Deactivating germline mutations in LEMD3 cause osteopoikilosis and Buschke-Ollendorff syndrome, but not sporadic melorheostosis

Unraveling melorheostosis: insights into clinical features, diagnosis, and treatment

Melorheostosis is a rare bone disease characterized by abundant bone formation with a characteristic radiographic appearance that resembles "dripping candle wax." Recent data have shown that the majority of cases are due to somatic activating mutations in bone. Melorheostosis has several clinical and radiographic presentations, which are now known to be caused by different somatic mutations such as MAP2K1, SMAD3, KRAS, and LEMD3. This review provides a comprehensive look at the clinical features, diagnostic approaches, and current treatment options for melorheostosis, alongside future research directions aimed at improving patient outcomes.

Bone Health ECHO Case Report: High Bone Mass in a Patient with Chronic Kidney Disease

Bone Health ECHO (Extension of Community Healthcare Outcomes) is a growing family of online educational programs. Its mission is to enhance delivery of best practice skeletal healthcare worldwide. Each program typically consists of a didactic lecture and discussion of clinical cases with diagnostic and treatment dilemmas. Here we present a Bone Health ECHO case of a 39-year-old man who has received hemodialysis for 12 years. This case is characterized by the development of chronic kidney disease - mineral and bone disorder (CKD-MBD) which was managed using conservative treatment to maintain phosphate and calcium levels within the reference range in spite of severe secondary hyperparathyroidism, after the patient declined parathyroidectomy. Although this patient had multiple vertebral fractures with height loss, his bone mineral density was higher than expected for his age and gradually increased over the period of observation. Whole-exome sequencing showed a heterozygous, likely pathogenic variant in LEMD3 gene (13 exon HG38, chr12:65246271dup, с.2682dup in a heterozygous state), which may explain the high bone mass phenotype. As a result of the ECHO presentation, we decided that successful treatment of CKD-MBD would be the most effective approach to managing his bone fragility. His high bone mass phenotype was most likely associated with LEMD3 gene variant. This patient does not require any specific anti-osteoporotic treatment at this time; however, he is likely to benefit from parathyroid surgery.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

The LEM-ESCRT toolkit: Repair and maintenance of the nucleus

The eukaryotic genome is enclosed in a nuclear envelope that protects it from potentially damaging cellular activities and physically segregates transcription and translation.Transport across the NE is highly regulated and occurs primarily via the macromolecular nuclear pore complexes.Loss of nuclear compartmentalization due to defects in NPC function and NE integrity are tied to neurological and ageing disorders like Alzheimer’s, viral pathogenesis, immune disorders, and cancer progression.Recent work implicates inner-nuclear membrane proteins of the conserved LEM domain family and the ESCRT machinery in NE reformation during cell division and NE repair upon rupture in migrating cancer cells, and generating seals over defective NPCs. In this review, we discuss the recent in-roads made into defining the molecular mechanisms and biochemical networks engaged by LEM and many other integral inner nuclear membrane proteins to preserve the nuclear barrier.

Clinical characteristics of 10 Chinese patients with melorheostosis and identification of a somatic MAP2K1 variant in one case

Background

Melorheostosis (MEL) is an exceptionally rare sclerosing bone dysplasia with asymmetrically exuberant bone formation and soft tissue lesions in a segmental distribution. We aimed to summarize the clinical characteristics of Chinese MEL patients and identify their pathogenic cause.

Methods

In total, 10 Chinese MEL patients were recruited, and clinical manifestations and radiological characteristics were recorded. Sanger sequencing of the LEMD3 gene was performed on peripheral blood samples of all patients, while the exome sequencing of matched peripheral blood, melorheostotic bone, and skin lesion samples was conducted on one patient who provided affected bone and skin tissues. Micro‐computed tomography (micro‐CT) was also used to scan the melorheostotic bone tissue.

Results

We found the average age of the 10 MEL patients was 29.5 years (range 11–40 years), and the major symptoms were bone pain, restricted movement, and bone deformity. The lesions sites were mainly located in femur (8/10), tibia (8/10), fibula (6/10), and foot (7/10), the next was pelvis (4/10), and the last were patella (1/10), hand (1/10) and spine (1/10). Radiological examinations showed a mixture of hyperostosis consisting of classic “dripping candle wax,” “osteoma‐like,” or “myositis ossificans‐like” patterns in most patients. No germline pathogenic variants in the LEMD3 gene were found in all patients, but a disease‐causing somatic variant of MAP2K1 (c.167A > C, p.Gln56Pro) was detected in melorheostotic bone from one patient. Moreover, the micro‐CT analysis showed increased porosity in the melorheostotic bone with somatic MAP2K1 variant.

Conclusion

This is a summary of the clinical characteristics of Chinese MEL patients and we first identify the somatic MAP2K1 variant in Chinese patients. Our findings validate the molecular genetic mechanism of MEL and broaden its phenotype spectrum in the Chinese population.

Case Report: Two New Cases of Chromosome 12q14 Deletions and Review of the Literature

Interstitial deletions on the long arm of chromosome 12 (12q deletions) are rare, and are associated with intellectual disability, developmental delay, failure to thrive and congenital anomalies. The precise genotype-phenotype correlations of different deletions has not been completely resolved. Ascertaining individuals with overlapping deletions and complex phenotypes may help to identify causative genes and improve understanding of 12q deletion syndromes. We here describe two individuals with non-overlapping 12q14 deletions encountered at our clinical genetics outpatient clinic and perform a review of all previously published interstitial 12q deletions to further delineate genotype-phenotype correlations. Both individuals presented with a neurodevelopmental disorder with various degrees of intellectual disability, failure to thrive and dysmorphic features. Previously, larger deletions overlapping large parts of the deletions encountered in both individuals have been described. Whereas, individual 1 seems to fit into the previously described phenotypic spectrum of the 12q14 microdeletion syndrome, individual 2 displays more severe neurological symptoms, which are likely caused by haploinsufficiency of the BAF complex member SMARCC2, which is included in the deletion. We furthermore perform a review of all previously published interstitial 12q deletions which we found to cluster amongst 5 regions on chromosome 12, to further delineate genotype-phenotype correlations, and we discuss likely disease relevant genes for each of these deletion clusters. Together, this expands knowledge on deletions on chromosome 12q which might facilitate patient counseling. Also, it illustrates that re-analysis of previously described microdeletions syndromes in the next generation sequencing era can be useful to delineate genotype-phenotype correlations and identify disease relevant genes in individuals with neurodevelopmental disorders.

