Management of Blau syndrome: review and proposal of a treatment algorithm.

Blau syndrome is a rare genetic granulomatosis affecting children. It could be responsible for vision-threatening complications and articular deformation. Due to the rarity of this disease, there are no standardized guidelines for its management. This work aimed to provide an updated overview of the different therapeutic options for Blau syndrome. We conducted research in the PubMed database for the different treatments used in Blau syndrome patients, and we proposed a therapeutic algorithm for disease management. High doses of corticosteroids are considered as a bridging therapy in Blau syndrome. Methotrexate should be initiated if the patient has articular or ocular involvement. An anti-tumor necrosis factor α should be added for patients with uveitis or residual arthritis. If the patient remains symptomatic, a switch to another anti-tumor necrosis factor α is the best option. In non-responders to the first- and second-line biotherapies, a switch to an anti-interleukin 1, an anti-interleukin 6, or tofacitinib is necessary. CONCLUSION: This article suggested an algorithm for the treatment of Blau syndrome. Other studies are necessary to confirm the efficacy of these treatments. WHAT IS KNOWN: • Blau syndrome is a rare but severe granulomatosis that could be responsible for vision-threatening complications and articular deformation. • Blau syndrome seems to be refractory to treatments. WHAT IS NEW: • High doses of corticosteroids are usually insufficient and should be considered only as a bridging therapy. • Blau syndrome could be considered as a poor factor for uveitis, thus, an anti-tumor necrosis factor α should be initiated for patients with uveitis or with residual arthritis.

Proteomic Profiling of Tears in Blau Syndrome Patients in Identification of Potential Disease Biomarkers.

Blau syndrome (BS) is a rare autoinflammatory granulomatosis characterized by granulomatous arthritis, uveitis, and dermatitis. Ocular complications are particularly severe in BS, significantly contributing to morbidity. This study aims to identify potential biomarkers for BS ocular degeneration through proteomic profiling of tear samples from affected patients. Seven subjects from the same family, including four carriers of the BS-associated NOD2 mutation (p.E383K), were recruited alongside healthy controls. Tear samples were collected using Schirmer strips and analyzed via mass spectrometry. A total of 387 proteins were identified, with significant differences in protein expression between BS patients, healthy familial subjects, and healthy controls. Key findings include the overexpression of alpha-2-macroglobulin (A2M) and immunoglobulin heavy constant gamma 4 (IGHG4) in BS patients. Bioinformatic analysis revealed that differentially expressed proteins are involved in acute-phase response, extracellular exosome formation, and protein binding. Notably, neutrophils' azurophilic granule components, as azurocidin (AZU1), myeloperoxidases (MPO), and defensins (DEFA3), were highly expressed in the most severely affected subject, suggesting a potential role of neutrophils in BS ocular severity. These proteins might be promising biomarkers for ocular involvement in BS, facilitating early detection and tailored treatment strategies.

RIPK2 NODs to XIAP and IBD.

The receptor-interacting protein kinases (RIPKs) are key regulators of inflammatory signalling and cell death pathways triggered by innate immune receptors, and RIPKs have emerged as promising therapeutic targets for treatment of immune-related disorders. RIPK2 mediates signalling responses initiated by the bacterial-sensing pattern recognition receptors nucleotide-binding oligomerization domain-containing proteins 1 and 2 (NOD1/2), which play a key role in regulation of intestinal immunity and inflammation. Modification of RIPK2 by non-degradative ubiquitin chains generated by the E3 ubiquitin ligase XIAP and other ligases govern NOD1/2 signalling. Recent advances suggest that the interaction between RIPK2 and XIAP is a druggable protein-protein interaction to modulate NOD1/2-dependent immune responses. Here, we discuss the mechanistic function of RIPK2 in immune signalling, its clinical relevance, and the on-going efforts to target RIPK2 in inflammatory bowel disease and beyond.

Distinct NOD2 mutations reported in three families with Blau syndrome (BS) from a single center in India - Case series and review of literature.

