a defective periosteum. Recently, molecular genetics has offered the neoplastic model with tumor suppressor genes implicated in the development and pathogenesis of exostosis. In this study, we demonstrated the spectrum of histological abnormalities in the developing exostosis present on the surface of the bone at the physis. Seven skeletally immature patients with multiple exostoses were used in this study. The patients' families were advised of and consented to the proposed study. Coincident with removal of symptomatic exostoses that was adjacent to the physis, a thin strip of bone with overlying periosteum was removed to include the edge of the physis. This was followed by formalin fixation and routine paraffin embedding. We demonstrated the earliest lesion as a microchondroma within the periosteum adjacent to the normal physis (also called the 'groove of Ranvier'). More mature progressively larger lesions showing enchondral ossification were seen distally. The periosteum and the perichondrium were intact with normal physis. Our observations give support to the fact that precursor cells in the periosteum adjacent to the physis (also called the 'groove of Ranvier') gives rise to the chondrocytes that clonally expands and develops into exostosis.

Short-Limbed Dwarfism: slw Is a New Allele of Npr2 Causing Chondrodysplasia

Short-limbed dwarfism (SLW) is a new mutant mouse characterized by a dwarf phenotype with markedly short body, limbs, and tail. In the present study, we investigated the skeletal phenotypes of the SLW mouse and determined the chromosomal localization to identify the gene responsible for the phenotypes (slw). Skeletal preparations stained with alcian blue and alizarin red revealed that longitudinal growth of the extremities of the affected (slw/slw) mice was significantly reduced in comparison with that of normal mice, whereas the positions and numbers of skeletal elements were normal. Histological examination of tibial growth plates of the affected mice showed that the numbers of proliferating and hypertrophic chondrocytes were obviously diminished. These phenotypes resembled to those of human chondrodysplasias caused by defective chondrocyte proliferation and differentiation. We mapped the slw locus on an 11.7-cM interval of the proximal region of mouse chromosome 4 by linkage analysis. Furthermore, allelism test using Npr2(cn) locus, a mutant allele of Npr2 gene encoding a natriuretic peptide receptor B, revealed that slw locus is an allele of the Npr2 gene. These results suggest that the dwarf phenotype of the SLW mouse is caused by the disturbed endochondral ossification, and a mutation in the Npr2 gene is expected to be responsible for the phenotypes of the SLW mouse.

Sarcomatous transformation in diaphyseal aclasis

Multiple hereditary exostosis (or diaphyseal aclasis) is a condition characterized by the development of multiple osteochondromas. The tendency for malignant transformation into chondrosarcoma is well known. Malignancy typically arises from the cartilaginous cap of the osteochondroma. Radiographs supplemented by computed tomography have an important role in the diagnosis of this condition. Magnetic resonance imaging shows the features of sarcomatous change and aids in differentiating malignancy from pseudotumours.

Dysplasia epiphysealis hemimelica (Trevor disease): a rare developmental disorder of bone mimicking osteochondroma of long bones

Dysplasia epiphysealis hemimelica (DEH) is a rare developmental disorder of childhood and is characterized by asymmetric enlargement of the epiphyseal cartilage of the long bones. After 4 to 5 years of age, the lesions histologically resemble osteochondroma. To our knowledge, only one publication of this entity is available in an English pathology journal. The clinical, radiographic, and histologic features of 9 cases of DEH were retrospectively reviewed. The patients' age ranged from 3 to 15 years with single or multiple lesions of the femur, fibula, tibia, and talus. The etiology and pathogenesis of DEH are not known. Its origin and evolution has initially apparent similarities to the development and growth of epiphyseal secondary ossification centers. DEH can be differentiated from osteochondroma of long bones using clinical, radiologic, and pathologic parameters. DEH occurs in young children and adolescents manifesting as lesions that arise particularly from the epiphysis of the lower extremities and tarsus. Osteochondroma, in contrast, occurs most frequently between 10 and 30 years of age and originates from the metaphysis of long bones. Although the DEH cartilage resembles osteochondroma, there are several significant histologic differences. During infancy, lesions of DEH histologically reveal osteocartilaginous nodules that resemble secondary ossification centers. Usually after 4 to 5 years of age they develop into osteochondroma-like lesions. Although all cases of DEH contain small areas of calcified cartilage beneath the cartilage cap, a significant percentage of osteochondromas show large amounts. The nodules and cartilage cap of DEH contain bands of cartilage separating areas of cancellous bone; these bands are not present in osteochondroma. Among the other distinguishable features, recent molecular studies of DEH demonstrated normal expression levels of EXT1 and EXT2 genes, comparable to that of normal growth plate. Osteochondroma, in contrast, has low levels of EXT1 and EXT2 gene expression due to gene mutation. The histologic differences in combination with the distinct clinical and radiographic features should enable a pathologist to differentiate these entities.

