Reduced expression of semaphorin 3A in osteoclasts causes lymphatic expansion in a Gorham-Stout disease (GSD) mouse model

Gorham-Stout disease (GSD) is a sporadic chronic disease characterized by progressive bone dissolution, absorption, and disappearance along with lymphatic vessel infiltration in bone-marrow cavities. Although the osteolytic mechanism of GSD has been widely studied, the cause of lymphatic hyperplasia in GSD is rarely investigated. In this study, by comparing the RNA expression profile of osteoclasts (OCs) with that of OC precursors (OCPs) by RNA sequencing, we identified a new factor, semaphorin 3A (Sema3A), which is an osteoprotective factor involved in the lymphatic expansion of GSD. Compared to OCPs, OCs enhanced the growth, migration, and tube formation of lymphatic endothelial cells (LECs), in which the expression of Sema3A is low compared to that in OCPs. In the presence of recombinant Sema3A, the growth, migration, and tube formation of LECs were inhibited, further confirming the inhibitory effect of Sema3A on LECs in vitro. Using an LEC-induced GSD mouse model, the effect of Sema3A was examined by injecting lentivirus-expressing Sema3A into the tibiae in vivo. We found that the overexpression of Sema3A in tibiae suppressed the expansion of LECs and alleviated bone loss, whereas the injection of lentivirus expressing Sema3A short hairpin RNA (shRNA) into the tibiae caused GSD-like phenotypes. Histological staining further demonstrated that OCs decreased and osteocalcin increased after Sema3A lentiviral treatment, compared with the control. Based on the above results, we propose that reduced Sema3A in OCs is one of the mechanisms contributing to the pathogeneses of GSD and that expressing Sema3A represents a new approach for the treatment of GSD.

Abnormalities in C-type lectin-like receptor 2 in a patient with Gorham-Stout disease: the first case report

Background

Gorham-Stout disease (GSD) is a form of lymphangiomatosis of unknown etiology, characterized by abnormal distribution of lymphatic vessels. Platelets and lymphangiogenesis are closely related via C-type lectin-like receptor 2 (CLEC-2)/podoplanin.

Key Clinical Question

Despite similarities between abnormal lymphatic vessels in CLEC-2-deficient mice and patients with GSD, whether CLEC-2 on platelets is involved in GSD pathogenesis is unknown.

Clinical Approach

We examined CLEC-2 expression in platelets of a patient with lethal GSD. Most of the patient's platelets expressed aberrant CLEC-2 that was not detectable by certain monoclonal antibodies for human CLEC-2. Further, this population was not activated by a CLEC-2-activating snake venom, rhodocytin. Possible causes of abnormal CLEC-2 including anti-CLEC-2 autoantibodies, podoplanin binding to CLEC-2, and pathogenic CLEC1B gene alteration were excluded.

Conclusions

We believe that this is the first report of a patient with structurally and functionally abnormal CLEC-2. CLEC-2 abnormality may be associated with dysregulated lymphangiogenesis in GSD.

Trametinib inhibits lymphatic vessel invasion of bone in a mouse model of Gorham-Stout disease

Objective

Gorham-Stout disease (GSD) is a rare lymphatic anomaly that can be caused by somatic activating mutations in KRAS. This discovery has led investigators to suggest that MEK inhibitors could be a novel treatment for GSD. However, the effect of MEK inhibitors on bone disease in animal models of GSD has not been investigated. We recently reported that Osx-tTA;TetO-Vegfc mice exhibit a phenotype that resembles GSD. Osx-tTA;TetO-Vegfc mice overexpress VEGF-C in bone, which stimulates the development of lymphatic vessels in bone and the gradual loss of cortical bone. The objective of this study was to characterize the effect of trametinib, an FDA-approved MEK1/2 inhibitor, on lymphangiogenesis and osteolysis in Osx-tTA;TetO-Vegfc mice.

Methods

Immunoblotting was performed to assess the effect of trametinib on VEGF-C-induced phosphorylation of ERK1/2, AKT, and S6 in primary human lymphatic endothelial cells (LECs). Prevention and intervention experiments were performed to determine the effect of trametinib on lymphangiogenesis and osteolysis in Osx-tTA;TetO-Vegfc mice.

Results

We found that trametinib blocked VEGF-C-induced phosphorylation of ERK1/2 in primary human LECs. We also found that trametinib prevented VEGF-C-induced lymphatic invasion of bone and cortical bone loss in Osx-tTA;TetO-Vegfc mice. Additionally, trametinib slowed the progression of disease in Osx-tTA;TetO-Vegfc mice with established disease. However, it did not reverse disease in Osx-tTA;TetO-Vegfc mice.

Conclusion

Our results show trametinib impacts bone disease in Osx-tTA;TetO-Vegfc mice. These findings further support the testing of MEK inhibitors in patients with GSD and other RAS pathway-driven complex lymphatic anomalies with bone involvement.

Hyperactive KRAS/MAPK signaling disrupts normal lymphatic vessel architecture and function

Complex lymphatic anomalies (CLAs) are sporadically occurring diseases caused by the maldevelopment of lymphatic vessels. We and others recently reported that somatic activating mutations in KRAS can cause CLAs. However, the mechanisms by which activating KRAS mutations cause CLAs are poorly understood. Here, we show that KRASG12D expression in lymphatic endothelial cells (LECs) during embryonic development impairs the formation of lymphovenous valves and causes the enlargement of lymphatic vessels. We demonstrate that KRASG12D expression in primary human LECs induces cell spindling, proliferation, and migration. It also increases AKT and ERK1/2 phosphorylation and decreases the expression of genes that regulate the maturation of lymphatic vessels. We show that MEK1/2 inhibition with the FDA-approved drug trametinib suppresses KRASG12D-induced morphological changes, proliferation, and migration. Trametinib also decreases ERK1/2 phosphorylation and increases the expression of genes that regulate the maturation of lymphatic vessels. We also show that trametinib and Cre-mediated expression of a dominant-negative form of MEK1 (Map2k1 K97M) suppresses KRASG12D-induced lymphatic vessel hyperplasia in embryos. Last, we demonstrate that conditional knockout of wild-type Kras in LECs does not affect the formation or function of lymphatic vessels. Together, our data indicate that KRAS/MAPK signaling must be tightly regulated during embryonic development for the proper development of lymphatic vessels and further support the testing of MEK1/2 inhibitors for treating CLAs.