The Diverse Cellular Functions of Inner Nuclear Membrane Proteins

The nuclear compartment is delimited by a specialized expanded sheet of the endoplasmic reticulum (ER) known as the nuclear envelope (NE). Compared to the outer nuclear membrane and the contiguous peripheral ER, the inner nuclear membrane (INM) houses a unique set of transmembrane proteins that serve a staggering range of functions. Many of these functions reflect the exceptional position of INM proteins at the membrane-chromatin interface. Recent research revealed that numerous INM proteins perform crucial roles in chromatin organization, regulation of gene expression, genome stability, and mediation of signaling pathways into the nucleus. Other INM proteins establish mechanical links between chromatin and the cytoskeleton, help NE remodeling, or contribute to the surveillance of NE integrity and homeostasis. As INM proteins continue to gain prominence, we review these advancements and give an overview on the functional versatility of the INM proteome.

Bisphosphonate Therapy in the Management of Symptomatic Melorheostosis of Tibia

INTRODUCTION

Melorheostosis is a rare sclerosing bone disease characterized by linear hyperostotic bone dysplasia with its radiological appearance as melting candle wax dripping by its side. It usually affects long bones, especially the lower limb. The exact cause of the disease has not been clearly explained though many theories are available. It is insidious in onset and symptoms being pain, deformity, and joint stiffness. Although there is no definitive treatment, the administration of bisphosphonates dramatically reduces pain and improves the patient clinically.

CASE REPORT

We described a case of a 28-year-old female who presented with a history of pain and swelling in her left leg for the past 2 years. The onset of complaints was insidious. On physical examination, there was tender swelling over the shaft of the tibia with irregular borders. Knee and ankle range of movements were normal. Radiographs showed hyperostosis of the proximal two-thirds of the tibia of the left leg with a flowing candle wax appearance. The patient was treated with a single dose of intravenous zolendronic acid and physical therapy. The patient had dramatic alleviation of pain without the need for any further treatment till 1 year follow-up.

CONCLUSION

Although there is no specific treatment available for this disease, the intravenous infusion of zolendronic acid has dramatically improved the patient clinically.

Somatic SMAD3-activating mutations cause melorheostosis by up-regulating the TGF-β/SMAD pathway

Melorheostosis is a rare sclerosing dysostosis characterized by asymmetric exuberant bone formation. Recently, we reported that somatic mosaicism for MAP2K1-activating mutations causes radiographical “dripping candle wax” melorheostosis. We now report somatic SMAD3 mutations in bone lesions of four unrelated patients with endosteal pattern melorheostosis. In vitro, the SMAD3 mutations stimulated the TGF-β pathway in osteoblasts, enhanced nuclear translocation and target gene expression, and inhibited proliferation. Osteoblast differentiation and mineralization were stimulated by the SMAD3 mutation, consistent with higher mineralization in affected than in unaffected bone, but differing from MAP2K1 mutation–positive melorheostosis. Conversely, osteoblast differentiation and mineralization were inhibited when osteogenesis of affected osteoblasts was driven in the presence of BMP2. Transcriptome profiling displayed that TGF-β pathway activation and ossification-related processes were significantly influenced by the SMAD3 mutation. Co-expression clustering illuminated melorheostosis pathophysiology, including alterations in ECM organization, cell growth, and interferon signaling. These data reveal antagonism of TGF-β/SMAD3 activation by BMP signaling in SMAD3 mutation–positive endosteal melorheostosis, which may guide future therapies.

The dripping candle wax sign of melorheostosis

Melorheostosis is a rare benign bone disease including dysostosis and sclerosis. Dripping candle wax presence is a common and typical sign of melorheostosis. This sign appears as irregular hyperostosis of the cortical bone which is likened to melted wax flowing down one side of a candle. It can sometimes cause pain, stiffness joint, or limitation of motion in the affected areas implicitly but mostly has no symptoms. It is usually observed on plain radiography; its appearance is generally hyperplasia on one side of the bone. We report a 33-year-old male who has an incidental diagnosis of melorheostosis post-trauma.

A multi-omics approach expands the mutational spectrum of MAP2K1-related melorheostosis