OBJECTIVE: Blau syndrome (BS), considered a rare pediatric autoinflammatory disease, is characterised by a triad of granulomatous arthritis, dermatitis and uveitis. Here we present a tale of three families visited in our outpatient department in the last two years (2020-2022) where more than one member was affected with either skin, ophthalmological and joint involvement with either biopsy-proven granuloma or genetic mutation at NOD2 gene suggesting the diagnosis of BS. CASE SERIES: The first family had three affected members where the mother and her two children had skin changes, polyarthritis and a pathogenic mutation in NOD2 gene (exon 4, c.1000C > T, p.Arg334Trp) suggesting BS. The second family had two affected members where both mother and her son had uveitis, skin changes with NOD2 mutation at exon 4 with c.1147G > A (p Glu 383 Lys) variant. The son also had polyarthritis and his skin biopsy was suggestive of granulomatous inflammation. In the third family with two affected members, we found a mutation in NOD2 on exon 4 (c 1324C > T, p.Lys 442 Phe) which was described as pathogenic with only one report published till date. CONCLUSION: These three cases presented to us within the last two years and led to a diagnosis of BS in three other family members with discrete mutations (commonest to rarest) on the NOD2 gene in the three families.

Molecular diagnostic yield for Blau syndrome in previously diagnosed juvenile idiopathic arthritis with uveitis or cutaneous lesions.

OBJECTIVE: Diagnostic pitfalls often arise in the community because of potentially misleading similarities between juvenile idiopathic arthritis (JIA) and Blau syndrome, an immune-related disorder caused by NOD2 gene mutations. It remains unclear in which population and to which extent next-generation sequencing techniques can aid in diagnosis. METHODS: We evaluated clinical usefulness of targeted next-generation sequencing in previously diagnosed JIA. Participants were required to have symptoms and signs suspected of Blau syndrome, including at least uveitis or cutaneous lesions in addition to arthritis. Targeted sequencing was conducted on NOD2 gene to detect diagnostic variants classified as pathogenic or likely pathogenic for Blau syndrome. We assessed the molecular diagnostic yield and clinical implications on patient care. RESULTS: Between May 1, 2008, and June 1, 2021, sequencing data were accrued from 123 previously diagnosed JIA (median age: 5 years; female: 62.6%). Targeted NOD2 sequencing yielded a positive molecular diagnosis of Blau syndrome in 21.1% (95% CI, 14.9%-29.2%), encompassing six heterozygous missense mutations classified as pathogenic variants. Among those receiving a molecular diagnosis, changes in clinical management and treatment were considered as having occurred in 38.5%. Nine predictors were identified to be associated with a higher diagnostic yield, providing clinical clues to suspect the possibility of Blau syndrome. CONCLUSION: Among some patients with pediatric-onset arthritis complicated with uveitis or cutaneous lesions, reassessing their diagnosis of JIA may be warranted. Targeted NOD2 sequencing established the molecular diagnosis of Blau syndrome in nearly one fifth of these cases and provided clinically relevant information for patient-care decisions.

Anti-TNF treatment corrects IFN-γ-dependent proinflammatory signatures in Blau syndrome patient-derived macrophages.

BACKGROUND: Blau syndrome (BS) is an autoinflammatory disease associated with mutations in nucleotide-binding oligomerization domain 2. Although treatments with anti-TNF agents have been reported to be effective, the underlying molecular mechanisms remain unclear. OBJECTIVE: We aimed to elucidate the mechanisms of autoinflammation in patients with BS and to clarify how anti-TNF treatment controls the disease phenotype at the cellular level in clinical samples. METHODS: Macrophages were differentiated from monocytes of 7 BS patients, and global transcriptional profiles of 5 patients were analyzed with or without IFN-γ stimulation. Macrophages were also generated from BS-specific induced pluripotent stem cells (iPSCs), and their transcriptome was examined for comparison. RESULTS: Aberrant inflammatory responses were observed upon IFN-γ stimulation in macrophages from untreated BS patients, but not in those from patients treated with anti-TNF. iPSC-derived macrophages carrying a disease-associated mutation also showed IFN-γ-dependent accelerated inflammatory responses. Comparisons of peripheral blood- and iPSC-derived macrophages revealed the upregulation of nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) targets in unstimulated macrophages as a common feature. CONCLUSIONS: IFN-γ stimulation is one of the key signals driving aberrant inflammatory responses in BS-associated macrophages. However, long-term treatment with anti-TNF agents ameliorates such abnormalities even in the presence of IFN-γ stimulation. Our data thus suggest that preexposure to TNF or functionally similar cytokines inducing NF-κB-driven proinflammatory signaling during macrophage development is a prerequisite for accelerated inflammatory responses upon IFN-γ stimulation in BS.