A case of liposarcoma with osteolysis of the maxilla as the first symptom and review of the literature

Liposarcomas are extremely rare in the oral cavity and mainly observed in the buccal mucosa, tongue, floor of the mouth, gingiva, and lips, while those occurring in the jaws have not been reported so far. Clinically, the initial presentation of liposarcoma is usually a painless soft tissue mass. The aim of this study was to report a case of liposarcoma with osteolysis of the maxilla as the first symptom, and review the relevant literature to summarize its clinical features, imaging features, pathological features and treatment methods.

Gorham-Stout disease affecting the spine with cerebrospinal fluid leakage and Chiari-like tonsillar herniation: a rare case report and review of literature

BACKGROUND

Gorham-Stout disease (GSD) is a very rare disorder characterized by massive osteolysis of poorly understood aetiology. The association between GSD involving the skull base and cerebrospinal fluid (CSF) leakage has been reported in the literature. However, few cases of CSF leakage and Chiari-like tonsillar herniation in GSD involving the spine have been reported.

CASE PRESENTATION

We present the case of a 20-year-old man with GSD involving the thoracic and lumbar spine, which caused CSF leakage and Chiari-like tonsillar herniation. The patient underwent four spinal surgeries for osteolytic lesions of the spine over a 10-year period. Here, we discuss the possible aetiology of the development of CSF leakage. Epidural blood patch (EBP) was performed at the T11-T12 level to repair the CSF leakage. After EBP treatment, rebound intracranial hypertension (RIH) developed, and tonsillar herniation disappeared 2 months later.

CONCLUSIONS

GSD involving the spine with CSF leakage and Chiari-like tonsillar herniation is relatively rare. For patients who have undergone multiple spinal surgeries, minimally invasive treatment is an alternative treatment for CSF leakage. EBP can repair CSF leakage secondary to GSD and improve chronic brain sagging, with reversibility of Chiari-like malformations.

Complex Lymphatic Anomalies: Report on a Patient Registry Using the Latest Diagnostic Guidelines

Objective: Generalized lymphatic anomaly (GLA), Gorham-Stout disease (GSD), kaposiform lymphangiomatosis (KLA), and central conducting lymphatic anomaly (CCLA) are rare, multisystem lymphatic disorders, referred to as complex lymphatic anomalies (CLAs). Their etiology remains poorly understood; however, somatic activating mutations have recently been discovered, and the results of targeted treatments are promising. This study aimed to elaborate on the phenotypic description of CLA. Methods: Thirty-six consecutive patients were recruited for the "GLA/GSD Registry" of the University Hospital of Freiburg, Germany (2015-2021). Clinical data were prospectively collected provided that a signed informed consent form was obtained. The latest proposed diagnostic guidelines were retrospectively applied. Results: Thirty-two patients (38% males) were included in the study; 15 GLA, 10 GSD, 3 KLA, and 4 CCLA patients were identified. Eighty-four percent already had symptoms by the age of 15 years. Osteolysis and periosseous soft-tissue infiltration were associated with GSD (p < 0.001 and p = 0.011, respectively), ascites and protein-losing enteropathy with CCLA (p = 0.007 and p = 0.004, respectively), and consumption coagulopathy with KLA (p = 0.006). No statistically significant differences were found in organ involvement, distribution of osteolytic lesions, number of affected bones and fractures. Twenty-five patients had complications; one patient with GLA died despite multimodal treatment. Spontaneous regression was seen in one patient with untreated KLA. Conclusions: CLA are rare, and their overlapping clinical presentations make differential diagnosis difficult. The characterization of our case series contributes to the phenotypic description and differentiation of these four clinical entities. A further understanding of their pathogenesis is crucial for evaluating targeted therapies and optimizing medical care.

Diagnostic Dilemma of Vanishing Bone Disease - A Case Report and Review of Literature

Rationale

Vanishing bone disease (VBD) is a rare bone disorder in which progressive osteolysis may lead to complete disappearance of involved bones. The diagnosis of this disease requires a high degree of clinical suspicion. We present a case of progressive osteolysis of mandible in a patient.

Patient Concerns

The patient had been without definitive diagnosis and treatment for over a year.

Diagnosis

Diagnosis was made by exclusion of genetic, traumatic, inflammatory, infective, endocrine and neoplastic aetiologies and by carefully correlating clinical, imaging and histopathological findings of the patient.

Treatment

Segmental resection of the advancing edge of the lesion was carried out.

Outcome

The patient is disease free, with no evidence of further osteolysis, after six months of follow-up.

Take-Away Lessons

This article describes the exclusion-based approach adopted to diagnose a case of VBD, aiming to standardise a workup for the diagnosis.

Clinical and radiological improvement in Gorham-Stout disease after sirolimus treatment

BACKGROUND

Gorham-Stout disease (GSD) is a rare syndrome characterized by lymphatic malformations, mainly in bone structures, causing progressive osteolysis. Lymphatic endothelial cell proliferation depends on several growth factors that use the phosphoinositide-3 kinase (PI3K)/Akt pathway and converge on the mammalian target molecule of the rapamycin (mTOR) pathway. These findings have allowed treating GSD with mTOR pathway inhibitors such as sirolimus or everolimus.

CASE REPORT

We present the case of a one-year-old female patient referred to our institution after a right femur fracture and progressive limb volume increase, disproportionately to the trauma. After several episodes of soft tissue infections, imaging studies showed pseudarthrosis, lytic lesions, and progressive loss of the right femur that ended in total absence. A femur biopsy showed lymphatic structures positive with D2-40 staining, diagnosing GSD. After six months of non-response to traditional treatments, the limb was disarticulated at the hip level, and oral sirolimus treatment was initiated, showing clinical and radiological improvement with minor lytic lesions and evidence of ossification after 20 months of treatment.

CONCLUSIONS

Oral sirolimus treatment for GSD inhibits angiogenesis and osteoclastic activity, stimulating bone anabolism and leading to arrested osteolysis progression and improved ossification, quality of life, and patient prognosis. Therefore, sirolimus should be considered a therapeutic option for this rare disease.

How we approach the diagnosis and management of complex lymphatic anomalies

Complex lymphatic anomalies (CLA) are congenital diseases of the lymphatic circulation system that are associated with significant morbidity and early mortality. While guidelines for the comprehensive evaluation of the CLA were recently published, the diagnostic approach and medical management are not standardized. This article presents the clinical features of four CLA: Gorham-Stout disease, generalized lymphatic anomaly, kaposiform lymphangiomatosis, and central collecting lymphatic anomaly. We also offer three cases from the authors' practice and our views on diagnostic testing and disease management including supportive care, medical therapies, and other interventions.