Melorheostosis is a very rare sclerosing bone dysplasia characterized by asymmetrical and progressive cortical hyperostosis, usually with involvement of soft tissues surrounding the lesions. Recently Kang et al. identified somatic mosaicism for variants (p.Gln56Pro, p.Lys57Asn, or p.Lys57Glu) in the negative regulatory domain of MAP2K1, resulting in increased ERK1/2 signalling in affected tissues. In our study, we employed several sequencing technologies to unravel genetic variants (only present in affected tissues) from four sporadic melorheostosis patients. In the exome of two patients, we identified the same variants (p.K57N and p.K57E) as previously described by Kang et al. WGS and RNAseq analysis in a third patient demonstrated the presence of a novel variant (p.Cys121Ser) in the catalytic domain of MAP2K1. In addition, gene set enrichment analysis of the transcriptome data demonstrated upregulation of proliferative pathways. Interestingly, increased proliferation of MAP2K1 p.Lys57Asn-positive osteoblasts has been reported by Kang et al. The variants located in the hotspot region of the negative regulatory domain as well as this newly identified p.Cys121Ser variant have all been classified as MAP2K1 variants that can constitutively activate the downstream effector Erk. Finally, in a fourth patient with classical radiographic features of melorheostosis, no pathogenic variants could be identified in MAP2K1 or the other candidate genes for melorheostosis (SMAD3; LEMD3; KRAS). In conclusion, our study strongly suggests that not only somatic variants in the regulatory domain of MAP2K1 but also in the catalytic domain can cause melorheostosis. Our observations confirm that mutations in MAP2K1 are a major cause of melorheostosis and also suggest further locus heterogeneity for this disorder.

Modeling-based bone formation transforms trabeculae to cortical bone in the sclerotic areas in Buschke-Ollendorff syndrome. A case study of two females with LEMD3 variants

Buschke-Ollendorff syndrome is a rare autosomal dominant condition caused by pathogenic variants in LEMD3 and characterized by connective tissue nevi and sclerotic bone abnormalities known as osteopoikilosis. The bone phenotype in Buschke-Ollendorff syndrome including osteopoikilosis remains unclear. We investigated bone turnover markers, pelvis and crura X-rays; lumbar spine and femoral neck DXA; bone activity by NaF-PET/CT, bone structure by μCT and dynamic histomorphometry in adults with Buschke-Ollendorff syndrome. Two women aged 25 and 47 years with a BMI of 30 and 32 kg/m², respectively, were included in the investigation. Bone turnover markers were within normal range. aBMD Z-scores were comparable to that of controls in the lumbar spine and increased at the hip. Radiographies exposed spotted areas in crura and pelvis, and NaF-PET/CT exposed abnormal pattern of irregular shaped NaF uptake in the entire skeleton. In both biopsies, μCT showed trabecular structure comparable to that of controls with stellate shaped sclerotic noduli within the cavity and on the endocortex. Histomorphometric analyses of the sclerotic lesions revealed compact lamellar bone with a normal bone remodeling rate, but partly replaced by modeling-based bone formation. Woven bone was not observed in the nodules. Therefore, while bone turnover and BMD were largely within normal reference range in patients with the Buschke-Ollendorff syndrome, osteosclerotic lesions appear to emerge due to modeling-based bone formation with secondary bone remodeling. These observations indicate that LEMD3 may be important for the activation of bone lining cells leading to modeling-based bone formation.

Clinical Evaluation of Melorheostosis in the Context of a Natural History Clinical Study

Melorheostosis is a rare dysostosis involving cortical bone overgrowth that affects the appendicular skeleton. Patients present with pain, deformities, contractures, range of motion limitation(s), and limb swelling. It has been described in children as well as adults. We recently identified somatic mosaicism for gain-of-function mutations in MAP2K1 in patients with melorheostosis. Despite these advances in genetic understanding, there are no effective therapies or clinical guidelines to help clinicians and patients in disease management. In a study to better characterize the clinical and genetic aspects of the disease, we recruited 30 adults with a radiographic appearance of melorheostosis and corresponding increased uptake on ¹⁸F-NaF positron emission tomography (PET)/CT. Patients underwent physical exam, imaging studies, and laboratory assessment. All patients underwent nerve conduction studies and ultrasound imaging of the nerve in the anatomic distribution of melorheostosis. We found sensory deficits in approximately 77% of patients, with evidence of focal nerve entrapment in five patients. All patients reported pain; 53% of patients had changes in skin overlying the affected bone. No significant laboratory abnormalities were noted. Our findings suggest that patients with melorheostosis may benefit from a multidisciplinary team of dermatologists, neurologists, orthopedic surgeons, pain and palliative care specialists, and physical medicine and rehabilitation specialists. Future studies focused on disease management are needed. © 2019 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Distinct Clinical and Pathological Features of Melorheostosis Associated With Somatic MAP2K1 Mutations

Melorheostosis is a rare hyperostotic disease of the long bones classically characterized by a "dripping candle-wax" radiographic appearance. We recently described somatic activating mutations in MAP2K1 as a cause of melorheostosis. Here, we report distinguishing characteristics of patients with MAP2K1-positive melorheostosis. Fifteen unrelated patients with radiographic appearance of melorheostosis underwent paired biopsies of affected and unaffected bone for whole-exome sequencing, histology, and cell culture. Eight patients with mutations in MAP2K1 in affected bone were compared to the seven MAP2K1-negative patients to identify distinguishing characteristics. Patients with MAP2K1-positive melorheostosis had a distinct phenotype with classic "dripping candle-wax" appearance on radiographs (p = 0.01), characteristic vascular lesions on skin overlying affected bone (p = 0.01), and higher prevalence of extraosseous mineralization and joint involvement (p = 0.04 for both). Melorheostotic bone from both MAP2K1-positive and MAP2K1-negative patients showed two zones of distinct morphology-an outer segment of parallel layers of primary lamellar bone and a deeper zone of intensely remodeled highly porous osteonal-like bone. Affected bone from MAP2K1-positive patients showed excessive osteoid (p = 0.0012), increased number of osteoblasts (p = 0.012) and osteoclasts (p = 0.04), and increased vascularity on histology in comparison to paired unaffected bone which was not seen in affected bone in most MAP2K1-negative patients. The identification of a distinct phenotype of patients with MAP2K1-positive melorheostosis demonstrates clinical and genetic heterogeneity among patients with the disease. Further studies are needed to better understand the underlying pathophysiology and associated skin findings. © 2018 American Society for Bone and Mineral Research.