Genetic and Clinical Features of Blau Syndrome among Chinese Patients with Uveitis.

PURPOSE: The American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology call for cautious interpretation of variants as causative of a monogenic disorder by stringent standards. We aimed to reclassify the pathogenicity of nucleotide binding oligomerization domain containing 2 (NOD2) variants according to the ACMG guidelines and to characterize clinical features in patients whose ocular disease might actually be explained by Blau syndrome. DESIGN: Genetic analysis and descriptive study. PARTICIPANTS: A total of 1003 unrelated healthy individuals and 3921 sporadic patients who presented with uveitis. METHODS: Whole-exome sequencing was performed on all healthy participants and 551 patients with uveitis, and targeted NOD2 resequencing was performed on the remaining 3370 patients with uveitis. Pathogenicity for Blau syndrome was classified for NOD2 variants identified by sequencing in study participants according to the ACMG guidelines. Clinical manifestations were compared among NOD2 variants of different levels of classification. MAIN OUTCOME MEASURES: Pathogenicity of variants. RESULTS: Eight NOD2 gain-of-function mutations, p.R334W, p.R334Q, p.E383K, p.G481D, p.W490S, p.M513T, p.R587C, and p.N670K, were classified as pathogenic, and 66 patients (1.7%) with uveitis were diagnosed with Blau syndrome due to these mutations. Of 66 with Blau syndrome, anterior uveitis accounted for 39.4%, posterior uveitis for 9.1%, and panuveitis for 51.5%. A proportion of 21.2% of Blau syndrome presented as multifocal choroiditis, 48.5% had papillitis, and 74.2% showed retinal microvasculitis detected by fundus fluorescein angiography. Six NOD2 variants, p.P268S, p.R311W, p.R471C, p.A612T, p.R702W, and p.V955I, were considered nonpathogenic for Blau syndrome and were identified in 96 patients with uveitis. The incidence of bilateral uveitis (86.4%), secondary glaucoma (47.0%), epiretinal membrane (7.6%), choroidal neovascularization (4.6%), retinal atrophy (10.6%), arthritis (69.7%), joint deformity (51.5%), and skin rash (40.9%) was higher in Blau syndrome than in patients with uveitis carrying non-Blau-causing NOD2 variants. Patients with Blau syndrome permanently experienced overall poorer best-corrected visual acuity. Several rare NOD2 mutations, p.I722L (2 cases), p.T476P (1 case), p.T476del (1 case), and p.R439H (1 case), were newly identified. CONCLUSIONS: Pathogenic NOD2 variants for Blau syndrome were limited to those gain-of-function mutations and were associated with a high risk for arthritis, skin rash, permanent visual loss, and ocular complications in patients with uveitis.

Distinguishing Blau Syndrome from Systemic Sarcoidosis.

PURPOSE OF REVIEW: The purpose of this review is to provide a framework to distinguish Blau syndrome/Early Onset Sarcoidosis and Sarcoidosis clinically. We also discuss relevant differences in genetics, pathogenesis, and management of these diseases. RECENT FINDINGS: Blau syndrome and Sarcoidosis share the characteristic histologic finding of noncaseating granulomas as well as some similar clinical characteristics; nevertheless, they are distinct entities with important differences between them. Blau syndrome and Early Onset Sarcoidosis are due to one of numerous possible gain-of-function mutations in NOD2, commonly presenting before age 5 with a triad of skin rash, arthritis, and uveitis. However, as more cases are reported, expanded clinical manifestations have been described. In systemic Sarcoidosis, there are numerous susceptibility genes that have been identified, and disease is thought to result from an environmental exposure in a genetically susceptible host. It most often presents with constitutional symptoms and pulmonary involvement and typically affects adolescents and adults. This paper reviews the similarities and differences between Blau syndrome and Sarcoidosis. We also discuss the importance of distinguishing between them, particularly with regard to prognosis and outcomes.

A young female with early onset arthritis, uveitis, hepatic, and renal granulomas: a clinical tryst with Blau syndrome over 20 years and case-based review.