Gorham-Stout disease of skull base leading to cranial settling and rhinorrhea: a case-based review

PURPOSE

Gorham-Stout disease (GSD) is a rare progressive osteolytic disorder, theoretically caused by lymphovascular endothelial proliferation. Spinal involvement carries a dismal prognosis because of neurological consequences. Lesions of the skull base are extremely rare and entail even more devastating prognosis due to cervical instability and cerebrospinal fluid (CSF) leakage. Due to scarcity of this condition, the aim of this study was to give an overview of skull base GSD and review the cases with such condition reported in the literature.

METHODS

In this case-based review, different aspects of skull base GSD are discussed, and a sample clinical case of GSD leading to cranial settling and rhinorrhea is presented. The characteristics, symptoms, and managements of all English-language PubMed-reported cases were reviewed, and different features of presentation and methods of treatments were analyzed.

RESULTS

Based on the literature review, most of the cases encountered serious problems in the course of the disease. Meningitis/CSF leakage was detected in 12 of 26 collected cases, followed by hearing loss/tinnitus/otitis media in 10 cases, headache in 8, and neck pain/stiffness in 8 patients. Despite a variety of treatments, improvement was only observed in 8 of 26 collected cases. The reminders showed either stable condition or worsening and death.

CONCLUSION

All cases of GSD of the skull base should be evaluated for rhinorrhea/otorrhea and cranial settling, both of them being among the most life-threatening conditions. Since definite treatment, in order to stop disease progression, is sometimes impossible, symptomatic and supportive treatment should be started as possible.

Bacterial meningitis due to the Streptococcus mitis group in children with cerebrospinal fluid leak

The Streptococcus mitis group constitutes a part of the oral flora in humans and has been reported to cause infective endocarditis, brain abscesses, sepsis, pneumonia, and peritonitis. However, the S. mitis group rarely causes meningitis in children. We experienced a case of bacterial meningitis due to the S. mitis group in a 14-year-old girl with Gorham-Stout disease undergoing treatment with sirolimus for skull base osteolysis and cerebrospinal fluid (CSF) leak. Antibiotic treatment was initiated with linezolid and levofloxacin due to allergies against β-lactam antibiotics. On the third treatment day, antibiotics were switched to penicillin G according to CSF culture results, which were positive for penicillin-susceptible S. mitis group. Antibiotic therapy was successfully completed after 14 days without any neurological sequelae. There have apparently been no reports of S. mitis meningitis in pediatric patients with skull base osteolysis and CSF leak as in our case. Our findings suggest that clinicians should be aware of the possibility of S. mitis meningitis for patients with skull base osteolysis and/or CSF leakage.

[Unilateral subjective tinnitus «vanishing bone» disease (Goram-Stout syndrome).]

The article presents the case history of an 11-year-old girl with Goram-Stout disease, who debuted with unilateral subjective tinnitus. A review of the literature, cases with damage of the temporal bones and modern methods of treatment of this disease is made.

Stimulation of Treg Cells to Inhibit Osteoclastogenesis in Gorham-Stout Disease

Gorham-Stout disease (GSD) is a very rare syndrome displaying excessive bone erosion and vascular lesion. Due to the rarity of the disease and to the limited studies, its etiopathogenesis is not entirely known. The involvement of immune system in the progressive osteolysis was recently suggested. Indeed, extensive reciprocal interactions between the immune and skeletal systems have been demonstrated. This study aimed to evaluate alterations of immune cells in GSD. An increase of CD8+ cells and reduction of CD4+ and CD4+CD25+CD127^low cells was revealed in patients. Interestingly, patients’ regulatory T cells maintain the ability to respond to extracellular stimuli and to regulate osteoclastogenesis; GSD cells proliferate under aCD3/CD28 signal reaching similar levels to those observed in control culture and exert their immunomodulatory activity on effector T cells. GSD Treg cells preserved their inhibitory effects on the osteoclastogenesis. These results suggest that stimulation of Treg cells could open the way for the identification and testing of new therapeutic approaches for patients affected by GSD.

CT and MRI Findings of Focal Splenic Lesions and Ascites in Generalized Lymphatic Anomaly, Kaposiform Lymphangiomatosis, and Gorham-Stout Disease

Objectives:

This study aimed to evaluate the CT and MRI findings of focal splenic lesions and ascites in generalized lymphatic anomaly (GLA), kaposiform lymphangiomatosis (KLA), and Gorham-Stout disease (GSD).

Material and Methods:

Twenty-three patients (10 with GLA, 5 with KLA, and 8 with GSD) who underwent abdominal CT and/or MRI before treatment were included in this study, and their imaging findings were retrospectively evaluated.

Results:

Focal splenic lesions were observed in nine patients; these lesions were observed frequently in GLA (n = 5; 50%) or KLA (n = 3; 60%) compared with GSD (n = 1; 13%); however, no significant differences were found between the three groups (P = 0.190). On CT images among eight patients (4 with GLA, 3 with KLA, and 1 with GSD) with focal splenic lesions who underwent CT, the number of focal splenic lesions per patient ranged from 2 to 189 (mean, 42) and the maximum diameter of focal splenic lesions ranged from 2 to 39 mm (mean, 8 mm), while more than 30 focal splenic lesions per patient were observed in 2 (50%) GLA and focal splenic lesions with maximum diameters of ≥10 mm were observed in 4 (100%) GLA but not in KLA or GSD. Ascites was observed in five patients; significant differences were observed among KLA (n = 4; 80%), GLA (n = 1; 10%), and GSD (n = 0; 0%) (P < 0.01). Ascites was significantly more frequent in KLA than in GSD (P < 0.05).

Conclusion:

More than 30 focal splenic lesions per patient and/or focal splenic lesions with maximum diameters of ≥10 mm were observed only in GLA. Focal splenic lesions tended to be less frequent in GSD, whereas ascites tended to be frequent in KLA.