Sclerosing bone dysplasias

The group of sclerosing bone dysplasia's is a clinically and genetically heterogeneous group of rare bone disorders which, according to the latest Nosology and classification of genetic skeletal disorders (2015), can be subdivided in three subgroups; the neonatal osteosclerotic dysplasias, the osteopetroses and related disorders and the other sclerosing bone disorders. Here, we give an overview of the most important radiographic and clinical symptoms, the underlying genetic defect and potential treatment options of the different sclerosing dysplasias included in these subgroups.

Human Genetics of Sclerosing Bone Disorders

PURPOSE OF REVIEW

The group of sclerosing bone disorders encompasses a variety of disorders all marked by increased bone mass. In this review, we give an overview of the genetic causes of this heterogeneous group of disorders and briefly touch upon the value of these findings for the development of novel therapeutic agents.

RECENT FINDINGS

Advances in the next-generation sequencing technologies are accelerating the molecular dissection of the pathogenic mechanisms underlying skeletal dysplasias. Throughout the years, the genetic cause of these disorders has been extensively studied which resulted in the identification of a variety of disease-causing genes and pathways that are involved in bone formation by osteoblasts, bone resorption by osteoclasts, or both processes. Due to this rapidly increasing knowledge, the insights into the regulatory mechanisms of bone metabolism are continuously improving resulting in the identification of novel therapeutic targets for disorders with reduced bone mass and increased bone fragility.

Somatic activating mutations in MAP2K1 cause melorheostosis

Melorheostosis is a sporadic disease of uncertain etiology characterized by asymmetric bone overgrowth and functional impairment. Using whole exome sequencing, we identify somatic mosaic MAP2K1 mutations in affected, but not unaffected, bone of eight unrelated patients with melorheostosis. The activating mutations (Q56P, K57E and K57N) cluster tightly in the MEK1 negative regulatory domain. Affected bone displays a mosaic pattern of increased p-ERK1/2 in osteoblast immunohistochemistry. Osteoblasts cultured from affected bone comprise two populations with distinct p-ERK1/2 levels by flow cytometry, enhanced ERK1/2 activation, and increased cell proliferation. However, these MAP2K1 mutations inhibit BMP2-mediated osteoblast mineralization and differentiation in vitro, underlying the markedly increased osteoid detected in affected bone histology. Mosaicism is also detected in the skin overlying bone lesions in four of five patients tested. Our data show that the MAP2K1 oncogene is important in human bone formation and implicate MEK1 inhibition as a potential treatment avenue for melorheostosis.

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

Melorheostosis: Exome sequencing of an associated dermatosis implicates postzygotic mosaicism of mutated KRAS

Melorheostosis (MEL) is the rare sporadic dysostosis characterized by monostotic or polyostotic osteosclerosis and hyperostosis often distributed in a sclerotomal pattern. The prevailing hypothesis for MEL invokes postzygotic mosaicism. Sometimes scleroderma-like skin changes, considered a representation of the pathogenetic process of MEL, overlie the bony changes, and sometimes MEL becomes malignant. Osteopoikilosis (OPK) is the autosomal dominant skeletal dysplasia that features symmetrically distributed punctate osteosclerosis due to heterozygous loss-of-function mutation within LEMD3. Rarely, radiographic findings of MEL occur in OPK. However, germline mutation of LEMD3 does not explain sporadic MEL. To explore if mosaicism underlies MEL, we studied a boy with polyostotic MEL and characteristic overlying scleroderma-like skin, a few bony lesions consistent with OPK, and a large epidermal nevus known to usually harbor a HRAS, FGFR3, or PIK3CA gene mutation. Exome sequencing was performed to ~100× average read depth for his two dermatoses, two areas of normal skin, and peripheral blood leukocytes. As expected for non-malignant tissues, the patient's mutation burden in his normal skin and leukocytes was low. He, his mother, and his maternal grandfather carried a heterozygous, germline, in-frame, 24-base-pair deletion in LEMD3. Radiographs of the patient and his mother revealed bony foci consistent with OPK, but she showed no MEL. For the patient, somatic variant analysis, using four algorithms to compare all 20 possible pairwise combinations of his five DNA samples, identified only one high-confidence mutation, heterozygous KRAS Q61H (NM_033360.3:c.183A>C, NP_203524.1:p.Gln61His), in both his dermatoses but absent in his normal skin and blood. Thus, sparing our patient biopsy of his MEL bone, we identified a heterozygous somatic KRAS mutation in his scleroderma-like dermatosis considered a surrogate for MEL. This implicates postzygotic mosaicism of mutated KRAS, perhaps facilitated by germline LEMD3 haploinsufficiency, causing his MEL.

Melorheostosis: a Rare Sclerosing Bone Dysplasia

PURPOSE OF REVIEW

Melorheostosis is a rare sclerosing bone dysplasia that affects both cortical bone and adjacent soft tissue structures in a sclerotomal distribution. In this review, we describe the natural history, radiological features, proposed pathogenesis, and management options for this debilitating condition.

RECENT FINDINGS

Since its first description in 1922, about 400 cases of melorheostosis have been reported, either as single reports or in small case series. Melorheostosis affects the appendicular skeleton more commonly than the axial skeleton and usually presents with lower limb deformity. Diagnosis is based on a combination of clinical and radiological features that help differentiate this condition from other sclerosing bone dysplasias. LEM domain-containing protein 3 (LEMD3) gene mutations have been demonstrated in several familial cases, but these have been more strongly correlated with other hereditary dysplasias, such as osteopoikilosis, and are not thought to be the causative gene for melorheostosis. The exact etiology of classic sporadically occurring melorheostosis remains unknown, with possible causes being somatic LEMD3 mutations, somatic mutations in the bone morphogenetic protein/transforming growth factor-beta pathway, mutations in multiple genes, or other non-genetic causes. Management in recent years has involved nitrogen-containing bisphosphonates in addition to traditional orthopedic surgical approaches and physical therapy. Melorheostosis may present as mixed or atypical osseous involvement in addition to the classically described "dripping candle wax" appearance of hyperostosis. Some patients may have overlap with osteopoikilosis or Buschke-Ollendorff syndrome. In the future, better characterization of genetic and developmental factors predisposing to melorheostosis may lead to the development of targeted therapy for this condition, as well as for more commonly encountered skeletal abnormalities.

