Genetic Screening of ZNF687 and PFN1 in a Paget's Disease of Bone Cohort Indicates an Important Role for the Nuclear Localization Signal of ZNF687.

Paget's disease of bone (PDB) is a common, late-onset bone disorder, characterized by focal increases of bone turnover that can result in bone lesions. Heterozygous pathogenic variants in the Sequestosome 1 (SQSTM1) gene are found to be the main genetic cause of PDB. More recently, PFN1 and ZNF687 have been identified as causal genes in patients with a severe, early-onset, polyostotic form of PDB, and an increased likelihood to develop giant cell tumors. In our study, we screened the coding regions of PFN1 and ZNF687 in a Belgian PDB cohort (n = 188). In the PFN1 gene, no variants could be identified, supporting the observation that variants in this gene are extremely rare in PDB. However, we identified 3 non-synonymous coding variants in ZNF687. Interestingly, two of these rare variants (p.Pro937His and p.Arg939Cys) were clustering in the nuclear localization signal of the encoded ZNF687 protein, also harboring the p.Pro937Arg variant, a previously reported disease-causing variant. In conclusion, our findings support the involvement of genetic variation in ZNF687 in the pathogenesis of classical PDB, thereby expanding its mutational spectrum.

A Panel-Based Sequencing Analysis of Patients with Paget's Disease of Bone Suggests Enrichment of Rare Genetic Variation in regulators of NF-κB Signaling and Supports the Importance of the 7q33 Locus.

Paget's disease of bone (PDB) is a common bone disorder characterized by focal lesions caused by increased bone turnover. Monogenic forms of PDB and PDB-related phenotypes as well as genome-wide association studies strongly support the involvement of genetic variation in components of the NF-κB signaling pathway in the pathogenesis of PDB. In this study, we performed a panel-based mutation screening of 52 genes. Single variant association testing and a series of gene-based association tests were performed. The former revealed a novel association with NFKBIA and further supports an involvement of variation in NR4A1, VCP, TNFRSF11A, and NUP205. The latter indicated a trend for enrichment of rare genetic variation in GAB2 and PRKCI. Both single variant tests and gene-based tests highlighted two genes, NR4A1 and NUP205. In conclusion, our findings support the involvement of genetic variation in modulators of NF-κB signaling in PDB and confirm the association of previously associated genes with the pathogenesis of PDB.

Genetic Variation in RIN3 in the Belgian Population Supports Its Involvement in the Pathogenesis of Paget's Disease of Bone and Modifies the Age of Onset.

Paget's disease of bone (PDB) is a common, late-onset bone disorder characterized by focal increase of bone turnover. Mutations in the SQSTM1 gene are found in up to 40% of patients and recent GWAS have led to novel associations with several loci. RIN3, the candidate gene located at the associated 14q32 locus, has recently been studied in a British cohort to elucidate its contribution to the pathogenesis. In this study, we performed a genetic screening of RIN3 in an unrelated cohort to validate these findings and to further explore genetic variation in this gene in the context of PDB. In our screening, we examined the 5' untranslated region (UTR), the exonic regions and the intron-exon boundaries of the gene in a control cohort and a patient cohort. Our findings show clustering of variation similar to the British cohort and support a protective role for common genetic variation (rs117068593, p.R279C) in the proline-rich region and a functionally relevant role for rare genetic variation in the domains that mediate binding and activation of its interaction partner, Rab5. Additive regression models, fitted for the common variants, validated the association of the rs117068593 variant with the disease (OR+/+ 0.315; OR+/- 0.562). In addition, our analyses revealed a potentially modifying effect of this variant on the age of onset of the disease. In conclusion, our findings support the involvement of genetic variation in RIN3 in PDB and suggest a role for RIN3 as a potential modifier of the age of onset of the disease.

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.

Resequencing of candidate genes for Keratoconus reveals a role for Ehlers-Danlos Syndrome genes.

The involvement of genetic factors in the pathogenesis of KC has long been recognized but the identification of variants affecting the underlying protein functions has been challenging. In this study, we selected 34 candidate genes for KC based on previous whole-exome sequencing (WES) and the literature, and resequenced them in 745 KC patients and 810 ethnically matched controls from Belgium, France and Italy. Data analysis was performed using the single variant association test as well as gene-based mutation burden and variance components tests. In our study, we detected enrichment of genetic variation across multiple gene-based tests for the genes COL2A1, COL5A1, TNXB, and ZNF469. The top hit in the single variant association test was obtained for a common variant in the COL12A1 gene. These associations were consistently found across independent subpopulations. Interestingly, COL5A1, TNXB, ZNF469 and COL12A1 are all known Ehlers-Danlos Syndrome (EDS) genes. Though the co-occurrence of KC and EDS has been reported previously, this study is the first to demonstrate a consistent role of genetic variants in EDS genes in the etiology of KC. In conclusion, our data show a shared genetic etiology between KC and EDS, and clearly confirm the currently disputed role of ZNF469 in disease susceptibility for KC.

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.

Familial Paget's disease of bone: Long-term follow-up of unaffected relatives with and without Sequestosome 1 mutations.

OBJECTIVE: Familial Paget's disease of bone is inherited as an autosomal-dominant trait and mutations in the sequestosome 1 (SQSTM1) gene have been reported with variable frequency in patients with familial disease. The natural history, however, of the disease in family members with or without SQSTM1 mutations is unknown. METHODS: To address this question, we investigated members of families with Paget's disease identified and genotyped in 2000 in The Netherlands without clinical, biochemical or radiological signs of Paget's disease. Seventy-five subjects, median age 56 years (range 44-93), with or without SQSTM1 mutations participated in the present study. Medical history was obtained and clinical examination and laboratory investigations were performed in all. When serum biochemical markers of bone turnover were increased, skeletal scintigraphy with SPECT-CT was performed. RESULTS: After a mean period of 15.9 ±â€¯0.32 (SD) years no subject without SQSTM1 mutations (either from positive or negative families) developed Paget's disease. Of 14 carriers of SQSTM1 mutations, Paget's disease of the pelvis was diagnosed in a 74-year old asymptomatic woman. CONCLUSION: The incidence of new Paget's disease in SQSTM1 positive subjects was 7.1% and no mutation-negative subject developed the disease within 16 years of follow-up. Subjects without SQSTM1 mutations can be reassured whereas mutation carriers should consider screening. Our findings should be confirmed in other populations as currently unknown environmental factors that might be involved in the development of the disease may differ.