A Case of Gorham-Stout Disease Treated with Fistula Closure by Transmeatal Approach

Gorham-Stout disease, a rare and intractable disease of unknown etiology, causes systemic bone lysis and replacement with lymphoid tissue. Here, we report a case of Gorham-Stout disease with cerebrospinal fluid leakage in a 16-year-old boy. The patient complained of nasal discharge, right ear obstruction, fever, and headache. A computed tomography scan of the head showed osteolysis around the right internal carotid artery, vestibule, and cochlea and osteolytic changes in the left parietal bone. It was suggested that the patient had bacterial meningitis owing to the leakage of cerebrospinal fluid from the fistula caused by the temporal bone osteolysis. He was treated with meropenem, and a transmeatal fistula closure and a bone biopsy of the left parietal bone were performed. Intraoperatively, osteolysis was observed on the promontory and around the internal carotid artery. The fistula was closed by dense filling and compression around the fistula, in the middle ear cavity, and in the external auditory canal. The symptoms disappeared after the surgery. Bone biopsy showed the presence of a lymphangioma, and Gorham-Stout disease was diagnosed. Prophylactic bisphosphonate therapy was initiated. A 4-year follow-up revealed no progression of the disease.

Dysregulated miRNAs in bone cells of patients with Gorham-Stout disease

Gorham-Stout disease (GSD) is a very rare disease characterized by increased bone erosion with angiomatous proliferation. The mechanisms underlying this disorder have not been deeply investigated. Due to its rarity, no guidelines are currently available for treatment and management of GSD. We recently evaluated the cellular alterations of the bone remodeling in patients showing that osteoclast precursors displayed increased ability to differentiate into osteoclasts and that affected osteoclasts resorb bone more actively than control cells. Moreover, osteoblasts isolated from a patient showed a defective ability to form mineralized nodules. In this paper, we investigated the molecular pathways involved in the cellular defects of GSD bone cells. For this study, we recruited nine patients and performed miRNome analysis of bone cells. Between the 178 miRNAs robustly expressed in GSD osteoclasts, significant modulation of three miRNAs (miR-1246, miR-1-3p, and miR-137-3p) involved in the regulation of osteoclast formation and activity or in the angiomatous proliferation was found in patients' cells. Interestingly, miR-1246 was also up-regulated in serum exosomes from patients. Analysis of miRNAs from patient osteoblasts suggested alteration of miR-204a-5p, miR-615-3p and miR-378a-3p regulating osteoblast function and differentiation. The resulting miRNA pattern may help to understand better the mechanisms involved in GSD and to identify new potential therapeutic targets for this rare disease.

Gorham-Stout Disease with Multiple Bone Involvement-Challenging Diagnosis of a Rare Disease and Literature Review

Gorham-Stout disease is a rare disorder, which may result in a poor prognosis. This disease, a rare lymphangiomatosis, is defined by progressive bone disappearance due to massive unicentric and multicentric osteolysis. Osteolytic lesions of the spine and pleura effusion are poor prognostic factors. Herein, we will present a case where the onset of disease occurred at the age of 18 with asthenia, myalgia, and major bone pain, followed by incomplete motor deficiency in the lower limbs and, later, in the upper limbs. Imaging studies (CT scan and MRI) of the patient revealed osteolytic lesions (cervical and thoracic vertebrae, rib, and clavicle) and a pathological fracture of the C7 vertebra. Surgical procedures undertaken involved replacing the affected vertebrae with bone grafting and prosthesis. The investigations performed allowed for the exclusion of inflammation, thyroid or parathyroid disease, lymphoma, neoplasia, or autoimmune disorders. A bone marrow biopsy showed osteolysis, the replacement of bone tissues with connective tissue, and chronic non-specific inflammation. The evolution was negative with almost complete osteolysis of the left clavicle, the emergence of new osteolysis areas in the lumbar vertebrae, pelvic bones, and the bilateral proximal femur, splenic nodules, chylothorax, and associated major neurological deficits. Unfortunately, this negative evolution resulted in the patient’s death a year after onset.

Gorham-Stout disease of the spine presenting with intracranial hypotension and cerebrospinal fluid leak: A case report and review of the literature

Background:

Gorham-Stout (GS) disease or “vanishing bone disease” is rare and characterized by progressive, spontaneous osteolysis resulting in loss of bone on imaging studies. Treatment modalities include combinations of medical and/or surgical treatment and radiation therapy.

Case Description:

A 14-year-old female with GS disease presented with a 1-year history of thoracic back pain and atypical headaches consistent with intracranial hypotension. Magnetic resonance imaging and operative findings demonstrated a spontaneous thoracic cerebrospinal fluid leak (CSF) (e.g., that extended into the pleural cavity) and complete osteolysis of the T9-10 posterior bony elements (e.g., including the rib head, lamina, and transverse processes). The patient underwent repair of CSF fistula followed by a T6-11 instrumented fusion.

Conclusion:

This case of GS disease, involving a thoracic CSF fistula and absence/osteolysis of the T9-T10 bony elements, could be successfully managed with direct dural repair and an instrumented T6-T11 fusion.

Gorham-Stout disease successfully treated with sirolimus (rapamycin): a case report and review of the literature

BACKGROUND

Gorham-Stout disease (GSD) is a rare disease characterized by bone lesions and osteolysis. Therapy usually involves surgical resection. Sirolimus (Rapamycin) is used in some patients with GSD but the efficacy and safety of Sirolimus remains unclear. We propose that Sirolimus may be a novel therapeutic for GSD and present a case and review of literature that supports this.

CASE PRESENTATION

We presented a 1-year-old boy with GSD involving osteolysis of the right humerus with fracture of the left femur complicated by an effusion in the right pleural cavity. X-rays showed osteolysis in the right clavicle. A large pleural effusion was observed on the right-side, and the left lung was significantly compressed. X-rays also showed a fracture of the left femur. A femoral biopsy was performed that showed necrotic tissue in the cortical bone and a large number of irregularly shaped capillaries that proliferated within the necrotic tissue. Dilated lymphatic vessels were seen adjacent to the cortex, with fibrous tissue hyperplasia. We prescribed sirolimus, which is an oral mTOR inhibitor, for two consecutive years. The boy recovered well without other progressive bone lesions and participates in normal daily activities. His growth and development are the same as that of his peers.

DISCUSSION AND CONCLUSION

Gorham-Stout disease is a rare and enigmatic disease characterized by the presentation of an intraosseous lymphatic anomaly (LM), which results in progressive bone resorption. Based on this case report and a literature review, we conclude that sirolimus may be an effective alternative medication for GSD.