The Role of the Nuclear Envelope Protein MAN1 in Mesenchymal Stem Cell Differentiation

Mutations in MAN1, a protein of the nuclear envelope, cause bone phenotypes characterized by hyperostosis. The mechanism of this pro-osteogenic phenotype remains unknown. We increased and decreased MAN1 expression in mesenchymal stem cells (MSC) upon which standard osteogenic and adipogenic differentiation were performed. MAN1 knockdown increased osteogenesis and mineralization. In contrast, osteogenesis remained stable upon MAN1 overexpression. Regarding a mechanism, we found that low levels of MAN1 facilitated the nuclear accumulation of regulatory smads and smads-related complexes, with a concurrently high expression of nuclear β-Catenin. In addition, we found adipogenesis to be decreased in both conditions, although predominantly affected by MAN1 overexpression. Finally, lamin A, a protein of the nuclear envelope that regulates MSC differentiation, was unaffected by changes in MAN1. In conclusion, our studies demonstrated that lower levels of MAN1 in differentiating MSC are associated with higher osteogenesis and lower adipogenesis. High levels of MAN1 only affected adipogenesis. These effects could have an important role in the understanding of the role of the proteins of the nuclear envelope in bone formation. J. Cell. Biochem. 118: 4425-4435, 2017. © 2017 Wiley Periodicals, Inc.

Osteomesopyknosis: a case report and review of sclerosing bone disorders

OBJECTIVE

We present a case of osteomesopyknosis, a nonmalignant sclerosing bone dysplasia of the axial skeleton, with unknown etiology and unknown prevalence.

METHODS

We studied a 49-year-old female who suffered from back and pelvic pain. Her history was obtained, a physical examination performed, and the laboratory results and imaging diagnostics were studied to describe her disease.

RESULTS

A 49-year-old, perimenopausal female suffered excruciating, intermittent, dull back and pelvic pain for 1.5 years. Nonmalignant blastic bone lesions along her spine and pelvis were discovered on computed tomography (CT) and confirmed by magnetic resonance imaging (MRI) and bone scans. Other metabolic/endocrine conditions were ruled out. Her son also has similar symptoms, and corresponding changes were observed on his vertebrae MRI. Both were diagnosed with osteomesopyknosis.

CONCLUSION

Osteomesopyknosis is a rare, autosomal dominant condition characterized by nonmalignant osteosclerosis restricted to the axial skeleton. The disease may produce chronic low-grade back pain in the thoracic and lumbar regions.

Mutation in LEMD3 (Man1) Associated with Osteopoikilosis and Late-Onset Generalized Morphea: A New Buschke-Ollendorf Syndrome Variant

Introduction. Buschke-Ollendorf syndrome (BOS) is an uncommon syndrome characterized by osteopoikilosis and other bone abnormalities, accompanied by skin lesions, most frequently connective tissue nevi. BOS is caused by mutations in the LEMD3 gene, which encodes the inner nuclear membrane protein Man1. We describe a unique case of osteopoikilosis associated with late-onset localized scleroderma and familial LEMD3 mutations. Case Report. A 72-year-old woman presented with adult-onset diffuse morphea and bullous skin lesions. Evaluation revealed multiple hyperostotic lesions (osteopoikilosis) suggestive of BOS. DNA sequencing identified a previously undescribed nonsense mutation (Trp621X) in the LEMD3 gene encoding Man1. Two additional family members were found to have osteopoikilosis and carry the same LEMD3 mutation. Conclusions and Relevance. We report a unique familial LEMD3 mutation in an individual with osteopoikilosis and late-onset morphea. We propose that this constellation represents a novel syndromic variant of BOS.

Population structure of eleven Spanish ovine breeds and detection of selective sweeps with BayeScan and hapFLK

The goals of the current work were to analyse the population structure of 11 Spanish ovine breeds and to detect genomic regions that may have been targeted by selection. A total of 141 individuals were genotyped with the Infinium 50 K Ovine SNP BeadChip (Illumina). We combined this dataset with Spanish ovine data previously reported by the International Sheep Genomics Consortium (N = 229). Multidimensional scaling and Admixture analyses revealed that Canaria de Pelo and, to a lesser extent, Roja Mallorquina, Latxa and Churra are clearly differentiated populations, while the remaining seven breeds (Ojalada, Castellana, Gallega, Xisqueta, Ripollesa, Rasa Aragonesa and Segureña) share a similar genetic background. Performance of a genome scan with BayeScan and hapFLK allowed us identifying three genomic regions that are consistently detected with both methods i.e. Oar3 (150–154 Mb), Oar6 (4–49 Mb) and Oar13 (68–74 Mb). Neighbor-joining trees based on polymorphisms mapping to these three selective sweeps did not show a clustering of breeds according to their predominant productive specialization (except the local tree based on Oar13 SNPs). Such cryptic signatures of selection have been also found in the bovine genome, posing a considerable challenge to understand the biological consequences of artificial selection.