Blau syndrome is a rare autosomal dominant monogenic auto-inflammatory disorder characterized by triad of granulomatous polyarthritis, dermatitis, and uveitis. However, it may be difficult to recognize this syndrome in the absence of all three characteristic clinical manifestations. A 3-year-old girl presented with early onset symmetric polyarthritis and developed granulomatous uveitis at 13 years of age. However, Blau syndrome was suspected at 21 years of age when she was diagnosed to have disseminated granulomas in liver and kidneys. Diagnosis of Blau syndrome was confirmed by finding a mutation in NOD2 gene (p.Arg334Gln; FP2678). She was initiated on adalimumab therapy and she showed good response to this treatment. We did a literature search to find out all reported cases of Blau syndrome with disseminated granulomatous inflammation and all cases of Blau syndrome that were treated with adalimumab therapy. Seventeen patients with Blau syndrome have been reported to have granulomas at unusual locations (liver; kidneys; lungs; salivary glands; intestine; and lymph nodes). Adalimumab has been reported to be used in 33 patients with Blau syndrome. The indication to initiate adalimumab in large majority of these patients was persistence of uveitis. A possibility of Blau syndrome should be considered in all children presenting with early onset arthritis (especially with the presence of boggy swelling) and granulomatous uveitis. Granulomas in the liver and kidney are uncommon disease manifestations. Adalimumab may be an effective treatment for patients with Blau syndrome who are resistant to other forms of therapy.

Blau syndrome with pulmonary nodule in a child.

Blau syndrome (BS) is a rare monogenic disease caused by mutation of NOD2/CARD15 gene. A case of Blau syndrome in a 4-year-old Chinese boy c.1001G > A(p.R334Q) mutation in the NOD2 genes reported. Imaging revealed a nodule at the tip of the right lung.

Mutual alteration of NOD2-associated Blau syndrome and IFNγR1 deficiency.

Blau syndrome (BS) is an auto-inflammatory granulomatous disease that possibly involves abnormal response to interferon gamma (IFNγ) due to exaggerated nucleotide-binding oligomerization domain containing 2 (NOD2) activity. Mendelian susceptibility to mycobacterial diseases (MSMD) is an infectious granulomatous disease that is caused by impaired production of or response to IFNγ. We report a mother and daughter who are both heterozygous for NOD2c.2264C˃T variant and dominant-negative IFNGR1818del4 mutation. The 17-year-old patient displayed an altered form of BS and milder form of MSMD, whereas the 44-year-old mother was completely asymptomatic. This experiment of nature supports the notion that IFNγ is an important driver of at least some BS manifestations and that elucidation of its involvement in the disease immunopathogenesis may identify novel therapeutic targets.

Blau syndrome: a rare cause of exuberant granulomatous synovitis of the knee.

Blau syndrome (BS) is a rare autosomal dominant familial granulomatous inflammatory disease presenting in early childhood with dermatitis, arthritis and uveitis. Early-onset sarcoidosis represents the sporadic form, and both are characterised by mutations in the CARD15/NOD2 gene on chromosome 16. We describe a 38-year-old man with known BS who presented for orthopaedic review following right-sided patellar dislocation. MRI of the injured knee demonstrated diffuse synovitis and prominent fatty tissue resembling lipoma arborescens with evidence of recent patellar dislocation. Synovectomy was performed and confirmed granulomatous synovitis. Knee imaging findings are described for the first time. Combining distinct morphological bone changes with synovitis which resembles lipoma arborescens and histology which includes sarcoidal-type granulomatous synovitis should lead the radiologist and pathologist to consider the diagnosis of BS.

Pluripotent stem cell models of Blau syndrome reveal an IFN-γ-dependent inflammatory response in macrophages.