Lymphatics in bone arise from pre-existing lymphatics

Bones do not normally have lymphatics. However, individuals with generalized lymphatic anomaly (GLA) or Gorham-Stout disease (GSD) develop ectopic lymphatics in bone. Despite growing interest in the development of tissue-specific lymphatics, the cellular origin of bone lymphatic endothelial cells (bLECs) is not known and the development of bone lymphatics has not been fully characterized. Here, we describe the development of bone lymphatics in mouse models of GLA and GSD. Through lineage-tracing experiments, we show that bLECs arise from pre-existing Prox1-positive LECs. We show that bone lymphatics develop in a stepwise manner where regional lymphatics grow, breach the periosteum and then invade bone. We also show that the development of bone lymphatics is impaired in mice that lack osteoclasts. Last, we show that rapamycin can suppress the growth of bone lymphatics in our models of GLA and GSD. In summary, we show that bLECs can arise from pre-existing LECs and that rapamycin can prevent the growth of bone lymphatics.

A case report of Gorham-Stout disease diagnosed during the course of recurrent meningitis and cholesteatoma

Background

Gorham-Stout disease is a rare bone disorder. Here, we present a case of Gorham-Stout disease diagnosed during follow-up of a patient with cholesteatoma; the disease affected the temporal bone and other sites of the skull. To the best of our knowledge, this is the first report of Gorham-Stout disease diagnosed with recurrent cerebrospinal leakage after surgery to treat cholesteatoma.

Case presentation

A 25-year-old male patient re-presented to our department for the first time in 7 years with otorrhea in the right ear and recurrent meningitis. The patient had a history of multiple surgeries for cholesteatoma and suffered from recurrent cerebrospinal fluid leakage, which initially was thought to be caused by recurrence of cholesteatoma. Therefore, skull base reconstruction was planned. However, the underlying cause was identified eventually as defects in the temporal bone caused by massive osteolysis due to Gorham-Stout disease. Skull base reconstruction was abandoned because the osteolysis was considered to be progressive. Conservative treatment with infectious control was implemented as an alternative.

Conclusion

This case describes unusual temporal bone osteolysis after cholesteatoma surgery and the importance of considering the possibility of multiple concurrent diseases in such individuals. The distinguishing features of this case are the fact that the temporal bone had disappeared, and deconstruction was complicated by infection and inflammation caused by cholesteatoma, surgical invasion, and Gorham-Stout disease. Appropriate diagnosis saved the patient from ineffective multiple surgeries for cerebrospinal fluid leakage or cholesteatoma, and improved his quality of life.

Gorham-Stout disease with parietal bone osteolysis: a case series and review of literature

BACKGROUND

Gorham-Stout disease (GSD) is a rare and idiopathic bone disorder, characterized by massive osteolysis. To date, there is no established treatment strategy for GSD. We empirically treated two patients, who had presented to us with cranial lesions of GSD. Here, we propose a novel algorithm for the management of Gorham's disease based on our experience and review the literature published to date.

METHODS

We reviewed all existing literature on GSD describing the pathophysiology and suggested treatment methods, up to 2018.

RESULTS

We found 13 papers with 14 reported cases; an inclusion of our two cases brings the total count up to just 16 recorded cases of GSD involving the skull. Of these, the base of the skull was affected in eight cases, while the remaining eight cases showed cranial involvement. The patients with skull-base involvement were managed conservatively, using medications or radiotherapy. The patients with cranial osteolysis were managed surgically, with an excision of the osteolytic portion, followed by cranioplasty. Of the latter group, the pericranium was not removed in one patient, in whom a very slight progression of the osteolytic process was later observed.

CONCLUSIONS

The pathogenesis of GSD remains poorly understood. Further study is required to determine an optimum management strategy. A long-term follow-up will also be necessary to establish the effectiveness of the treatment process. The untreated patients show a progressive resorption of the affected bones of the skull. A painful, vanishing skull deformity is an alarming sign of GSD. Early diagnosis and treatment are necessary to arrest disease progression and to prevent complications.

A Child with Early-Onset Gorham-Stout Disease Complicated by Chylothorax: Near-Complete Regression of Bone Lesions with Interferon and Bisphosphonate Treatment

We report a case of Gorham-Stout disease (GSD) complicated by chylothorax and treated with a combination therapy with interferon and bisphosphonates. This treatment may be helpful in improving the usually unfavorable prognosis of GSD beginning with a chylothorax before 1 year of age, and in reducing bone lesions. Moreover, the use of bisphosphonates appears to be useful in treating pain.

Multifocal Gorham-Stout disease associated with Chiari I malformation and recurrent aseptic meningitis: Case report and review of literature

Gorham-Stout disease is a rare condition of uncertain aetiology characterised by lymphatic proliferation within osseous structures and subsequent massive osteolysis. This report describes the index case of a patient with multifocal Gorham-Stout disease involving the skull base with Chiari I malformation and recurrent aseptic meningitis without fistula. A five-year-old male presented following decompression of a Chiari I malformation with headaches, vomiting, and stiff neck and cerebrospinal fluid pleocytosis without growth of a pathogenic organism. Ongoing symptoms prompted a further three presentations over several months revealing persistent aseptic cerebrospinal fluid monocytic pleocytosis. Further investigation revealed multifocal osseous cystic disease and subsequent bone biopsy suggested Gorham-Stout disease. Suboccipital decompression was not repeated despite craniocervical junction re-stenosis. A literature review demonstrated the extreme rarity of Gorham-Stout disease associated with Chiari I malformation and meningitis. Potential mechanisms of these entities occurring in concert are discussed. Consideration of Gorham-Stout disease as a secondary cause for Chiari I malformation is important amid local bone changes or cerebrospinal fluid leakage prior to pursuing suboccipital decompression considering the poor outcomes reported.

Bone development and fracture healing is normal in mice that have a defect in the development of the lymphatic system

Ectopic lymphatics form in bone and promote bone destruction in diseases such as Gorham-Stout disease, generalized lymphatic anomaly, and kaposiform lymphangiomatosis. However, the role lymphatics serve in normal bone development and repair is poorly understood. The objective of this study was to characterize bone development and fracture healing in mice that have a defect in the development of the lymphatic vasculature. We found that bones in wild-type adult mice and mouse embryos did not have lymphatics. We also found that bone development was normal in Vegfr3 (Chy/Chy) embryos. These mice do not have lymphatics and die shortly after birth. To determine whether lymphatics serve a role in postnatal bone development and fracture healing, we analyzed bones from Vegfr3 (wt/Chy) mice. These mice are viable and have fewer lymphatics than wild-type mice. We found that postnatal bone development and fracture healing was normal in Vegfr3 (wt/Chy) mice. Taken together, our results suggest that lymphatics do not play a major role in normal bone development or repair.