Identification of a novel LEMD3 Y871X mutation in a three-generation family with osteopoikilosis and review of the literature

INTRODUCTION

Osteopoikilosis is a rare and benign autosomal dominant genetic disorder, characterized by a symmetric but unequal distribution of multiple hyperostotic areas in different parts of the skeleton. Recent studies have reported loss-of-function mutations in the LEM domain containing 3 (LEMD3) gene, encoding an inner nuclear membrane protein, as a cause of osteopoikilosis.

METHODS

We investigated LEMD3 gene in a three-generation family from China, with six patients affected with osteopoikilosis. Peripheral blood samples were collected from family members and 100 healthy controls. All exons of the LEMD3 gene and adjacent exon-intron sequences were amplified by PCR and subsequently sequenced.

RESULTS

A novel heterozygous c.2612_2613insA (p.Y871X) mutation in exon 13 of LEMD3 was identified, which resulted in a frame shift predicted to generate a premature stop codon at amino acid position 871. The mutation co-segregates with the osteopoikilosis phenotype and was not found in 100 ethnically matched controls.

CONCLUSION

We identified a new mutation in LEMD3 gene, accounting for the familial case of osteopoikilosis. In addition we also review the clinical manifestation, diagnosis and treatment of osteopoikilosis.

Melorheostosis: segmental osteopoikilosis or a separate entity?

PURPOSE

Melorheostosis is a progressive hyperostotic bone disease that commonly affects the appendicular skeleton. Melorheostosis has a significant degree of overlap with other hyperostosis conditions including osteopoikilosis and likely represent varying degrees of a clinical spectrum.

METHODS

This is a report of 2 patients with melorheostosis who presented with different clinical presentations and involvement of different anatomic locations.

RESULTS

One of the patients presented with foot size asymmetry along with intermittent foot pain and limping. This patient also had irregular nonblanching yellow plaque-like lesion on the forehead. The second patient presented with abnormal gait but no pain. Radiographs demonstrated endosteal hyperostosis, which were consistent with a mixed picture of melorheostosis and osteopoikilois. Genetic testing of the LEMD3 gene from a blood sample was negative in both cases.

CONCLUSIONS

The diagnosis of melorheostosis can be made based on the clinical and radiographic features and can be challenging to differentiate from other hyperostosis conditions.

LEVEL OF EVIDENCE

Level V.

Sclerosing bone dysplasias: leads toward novel osteoporosis treatments

Sclerosing bone dysplasias are a group of rare, monogenic disorders characterized by increased bone density resulting from the disturbance in the fragile equilibrium between bone formation and resorption. Over the last decade, major contributions have been made toward better understanding of the pathogenesis of these conditions. These studies provided us with important insights into the bone biology and yielded the identification of numerous drug targets for the prevention and treatment of osteoporosis. Here, we review this heterogeneous group of disorders focusing on their utility in the development of novel osteoporosis therapies.

Melorheostosis - Case Report of Rare Disease

Introduction:

Melorheostosis(synonyms: candle bone disease, melting wax syndrome, Leri disease) is a rare chronic bone disorder, first described in 1922 by Leri and Joanny. Men and women are equally affected, and no hereditary features have been discovered. Onset is insidious, and most common symptom is pain. Most common part of bone is diaphysis of the long bone of lower limb rarely the axial skeleton. Classical radiological appearance of ’flowing hyperosteosis’ resembling hardened wax that has dripped down the side of a candle.

Case Report:

A 35 years old woman presented with left leg pain with mild swelling and limitation of knee movement. On examination non tender bony heard swelling, hyperpigmented and restriction of knee movement present. Plain radiographs showed extensive, dense, undulating or irregular cortical hyperostosis, resembling candle wax, extending along the length of bone. Pamidronate as well asanalgesic were given to the patient. Physiotherepy started for the deformity.

Conclusion:

Routine laboratory findings usually are normal. The exact cause remain unclear. There is no definite treatment available for this disease. Only symptomatic treatment improve the condition of the patients, more fruitful result obtain with pamidronate and physiotherapy.

Boston type craniosynostosis: report of a second mutation in MSX2

We describe a family that segregated an autosomal dominant form of craniosynostosis characterized by variable expression and limited extra-cranial features. Linkage analysis and genome sequencing were performed to identify the underlying genetic mutation. A c.443C>T missense mutation in MSX2, which predicts p.Pro148Leu was identified and segregated with the disease in all affected family members. One other family with autosomal dominant craniosynostosis (Boston type) has been reported to have a missense mutation in MSX2. These data confirm that missense mutations altering the proline at codon 148 of MSX2 cause dominantly inherited craniosynostosis.

Buschke — Ollendorff syndrome in infant patients

The authors present a clinical and histological description of two clinical cases of a rare inherited disease, Buschke — Ollendorff syndrome. In both cases, the disease was not accompanied by the bone tissue dysplasia but at the same time it was characterized by a clear histological pattern specific of this syndrome. The authors provide literature data and discuss issues related to the pathogenesis and particular features of the clinical picture and diagnostics of the disease.

A novel sclerosing skeletal dysplasia with mixed sclerosing bone dysplasia, characteristic syndromic features, and clinical and radiographic evidence of male-male transmission

We report on a father and his 4-year-old son sharing a characteristic dysmorphic facial phenotype (including hyperteleroism, prominent forehead, and wide nasal bridge), macrocephaly, hearing loss, palatal clefting, developmental delay, hypotonia and bony abnormalities including marked cranial sclerosis and sclerosis of the ribs and long bones, which evolved in severity in the son between the ages of 2 and 4 years. The father's radiographs also showed prominent coarse striations, patchy metaphyseal sclerotic plaques, markedly increased bone density and cortical thickening of long bones, and significant degenerative changes in the thoracic spine. The son has an additional history of sleep apnea resulting from multi-level airway obstruction that includes adenoid hypertrophy, lingual tonsil hypertrophy, subglottic stenosis, and supra-arytenoid tissue consistent with laryngomalacia and tracheomalacia. The clinical, radiographic, and genetic findings in father and son are consistent with a sclerosing skeletal dysplasia syndrome with similarities to mixed sclerosing bone dysplasia (MSBD) including metaphyseal plaques, osteopathia striata, and cranial sclerosis (OS-CS). This family may represent one of the first descriptions of familial inheritance and evolving phenotype in MSBD. The evidence for male-male transmission would support the existence of an autosomal mechanism of inheritance for a novel form of MSBD with characteristic syndromic features.