BACKGROUND: Blau syndrome, or early-onset sarcoidosis, is a juvenile-onset systemic granulomatosis associated with a mutation in nucleotide-binding oligomerization domain 2 (NOD2). The underlying mechanisms of Blau syndrome leading to autoinflammation are still unclear, and there is currently no effective specific treatment for Blau syndrome. OBJECTIVES: To elucidate the mechanisms of autoinflammation in patients with Blau syndrome, we sought to clarify the relation between disease-associated mutant NOD2 and the inflammatory response in human samples. METHODS: Blau syndrome-specific induced pluripotent stem cell (iPSC) lines were established. The disease-associated NOD2 mutation of iPSCs was corrected by using a CRISPR-Cas9 system to precisely evaluate the in vitro phenotype of iPSC-derived cells. We also introduced the same NOD2 mutation into a control iPSC line. These isogenic iPSCs were then differentiated into monocytic cell lineages, and the statuses of nuclear factor κB pathway and proinflammatory cytokine secretion were investigated. RESULTS: IFN-γ acted as a priming signal through upregulation of NOD2. In iPSC-derived macrophages with mutant NOD2, IFN-γ treatment induced ligand-independent nuclear factor κB activation and proinflammatory cytokine production. RNA sequencing analysis revealed distinct transcriptional profiles of mutant macrophages both before and after IFN-γ treatment. Patient-derived macrophages demonstrated a similar IFN-γ-dependent inflammatory response. CONCLUSIONS: Our data support the significance of ligand-independent autoinflammation in the pathophysiology of Blau syndrome. Our comprehensive isogenic disease-specific iPSC panel provides a useful platform for probing therapeutic and diagnostic clues for the treatment of patients with Blau syndrome.

S100A12 and S100A8/9 proteins are biomarkers of articular disease activity in Blau syndrome.

OBJECTIVE: To identify biomarkers of articular and ocular disease activity in patients with Blau syndrome (BS). METHODS: Multiplex plasma protein arrays were performed in five BS patients and eight normal healthy volunteers (NHVs). Plasma S100A12 and S100A8/9 were subsequently measured by ELISA at baseline and 1-year follow-up in all patients from a prospective multicentre cohort study. CRP was measured using Meso Scale Discovery immunoassay. Active joint counts, standardization uveitis nomenclature for anterior uveitis cells and vitreous haze by Nussenblatt scale were the clinical parameters. RESULTS: Multiplex Luminex arrays identified S100A12 as the most significantly elevated protein in five selected BS vs eight NHVs and this was confirmed by ELISA on additional samples from the same five BS patients. In the patient cohort, S100A12 (n = 39) and S100A8/9 (n = 33) were significantly higher compared with NHVs (n = 44 for S100A12, n = 40 for S100A8/9) (P = 0.0000004 and P = 0.0003, respectively). Positive correlations between active joint counts and S100 levels were significant for S100A12 (P = 0.0008) and S100A8/9 (P = 0.015). CRP levels did not correlate with active joint count. Subgroup analysis showed significant association of S100 proteins with active arthritis (S100A12 P = 0.01, S100A8/9 P = 0.008). Active uveitis was not associated with increased S100 levels. CONCLUSION: S100 proteins are biomarkers of articular disease activity in BS and potential outcome measures in future clinical trials. As secreted neutrophil and macrophage products, S100 proteins may reflect the burden of granulomatous tissue in BS.

Autoinflammatory Disease-Associated Vasculitis/Vasculopathy.

PURPOSE OF REVIEW: Autoinflammatory diseases (AIDs) constitute several disorders that share similar characteristics, clinical features, disease course, and prognosis. They are characterized by the presence of recurrent episodes of unprovoked inflammation due to dysregulated innate immune system in the absence of autoantibodies or infections. AIDs include periodic fever syndromes and other less commonly growing list of syndromes. In this review, vasculitis associated with different AIDs will be highlighted. RECENT FINDINGS: Vasculitis is inflammation and necrosis of the blood vessels causing impaired blood flow, ischemia, and infarction of the dependent tissues. It is a very rare manifestation of AIDs and when it occurs, the skin is the most affected tissue than any other organs such as kidneys, lungs, or CNS. Although vasculitis and AIDs share similar manifestations such as fever, skin rashes, and neuropathy, vasculitis is not a characteristic feature of AIDs and still not clear if it represents a main clinical feature or a manifestation of other disease process.

Familial Blau syndrome without uveitis caused by a novel mutation in the nucleotide-binding oligomerization domain-containing protein 2 gene with good response to infliximab.

The proband in this study was a 4-year-old Mexican girl with Blau syndrome. She and her affected family members had skin rash and arthritis but no uveitis. Exome sequencing and DNA direct sequencing from blood samples revealed a novel nucleotide-binding oligomerization domain-containing protein 2 gene mutation in the affected family members. This study is the first report of a Mexican family with Blau syndrome showing good infliximab treatment response. The novel mutation in the nucleotide-binding oligomerization domain-containing protein 2 gene (c.1808A>G) enriches the mutation spectrum in Blau syndrome. This family represents one of the few cases of autosomal Blau syndrome with no uveitis; because of phenotype variability, it is important to recognize Blau syndrome's clinical spectrum and recommend genetic consultation.