Calcaneal osteochondroma

Osteochondromas are essentially the most common primary bone tumors. These benign cartilage producing neoplasms are generally asymptomatic and have a relatively small potential for adverse effects. HME, the familial form of this tumor, is associated with a greater incidence of complications, the most significant of which is sarcomatous degeneration to secondary chondrosarcomas. Various imaging techniques can be used to characterize these lesions, but in the absence of symptoms or signs of complications, plain-film radiography is usually sufficient for diagnosis as this tumor has a characteristic radiographic appearance. Once this benign tumor is identified and more serious forms of tumor are ruled out, treatment is generally not needed. If a malignancy is suspected, however, complete surgical excision is the preferred treatment as this usually ensures long term survival.

Defective chondrocyte proliferation and differentiation in osteochondromas of MHE patients

Multiple hereditary exostoses (MHE) is an autosomal dominant skeletal disorder caused by mutations in one of the two EXT genes and characterized by multiple osteochondromas that generally arise near the ends of growing long bones. Defective endochondral ossification is likely to be involved in the formation of osteochondromas. In order to investigate potential changes in chondrocyte proliferation and/or differentiation during this process, osteochondroma samples from MHE patients were obtained and used for genetic, morphological, immunohistological, and in situ hybridization studies. The expression patterns of IHH (Indian hedgehog) and FGFR3 (Fibroblast Growth Factor Receptor 3) were similar with transcripts expressed throughout osteochondromas. Expression of PTHR1 (Parathyroid Hormone Receptor 1) transcripts was restricted to a narrow zone of prehypertrophic chondrocytes. Numerous cells forming osteochondromas although resembling prehypertrophic chondrocytes, stained positively with an anti-proliferating cell nuclear antigen (PCNA) antibody. In addition, ectopic expression of collagen type I and abnormal presence of osteocalcin (OC), osteopontin (OP), and bone sialoprotein (BSP) were observed in the cartilaginous osteochondromas. These data indicate that most chondrocytes involved in the growth of osteochondromas can proliferate, and that some of them exhibit bone-forming cell characteristics. We conclude that in MHE, defective heparan sulfate biosynthesis caused by EXT mutations maintains the proliferative capacity of chondrocytes and promotes phenotypic modification to bone-forming cells.

Short rib-polydactyly syndrome: lethal chondrodysplasia associated with brain malformations in a 35-week-gestation infant

This case report describes the neuropathological findings in an autopsy case of short rib-polydactyly syndrome (SRPS). The patient was a Japanese female neonate who was born at 35 weeks of gestation and died soon after birth due to severe cardiopulmonary insufficiency. Clinical and radiological findings were most consistent with SRPS type I (Saldino-Noonan type). General autopsy findings included situs inversus, persistent truncus arteriosus and endocardial cushion defect, hypoplastic lungs and adrenal glands, and vaginal atresia. Fixed brain weight was 330 g. Three different categories of pathological changes were detected in the brain. These were as follows: (1) multiple cyst formation in the parenchyma, (2) primary malformations of the nervous and mesenchymal tissues, and (3) deposition of an unusual substance in the cerebral white matter. The multiple cysts or cavities in the parenchyma may be due to severe hypoxic-ischemic insults related to the congenital heart anomaly. The primary malformations were summarized as follows: (1) capillary telangiectasia of the pia mater and choroid plexus, (2) olfactory dysplasia with asymmetry, (3) focal cortical dysplasia in the frontal lobe and cerebellum, (4) olivary dysplasia, and (5) enlargement of the posterior part of the lateral ventricle. Dysplastic changes of the nervous tissue can be classified into the group of neuronal migration disorders. Although biochemical properties of the unknown substance were not determined, it is considered to be some product derived from an inborn error of metabolism. Morphological data of SRPS is still scarce, and pathognomonic changes have not yet been elucidated. The present data suggests that coexistence of the nervous and mesenchymal malformations may be highly characteristic of SRPS.

Novel mutations in the EXT1 gene in two consanguineous families affected with multiple hereditary exostoses (familial osteochondromatosis)

Multiple hereditary exostoses (HME) is an autosomal dominant developmental disorder exhibiting multiple osteocartilaginous bone tumors that generally arise near the ends of growing long bones. Here, we report two large consanguineous families from Pakistan, who display the typical features of HME. Affected individuals also show a previously unreported feature--bilateral overriding of single toes. Analysis using microsatellite markers for each of the known EXT loci, EXT1, EXT2, and EXT3 showed linkage to EXT1. In the first family, mutation analysis of the EXT1 gene revealed that affected individuals were heterozygous for an in-frame G-to-C transversion at the conserved splice donor site in intron 1. This mutation is predicted to disrupt splicing of the first intron and produce a frameshift that leads to a premature termination codon. In the second family, an insertion of an A in exon 8 is predicted to produce a frameshift at codon 555 followed by a premature termination, a further 10 codons downstream. In both families, an increased number of affected male subjects were observed. In affected females in family 2, phenotypic variability and incomplete penetrance were noted.