Connective tissue nevi in children: institutional experience and review

BACKGROUND

Connective tissue nevi (CTN) are circumscribed hamartomas of the skin in which there is an abnormal mixture of normal components of the dermis that may be sporadic or associated with syndromes such as Buschke-Ollendorff, tuberous sclerosis, and Proteus.

OBJECTIVE

We sought to specify the clinical and histologic features of CTN in childhood and to propose a diagnostic approach and updated classification.

METHODS

This was a retrospective study in a tertiary pediatric outpatient population, accessing clinical and histopathological records.

RESULTS

We classified 114 cases of CTN from 1980 to 2008.

LIMITATIONS

The majority of cases were confirmed by histopathological examination. Therefore, our series excludes many CTN that were not biopsied. In addition, follow-up was variable.

CONCLUSION

Our series demonstrates the usefulness of a modified classification for CTN. Biopsy should be done when clinical diagnosis is uncertain, or in multiple lesions. When biopsy is performed it should include normal-appearing skin for comparison and, in Buschke-Ollendorff syndrome, limited anterior-posterior x-rays of the hands, wrists, feet, ankles, knees, and pelvis instead of a full skeletal survey.

Elevated serum lactate dehydrogenase isoenzymes and aspartate transaminase distinguish Albers-Schönberg disease (Chloride Channel 7 Deficiency Osteopetrosis) among the sclerosing bone disorders

Osteopetrosis (OPT) refers to the consequences of generalized failure of skeletal resorption during growth. Most cases are explained by loss-of-function mutation within the genes that encode either chloride channel 7 (CLCN7) or a vacuolar proton pump subunit (TCIRG1), each compromising acid secretion by osteoclasts. Patients suffer fractures and sometimes cranial nerve entrapment and insufficient medullary space for hematopoiesis. In 1996, we reported that a high serum level of the brain isoenzyme of creatine kinase (BB-CK), the CK of osteoclasts, characterizes OPT dueamong the sclerosing bone disorders (J Clin Endocrinol Metab. 1996;11:1438). Now, we show that elevation in serum of multiple lactate dehydrogenase (LDH) isoenzymes with aspartate transaminase (AST) distinguishes autosomal dominant OPT due to loss-of-function mutation in CLCN7 [Albers-Schönberg disease (A-SD)] among these conditions. Serum total LDH and AST levels as high as 3× and 2×, respectively, the upper limits of normal for age-appropriate controls, were persistent and essentially concordant in A-SD. Serum LDH was elevated in 7 of 9 children and in the 2 adults studied with A-SD. LDH isoenzyme quantitation showed excesses of LDH-2, -3, and -4. Neither total LDH nor AST increases were found in other forms of OPT, including bisphosphonate-induced OPT, or in 41 children and 6 adults representing 20 additional sclerosing bone disorders. Serum TRACP-5b and BB-CK also were markedly elevated in A-SD. Hence, high serum levels of several enzymes characterize A-SD. Elevated serum LDH isoenzymes and AST indicate a disturbance (of uncertain clinical significance) within multiple extraosseous tissues when there is CLCN7 deficiency.

Case report: severe melorheostosis involving the ipsilateral extremities

Melorheostosis is a rare, noninheritable bone dysplasia characterized by its classic radiographic feature of flowing hyperostosis resembling dripping candle wax, generally on one side of the long bone. The condition originally was described by Leri and Joanny in 1922. Its etiology remains speculative, and treatment in most instances has been symptomatic. Melorheostosis usually affects one limb, more often the lower extremity, and rarely the axial skeleton. We report a rare case of severe melorheostosis in the ipsilateral upper and lower extremities with normal contralateral extremities. The plain radiographs revealed almost all the bones in the affected extremities, from clavicle and scapula to distal phalanges of the fingers and from femur to distal phalanges of the toes, presented extensive, dense hyperostosis and heterotopic ossification in the periarticular soft tissue. Physical examination showed considerable swelling and deformities of the left limbs, stiffness and distortion of the joints, and anesthesia in the left ulnar regions of the forearm and hand. The examination of the right side was normal. Computed tomography scans showed multiple areas of classic candle wax-like hyperostosis and narrowing or disappearance of the medullary cavity. Histologic analysis confirmed the clinical and imaging diagnosis and revealed extremely dense sclerotic bone of cortical pattern.

Craniofacial melorheostosis

Melorheostosis is a rare benign disease of cortical bone most frequently presenting as peripheral hyperostosis with a characteristic "melting wax" appearance on conventional radiographs. The disease most frequently affects the appendicular skeleton and is seen only rarely in the craniofacial bones. We discuss a case of melorheostosis in the nasal cavity and skull base with an atypical radiographic appearance and suggest findings that may differentiate craniofacial melorheostosis from more common entities in this region.