A long-term follow-up of Japanese mother and her daughter with Blau syndrome: Effective treatment of anti-TNF inhibitors and useful diagnostic tool of joint ultrasound examination.

Blau syndrome (BS) is an autosomal dominant autoinflammatory disease associated with NOD2 gene mutations. It is characterized by arthritis, skin rash, and uveitis. Here, we report contrasting outcomes of a daughter and her mother with BS. Their long-term follow-up revealed the efficacy of anti-tumor necrosis factor inhibitor (TNF) with respect to BS. Joint findings of BS feature tenosynovitis over articular synovitis on ultrasonography. BS might be one of the differential diagnoses of juvenile idiopathic arthritis and rheumatoid arthritis.

Successful treatment with adalimumab for severe multifocal choroiditis and panuveitis in presumed (early-onset) ocular sarcoidosis.

Early-onset sarcoidosis (EOS) and Blau syndrome are rare auto-inflammatory diseases characterized by a triad of skin rash, granulomatous uveitis, and symmetrical polyarthritis occurring in early childhood. In this paper, we describe a case report very interesting for the multidisciplinary management (pediatric rheumatologist and ophthalmologist), the challenging diagnosis and the difficult choice of the best treatment. We describe a case report of an 8-year old with recurrent episodes of acute uveitis that developed bilateral granulomatous panuveitis initially treated with topical and systemic steroids. Genetic testing for NOD2/CARD15 revealed a heterozygous mutation on exon 4 in the NBD domain (P268S/SNP5). Therefore, an incomplete EOS was suspected. Because uveitis worsening with multifocal chorioretinitis aggravation, intravenous boluses of methylprednisolone were administered. During the steroids tapering, she flared again, and methotrexate was started along with corticosteroids pulse therapy. However, new ocular granuloma appeared, macular oedema with poor visual outcome occurred, and therefore, adalimumab was added to MTX and steroids. After 6 months since the new therapy started, she had a complete visual recovery, and she was able to stop steroid treatment. At 2 years of follow-up, she is still in remission on treatment, and her visual acuity is normal. No side effects were observed. In our patient, we found a heterozygous mutation on exon 4 in the NBD domain (P268S/SNP5) of NOD2/CARD15 gene and an incomplete EOS was hypothesized. The role of this variant is currently under study. Adalimumab use dramatically changed the course of eye disease, prompting to stop steroid treatment and preserving visual acuity.

Blau syndrome: cross-sectional data from a multicentre study of clinical, radiological and functional outcomes.

OBJECTIVE: To report baseline articular, functional and ocular findings of the first international prospective cohort study of Blau syndrome (BS). METHODS: Three-year, multicentre, observational study on articular, functional (HAQ, Childhood HAQ and VAS global and pain), ophthalmological, therapeutic and radiological data in BS patients. RESULTS: Baseline data on the first 31 recruited patients (12 females and 19 males) from 18 centres in 11 countries are presented. Of the 31 patients, 11 carried the p.R334W NOD2 mutation, 9 the p.R334Q and 11 various other NOD2 missense mutations; 20 patients were sporadic and 11 from five BS pedigrees. Median disease duration was 12.8 years (1.1-57). Arthritis, documented in all but one patient, was oligoarticular in 7, polyarticular in 23. The median active joint count was 21. Functional capacity was normal in 41%, mildly impaired in 31% and moderate-severe in 28% of patients. The most frequently involved joints at presentation were wrists, ankles, knees and PIPs. On radiographs, a symmetrical non-erosive arthropathy was shown. Previously unknown dysplastic bony changes were found in two-thirds of patients. Ocular disease was documented in 25 of 31 patients, with vitreous inflammation in 64% and moderate-severe visual loss in 33%. Expanded manifestations (visceral, vascular) beyond the classic clinical triad were seen in 52%. CONCLUSION: BS is associated with severe ocular and articular morbidity. Visceral involvement is common and may be life-threatening. Bone dysplastic changes may show diagnostic value and suggest a previously unknown role of NOD2 in bone morphogenesis. BS is resistant to current drugs, suggesting the need for novel targeted therapies.