Dissecting the mechanisms of bone loss in Gorham-Stout disease

Gorham-Stout disease (GSD) is a rare disorder characterized by progressive osteolysis and angiomatous proliferation. Since the mechanisms leading to bone loss in GSD are not completely understood, we performed histological, serum, cellular and molecular analyses of 7 patients. Increased vessels, osteoclast number and osteocyte lacunar area were revealed in patients' bone biopsies. Biochemical analysis of sera showed high levels of ICTP, Sclerostin, VEGF-A and IL-6. In vitro experiments revealed increased osteoclast differentiation and activity, and impaired mineralization ability of osteoblasts. To evaluate the involvement of systemic factors in GSD, control cells were treated with patients' sera and displayed an increase of osteoclastogenesis, bone resorption activity and a reduction of osteoblast function. Interestingly, GSD sera stimulated the vessel formation by endothelial cells EA.hy926. These results suggest that bone cell autonomous alterations with the cooperation of systemic factors are involved in massive bone loss and angiomatous proliferation observed in GSD patients.

Gorham-Stout disease of the malleolus: a rare case report

Background

Gorham-Stout disease, also known as vanishing bone disease, idiopathic massive osteolysis, is a rare entity of unknown etiopathology. This disease is characterized by destruction of osseous matrix and proliferation of lymphatic vascular structures and associated with massive regional osteolysis. It has a variable clinical presentation and is commonly considered as a benign disease with a progressive tendency and an unpredictable prognosis. The diagnosis is made by exclusion and based on combination with histological, radiological, and clinical features. Despite that several therapeutic options have shown certain efficacy, the effective treatment still remains controversial and there is no standard treatment to be recommended.

Case presentation

A previously healthy 40-year-old man presented with right lateral malleolus pain after an ankle sprain and was referred to our hospital. The radiographs indicated rapid massive bone destruction in the distal right lateral malleolus with an unclear margin. Based on the combination with histological, radiological, and clinical features, the diagnosis of Gorham-Stout disease was made. Considering that the residual function of malleolus had to be protected, prior bisphosphonate was used to control the progression of lesion, followed by surgical resection and biological reconstruction with autologous fibular bone grafting. The patient was followed up 8 years after surgery, he presented without progression and recurrence.

Conclusions

We depict a case of Gorham-Stout disease at the right lateral malleolus and was successfully controlled by medication and surgical intervention. Based on the prior effective medical treatment, resection with biological reconstruction is a useful approach to treat Graham-Stout disease in bone.

Gorham-Stout disease in the rib and thoracic spine with spinal injury treated with radiotherapy, zoledronic acid, vitamin D, and propranolol: A case report and literature review

Gorham-Stout disease (GSD) is a rare bone condition that is characterized by the spontaneous, idiopathic and progressive proliferation of blood or lymphatic vessels, which replace the bone and marrow space. The precise etiology and pathophysiology of GSD remain poorly understood. Therefore, there is no consensus on the treatment of this disease. In the current study, a rare case of GSD in the rib and thoracic spine with spinal injury that was treated with radiotherapy, zoledronic acid, vitamin D and propranolol, is reported. A 77-year-old man visited the hospital complaining of constipation for 10 days. Within a few days, the patient had recognized complete paralysis of the bilateral lower legs. Radiologically, large osteolytic lesions were confirmed in the 6, 7 and 8th right ribs, the 6 and 7th thoracic vertebrae and in the liver and spleen. The lesions were diagnosed as GSD based on clinical findings, imaging characteristics and needle biopsy results. The patient was treated with zoledronic acid, activated vitamin D, propranolol and radiotherapy to the thoracic vertebrae. However, approximately 5 months after the first treatment, the rapidly increasing hemorrhagic pleural effusion compressed the left lung and caused a mediastinal shift to the right thorax. Unfortunately, the patient succumbed to the disease 7 months after first admission. To the best of our knowledge, this is the first reported case of GSD in the rib and thoracic spine with spinal injury to be treated with radiotherapy, propranolol, vitamin D and zoledronic acid. Furthermore, there have been no previous reports of a mediastinal shift caused by intralesional hemorrhage in GSD. For future reference, it should be noted that such processes may occur in GSD lesions of the thoracic spine and/or thorax. The present case will therefore contribute to a deeper understanding of GSD, a rare clinical entity.

Surgical Management of Gorham-Stout Disease in Cervical Compression Fracture with Cervicothoracic Fusion: Case Report and Review of Literature

BACKGROUND

Gorham-Stout disease (GSD) or "vanishing bone" disease is characterized by progressive osteolysis with intraosseous lymphangiomatosis (hemangiomatosis). Given its rarity, with about 300 reported cases, its pathophysiology, etiology, and treatment guidelines are not established yet.

CASE DESCRIPTION

A 22-year-old man was admitted to Severance Hospital with the chief complaint of neck pain from an injury due to falling. Initial cervical radiography showed a C4 burst fracture, and cervical magnetic resonance imaging revealed diffuse osteolytic lesions with coarse trabeculation with T2 hyperintensity and T1 enhancement in the entire cervical and upper thoracic area. He had a previous history of chylothorax that was still noticeable on a chest radiograph at the time of admission. A 2-stage operation was conducted. First, anterior corpectomy of C4 and anterior plate fixation of C3-5 were performed. Second, a week later, posterior fixation of C3-5 was performed. Thereafter, the patient was discharged without any neurologic complications. However, during the 1-month follow-up, asymptomatic progressive kyphosis was detected via radiography, and posterior cervical fusion of C2-T4 was performed. A minimal postoperative symptom of an intermittent left arm pain of 4-5 on the visual analog scale was experienced. No further deformity progression was noted until the last outpatient follow-up.

CONCLUSIONS

Spinal GSD can cause severe deformity and neurologic deficits such as paralysis. Although treatment for GSD is not established, surgical treatment is recommended in severe deformity or aggravated neurologic deficit. The appropriate timing of surgery is after the arrest of osteolysis. Magnetic resonance imaging could be helpful in determining stable GSD.