Severity of disease and risk of malignant change in hereditary multiple exostoses. A genotype-phenotype study

We performed a prospective genotype-phenotype study using molecular screening and clinical assessment to compare the severity of disease and the risk of sarcoma in 172 individuals (78 families) with hereditary multiple exostoses. We calculated the severity of disease including stature, number of exostoses, number of surgical procedures that were necessary, deformity and functional parameters and used molecular techniques to identify the genetic mutations in affected individuals. Each arm of the genotype-phenotype study was blind to the outcome of the other. Mutations EXT1 and EXT2 were almost equally common, and were identified in 83% of individuals. Non-parametric statistical tests were used. There was a wide variation in the severity of disease. Children under ten years of age had fewer exostoses, consistent with the known age-related penetrance of this condition. The severity of the disease did not differ significantly with gender and was very variable within any given family. The sites of mutation affected the severity of disease with patients with EXT1 mutations having a significantly worse condition than those with EXT2 mutations in three of five parameters of severity (stature, deformity and functional parameters). A single sarcoma developed in an EXT2 mutation carrier, compared with seven in EXT1 mutation carriers. There was no evidence that sarcomas arose more commonly in families in whom the disease was more severe. The sarcoma risk in EXT1 carriers is similar to the risk of breast cancer in an older population subjected to breast-screening, suggesting that a role for regular screening in patients with hereditary multiple exostoses is justifiable.

Proximal 11p deletion syndrome (P11pDS): additional evaluation of the clinical and molecular aspects

The combination of multiple exostoses (EXT) and enlarged parietal foramina (foramina parietalia permagna, FPP) represent the main features of the proximal 11p deletion syndrome (P11pDS), a contiguous gene syndrome (MIM 601224) caused by an interstitial deletion on the short arm of chromosome 11. Here we present clinical aspects of two new P11pDS patients and the clinical follow-up of one patient reported in the original paper describing this syndrome. Recognised clinical signs include EXT, FPP, mental retardation, facial asymmetry, asymmetric calcification of coronary sutures, defective vision (severe myopia, nystagmus, strabismus), skeletal anomalies (small hands and feet, tapering fingers), heart defect, and anal stenosis. In addition fluorescence in situ hybridisation and molecular analysis were performed to gain further insight in potential candidate genes involved in P11pDS.

The short-lived exostosis induced surgically versus the lasting genetic hereditary multiple exostoses

Hereditary osteochondromas are often caused by mutation in the EXT1 gene. The lesions are typified by formation of a "pseudo" growth plate like lesion growing at 60 degrees to the normal growth direction of the bone. Such lesions can be mimicked surgically by reverting the position--the polarity of the zone of LaCroix. The current study attempts to compare the pathology between EXT1 gene expression in humans and surgically created osteochondroma pathology in a rat model. Tissues of human bunion, human embryonal tissue, and human adult cartilage as well as normal rat epiphyses served as controls. Rats were operated on and a 60 degree span of the ring of LaCroix was inverted as described by Delgado (Delgado, E., Rodriguez, J. I., Serada, A., Tellez, M., and Pariagoa, R.. Clin. Orthop. 201, 251-258 (1985)). The surgically created osteochondromas were assessed by histology, histochemistry, and immunohistochemistry. The findings show that the surgically created lesions contain only a small amount of FGF receptor 3 (FGFR3) expressed on mesenchymal stem cells located in the perichondrium, as compared to the cell population carrying FGFR3 in the contralateral limb. Indian hedgehog and Bcl2 are downregulated, while BMP-2 is overexpressed in the operated limb, compared to the LaCroix ring of the contralaetral limb. The shortage, as well as the disturbed migration routes of the residual mesenchymal stem cells in surgically created osteochondromas leads eventually to resorption of the pathological elements. In search of additional markers characterizing such pathological structures composed of mesenchymal stem cells and cartilaginous and bony cells, EXT1 gene was found to be expressed in the surgically created osteochondromas, like in normal growth plates. Nitric oxide synthase was also expressed like in adult cartilage, though tumor necrosis factor alpha typifying Bunion formation was absent. In summary, surgically created osteochondromas lack the massive and continuous population of mesenchymal stem cells with Bcl2 expression. However, the small residual mesenchymal cell population gives rise to short-lived EXT1-expressing cells that disappear eventually due to spontaneous resorption.

Multiple exostoses, mental retardation, hypertrichosis, and brain abnormalities in a boy with a de novo 8q24 submicroscopic interstitial deletion

Multiple exostoses represent a genetically heterogeneous disorder that may occur isolated or as part of a complex contiguous gene syndrome such as Langer-Giedion syndrome on chromosome 8 and the proximal 11p deletion syndrome on chromosome 11. Here we describe a boy with multiple exostoses, hypertrichosis, mental retardation, and epilepsy due to a de novo deletion on chromosome 8q24. Molecular analysis revealed that the deletion interval overlaps with the Langer-Giedion syndrome and involves the EXT1 gene and additional genes located distal to EXT1, but probably not encompassing the TRPS1 gene located proximal to EXT1.