[(Over-)flowing bone: the rare disease of melorheostosis: clinical presentation and therapeutic concepts demonstrated by three cases]

Melorheostosis is a rare, benign, and sporadically occurring osteosclerosis of unknown cause. The onset of the disease is usually in early adulthood. Melorheostosis affects both genders, develops progressively, and is usually limited to one side of the human body. The sclerosis originates predominantly from the cortices of the long bones of the lower limbs and rarely the upper limbs. Frequently, the sclerosis involves the soft tissue surrounding the affected bones which may cause limitations in the range of motion, contractures, deformities, and pain. Melorheostosis is usually diagnosed by radiograms. Pain relief and restoration of the full range of motion are the primary goals of the therapeutic approach. A good outcome cannot always be achieved and a recurrence of the disease happens very often.

A novel LEMD3 mutation common to patients with osteopoikilosis with and without melorheostosis

Recent studies have reported loss of function mutations in the LEMD3 gene, encoding an inner nuclear membrane protein that influences Smad signaling, as a cause of osteopoikilosis, Buschke-Ollendorff syndrome, and melorheostosis. We investigated LEMD3 in a three-generation family with osteopoikilosis from the Azores, an affected father and daughter from Ireland with osteopoikilosis (the daughter also had melorheostosis), and two other individuals from the UK with isolated melorheostosis. We found a novel C to T substitution at position 2032 bp (cDNA) in exon 8 of LEMD3, resulting in a premature stop codon at amino acid position 678. This mutation co-segregates with the osteopoikilosis phenotype in both the Azorean family and the Irish family. It was not detected in any of the six unaffected family members or in 342 healthy Caucasian individuals. No LEMD3 mutations were detected in the two patients with sporadic melorheostosis. The LEMD3 mutation reported was clearly the cause of osteopoikilosis in the two families but its relationship to melorheostosis in one of the family members is still unclear. Perhaps unsurprisingly in what is a segmental disease, we did not find LEMD3 mutations in peripheral-blood-derived DNA from the two other individuals with sporadic melorheostosis. The nature of the additional genetic and/or environmental influences required for the development of melorheostosis in those with osteopoikilosis requires further investigation.

"Laminopathies": a wide spectrum of human diseases

Mutations in genes encoding the intermediate filament nuclear lamins and associated proteins cause a wide spectrum of diseases sometimes called "laminopathies." Diseases caused by mutations in LMNA encoding A-type lamins include autosomal dominant Emery-Dreifuss muscular dystrophy and related myopathies, Dunnigan-type familial partial lipodystrophy, Charcot-Marie-Tooth disease type 2B1 and developmental and accelerated aging disorders. Duplication in LMNB1 encoding lamin B1 causes autosomal dominant leukodystrophy and mutations in LMNB2 encoding lamin B2 are associated with acquired partial lipodystrophy. Disorders caused by mutations in genes encoding lamin-associated integral inner nuclear membrane proteins include X-linked Emery-Dreifuss muscular dystrophy, sclerosing bone dysplasias, HEM/Greenberg skeletal dysplasia and Pelger-Huet anomaly. While mutations and clinical phenotypes of "laminopathies" have been carefully described, data explaining pathogenic mechanisms are only emerging. Future investigations will likely identify new "laminopathies" and a combination of basic and clinical research will lead to a better understanding of pathophysiology and the development of therapies.

Deactivating germline mutations in LEMD3 cause osteopoikilosis and Buschke-Ollendorff syndrome, but not sporadic melorheostosis

Autosomal dominant OPK and BOS feature widespread foci of osteosclerotic trabeculae without or with skin lesions, respectively. Occasionally, a larger area of dense bone in OPK or BOS resembles MEL, a sporadic sclerosing disorder primarily involving cortical bone. Others, finding deactivating germline LEMD3 mutations in OPK or BOS, concluded such defects explain all three conditions. We found germline LEMD3 mutations in OPK and BOS but not in sporadic MEL.

INTRODUCTION

In 2004, others discovered that heterozygous, loss-of-function, germline mutations in the LEMD3 gene (LEMD3 or MAN1) cause both osteopoikilosis (OPK) and Buschke-Ollendorff syndrome (BOS). OPK is an autosomal dominant, usually benign, skeletal dysplasia featuring multiple, small, especially metaphyseal, oval or round, dense trabecular foci distributed symmetrically throughout the skeleton. BOS combines OPK with connective tissue nevi comprised of collagen and elastin. In some OPK and BOS families, an individual may have relatively large, asymmetric areas of dense cortical bone interpreted as melorheostosis (MEL). MEL, however, classically refers to a sporadic, troublesome skeletal dysostosis featuring large, asymmetric, "flowing hyperostosis" of long bone cortices often with overlying, constricting soft tissue abnormalities. However, a heterozygous germline mutation in LEMD3 was offered to explain MEL.

MATERIALS AND METHODS

We studied 11 unrelated individuals with sclerosing bone disorders where LEMD3 mutation was a potential etiology: familial OPK (1), familial BOS (2), previously reported familial OPK with MEL (1), sporadic MEL (3), sporadic MEL with mixed-sclerosing-bone dystrophy (1), and patients with other unusual sclerosing bone disorders (3). All coding exons and adjacent mRNA splice sites for LEMD3 were amplified by PCR and sequenced using genomic DNA from leukocytes. We did not study lesional tissue from bone or skin.

RESULTS

In the OPK family, a heterozygous nonsense mutation (c.1433T>A, p.L478X) was discovered in exon 1. In the two BOS families, a heterozygous nonsense mutation (exon 1, c.1323C>A, p.Y441X) and a heterozygous frame-shift mutation (exon 1, c.332_333insTC) were identified. In the individual with MEL and familial OPK, a heterozygous nonsense mutation (c.1963C>T, p.R655X) was detected in exon 7. However, no LEMD3 mutation was found for any other patient, including all four with sporadic MEL.

CONCLUSIONS

We confirm that OPK and BOS individuals, including those with MEL-like lesions, have heterozygous, deactivating, germline LEMD3 mutations. However, MEL remains of unknown etiology.