Chylous Manifestations and Management of Gorham-Stout Syndrome

Gorham-Stout disease (GSD) was first described by Gorham and colleagues in 1954, but its precise mechanism and cause remain to be elucidated. In this condition, voluminous and potentially fatal chylous effusions into the thorax can occur. Herein, we describe a case of GSD in which the patient presented with massive pleural effusions and mottled osteolytic bone lesions. We performed multiple operations, including thoracic duct ligation using video-assisted thoracoscopic surgery and thoracotomic decortication, but these procedures did not succeed in preventing recurrent pleural effusion and chest wall lymphedema. After administering sirolimus (0.8 mg/m², twice a day) and propranolol (40 mg, twice a day), the process of GSD in this patient has been controlled for more than 2 years.

Successful Management of Gorham-Stout Disease in Scapula and Ribs: A Case Report and Literature Review

Gorham-Stout disease (GSD) is an extremely rare bone condition of unknown etiology characterized by spontaneous and progressive resorption of bones. GSD can occur at any age and is not related to gender, genetic inheritance, or race. Any part of the skeleton can be affected and the symptoms correlate with the sites involved. The diagnosis of GSD is established based on the combination of clinical, radiologic, and histologic features after excluding other diseases. Because of its rarity, current knowledge is limited to case reports and there is no agreement on the best strategy for treatment. The following case report describes a successfully treated case of GSD in a 26-year-old male patient with the left scapula and the 7th-9th left ribs involved. The patient was diagnosed with osteoporosis-related pleural effusion at a local hospital. In our institution, the patient was diagnosed with GSD and treated with radiotherapy and bisphosphonate. The disease was controlled and there was no evidence of disease progression during follow-up. Genetic sequencing was performed to investigate the etiology of GSD. In addition, the present study reviews the theories regarding the etiology, the clinical manifestations, the diagnostic approaches, and treatment options for this rare disease.

Multifocal osteolysis with chylous polyserositis and intrathoracic vein thrombosis: a diagnostic challenge for rheumatologists

Vanishing bone disease with multisystemic involvement may mimic systemic autoimmune or autoinflammatory diseases. We present a 19-year-old man who was hospitalized due to chest pain following a progressive osteolysis of the bony thorax. The disease later expanded into the pleura, peritoneum and pericardium in a form of massive chylous polyserositis. The patient also developed thrombosis of multiple central veins, which in turn worsened the chylothorax by increasing the pressure in the thoracic duct. This is the first case of vanishing bone disease complicated by triple chylous effusions and central vein thrombosis.

Two cases of Gorham-Stout disease with good response to zoledronic acid treatment

Gorham-Stout disease - also called vanishing bone syndrome - is a rare bone disease characterized by a progressive intra-osseous proliferation of non-neoplastic vascular tissue resulting in massive osteolysis. Here, we report two clinical cases of Gorham-Stout disease. Case 1: a 56-year-old woman with 20 years of history of pain and swell in elbows, ankles and wrist. Then she was diagnosed as systemic lupus erythematosus (SLE) with glomerulonephritis type III. After other pathologies were ruled out Gorham-Stout disease was diagnosed. Intravenous zoledronic acid (5 mg) was indicated and after third infusion a progressive improvement of pain, mobility and daily activities were observed. Case 2: a 70-years-old man with a history of pain and limited motion in the left shoulder without X-ray abnormality. Six months later pathological fracture in the left humerus occurred and after ruled out other pathologies Gorham-Stout disease was diagnosed. Intravenous zoledronic acid (5 mg) was indicated and a good response was observed after the first infusion. Nowadays just over 200 cases were reported. Gorham-Stout disease was reported in different bones, at different age presentation and severe physical deformities, disabilities, and life-threatening complications can occur. Two cases of Gorham-Stout disease with good response to zoledronic acid was reported in this article.

From tooth extraction to Gorham-Stout disease: A case report

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Gorham-Stout disease (GSD) is a very rare idiopathic bone disorder characterised by spontaneous and progressive osteolysis, associated with angiomatous proliferation and soft tissue swelling without new bone formation.

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The clinical presentation of GSD includes pain, functional impairment, and swelling, although a few asymptomatic cases have been reported, similar to our case.

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We present this rare case of GSD with several localisations to emphasise that any procedure appearing to be simple can go catastrophically wrong and can result in the discovery of something that is unexpected and extremely rare.

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We wish to emphasise the extreme rarity of the case, focusing on the large difference between the preoperative panoramic radiograph and whole-body CT and MRI images obtained on the day after the first surgical procedure.

Introduction

Gorham-Stout disease (GSD), or vanishing bone disease, is a very rare condition of unknown aetiology. It is characterised by progressive osteolysis and angiomatosis.

Case presentation

We report the discovery of this very rare disease following a trivial deciduous tooth extraction in a 14-year-old female. We focus initially on the difference between the preoperative orthopantomography and the whole-body computed tomography and magnetic resonance images obtained post-haemorrhage, and then on the improvement of strategies for the correct diagnosis and treatment of this disease.

Discussion

Bone loss and the proliferation of vascular structures can occur in a single bone or spread to soft tissue and adjacent bone; areas commonly affected by GSD include the ribs, spine, pelvis, skull, clavicle, and the maxillofacial area. The clinical presentation of GSD includes pain, functional impairment, and swelling, although a few asymptomatic cases have been reported, similar to our case.

Conclusion

We report a very rare case of this multicentric disease in an asymptomatic child who presented for dental extraction, almost died, and was then diagnosed with and treated for GSD.

Pulmonary and pleural lymphatic endothelial cells from pediatric, but not adult, patients with Gorham-Stout disease and generalized lymphatic anomaly, show a high proliferation rate

Background

Gorham-Stout disease (OMIM 123880) and generalized lymphatic anomaly are two rare disorders of lymphendothelial growth in which thoracic involvement with chylothorax is a feared complication. Currently it is believed that both disorders are prenatal malformations that progress slowly after birth. Several pharmaceuticals with antiproliferative properties, including interferon-α-2b, rapamycin and propranolol, have however been shown to affect the disease course in some patients. Deeper knowledge of the growth characteristics of these malformations are therefore needed to guide the clinical approach.

Methods

Lymphatic vessels in lung and pleural tissue from both children and adult patients with generalized lymphatic anomaly or Gorham-Stout disease were studied using an immunohistochemical approach, targeting lymphendothelial markers (D2-40/Prox-1) and a proliferation marker (Ki-67).

Results

We found significant proliferation and growth in these lesions in pediatric patients but not in adults. Furthermore, the data may suggest that the disease process is at least partly reversible.

Conclusions

These malformations of the lymphatic system proliferate at a significant rate long after birth, which could suggest that the clinical approach for children should be different from adults.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0449-4) contains supplementary material, which is available to authorized users.

Clinical Features and Prognosis of Generalized Lymphatic Anomaly, Kaposiform Lymphangiomatosis, and Gorham-Stout Disease

BACKGROUND

Complex lymphatic anomalies are intractable lymphatic disorders, including generalized lymphatic anomaly (GLA), Gorham-Stout disease (GSD), and kaposiform lymphangiomatosis (KLA). The etiology of these diseases remains unknown and diagnosis is confused by their similar clinical findings. This study aimed to clarify the differences in clinical features and prognosis among GLA, KLA, and GSD, in Japanese patients.

PROCEDURE

Clinical features, radiological and pathological findings, treatment, and prognosis of patients were obtained from a questionnaire sent to 39 Japanese hospitals. We divided the patients into three groups according to radiological findings of bone lesions and pathology. Differences in clinical findings and prognosis were analyzed.

RESULTS

Eighty-five patients were registered: 35 GLA, 9 KLA, and 41 GSD. Disease onset was more common in the first two decades of life (69 cases). In GSD, osteolytic lesions were progressive and consecutive. In GLA and KLA, 18 patients had osteolytic lesions that were multifocal and nonprogressive osteolysis. Thoracic symptoms, splenic involvement, and ascites were more frequent in GLA and KLA than in GSD. Hemorrhagic pericardial and pleural effusions were more frequent in KLA than GLA. GSD had a significantly favorable outcome compared with combined GLA and KLA (P = 0.0005). KLA had a significantly poorer outcome than GLA (P = 0.0268).

CONCLUSIONS

This survey revealed the clinical features and prognosis of patients with GLA, KLA, and GSD. Early diagnosis and treatment of KLA are crucial because KLA has high mortality. Further prospective studies to risk-stratify complex lymphatic anomalies and optimize management for KLA are urgently needed.

Increased Intracranial Pressure in a Boy with Gorham-Stout Disease

Gorham-Stout disease (GSD), also known as vanishing bone disease, is a rare disorder, which most commonly presents in children and young adults and is characterized by an excessive proliferation of lymphangiomatous tissue within the bones. This lymphangiomatous proliferation often affects the cranium and, due to the proximate location to the dura surrounding cerebrospinal fluid (CSF) spaces, can result in CSF leaks manifesting as intracranial hypotension with clinical symptoms to include orthostatic headache, nausea, and vertigo. We present the case of a boy with GSD and a known history of migraine headaches who presented with persistent headaches due to increased intracranial pressure. Although migraine had initially been suspected, he was eventually diagnosed with intracranial hypertension after developing ophthalmoplegia and papilledema. We describe the first known instance of successful medical treatment of increased intracranial pressure in a patient with GSD.

Disappearing bone disease of the humerus and the cervico-thoracic spine: a case report with 42-year follow-up

BACKGROUND CONTEXT

Disappearing bone disease (DBD) is a rare idiopathic musculoskeletal disorder that is distinguished by bone resorption without bone formation, vascular or lymphatic vessel proliferation, and soft-tissue swelling. Long-term follow-up of a patient with DBD has rarely been reported in the literature.

PURPOSE

The following is a case report of a female patient with DBD of the humerus and the spine who was followed for 42 years, documenting the progression of the disease and outcomes.

STUDY DESIGN

Case report.

METHODS

A review of the medical records since the time of initial hospital admission throughout follow-up was performed.

RESULTS

A female patient was first seen at our institution at the age of 14. She later developed DBD of the humerus and the spine. The initial difficulty encountered was reaching the diagnosis, and later on with management of the patient as the disease progressed. The case was complicated by syrinx and arachnoid cyst formation, which caused neurologic changes leading to tetraplegia and shunt infection. The patient's inability to form a solid fusion mass led to repeated implant loosening and progressive deformity despite efforts made to stabilize both the humerus and the spine. The treatment modalities used were oral bisphosphonates, rhBMP, repeated surgeries, and instrumentation with adjunct bone graft and substitutes. At the age of 56 years, the patient died because of septicemia secondary to urinary tract infection from tetraplegia.

CONCLUSIONS

To our knowledge, this is the first report documenting a 42-year follow-up of a patient with DBD of the humerus and the spine. Our report showed that DBD greatly affects the quality of life of the patient. Close follow-up, a multidisciplinary approach, and supportive care are stressed when managing patients with DBD.

Cerebrospinal fluid leakage in Gorham-Stout disease due to dura mater involvement after progression of an osteolytic lesion in the thoracic spine

Patients with Gorham-Stout disease (GSD), a rare disease of poorly understood etiopathophysiology, suffer from progressive osteolysis. Destruction of bone matrix is caused by lymphatic vessels, which can lead to CSF leakage if parts of bony structures adjacent to CSF spaces are involved. So far, fewer than 200 patients have been reported in the literature; only 4 of these patients presented with CSF leakage. The authors report the case of a 30-year-old man with GSD and CSF leakage due to dura mater involvement after progression of an osteolytic lesion in the thoracic spine. Neurosurgical intervention, including dura repair, was needed. Experimental medical therapy with rapamycin was started, leading to disease control for more than 12 months. Progression of GSD can lead to destruction of the meninges, causing CSF leakage. The authors review 4 other cases reported in the literature and discuss therapeutic options.

Rare bone diseases and their dental, oral, and craniofacial manifestations

Hereditary diseases affecting the skeleton are heterogeneous in etiology and severity. Though many of these conditions are individually rare, the total number of people affected is great. These disorders often include dental-oral-craniofacial (DOC) manifestations, but the combination of the rarity and lack of in-depth reporting often limit our understanding and ability to diagnose and treat affected individuals. In this review, we focus on dental, oral, and craniofacial manifestations of rare bone diseases. Discussed are defects in 4 key physiologic processes in bone/tooth formation that serve as models for the understanding of other diseases in the skeleton and DOC complex: progenitor cell differentiation (fibrous dysplasia), extracellular matrix production (osteogenesis imperfecta), mineralization (familial tumoral calcinosis/hyperostosis hyperphosphatemia syndrome, hypophosphatemic rickets, and hypophosphatasia), and bone resorption (Gorham-Stout disease). For each condition, we highlight causative mutations (when known), etiopathology in the skeleton and DOC complex, and treatments. By understanding how these 4 foci are subverted to cause disease, we aim to improve the identification of genetic, molecular, and/or biologic causes, diagnoses, and treatment of these and other rare bone conditions that may share underlying mechanisms of disease.