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Transcriptional regulatory gene variations could influence expression patterns and inflammatory propagation in clavicular cortical hyperostosis

Clavicular cortical hyperostosis (CCH) is a rare inflammatory bone disorder of unknown aetiology represented by pain and swelling of the clavicle. Although similar to chronic nonbacetril/recurrent multifocal osteomyelitis (CNO/CRMO), due to lack of recurrence and additional inflammatory sites, it can be considered separate disease in the spectrum. In our previous study microarray gene expression profiling of CCH patients revealed 974 differentially expressed genes involved in various inflammatory processes. Subsequent qRT- PCR in additional number of patients confirmed significantly lower expression of ERBB2 gene and higher expression of TRPM3 and TPRM7 transient receptor potential (TRP) channel genes. Additionally, immunofluorescence microscopy showed high signal of TRPM3 in blood cells of one CCH patient. Based on described findings and other studies which showed TRP channels are involved in inflammasome activation while ERBB activation promotes protective cellular outcomes during inflammation, we hypothesized CCH could be autoinflammatory disease, but the mechanisms responsible for observed expression alterations remained unclear. Objectoive was to identify possible disease causing gene variants in CCH patients using whole exome sequencing (WES). Genomic DNA was extracted from peripheral whole blood samples of three CCH patients. Targeted exome sequencing was performed using the Nextera Rapid Capture Exome Kit (Illumina). The extracted variants were annotated and filtered using the Variant Studio software (Illumina) and Variant Interpreter (Illumina). WES analysis identified 428 shared identical variants among affected individuals. Thirty of these variants were not associated with a gene, 121 were in ZNF717 gene and 277 were distributed in 63 other genes. One heterozygous variant in CTBP2 gene, one in HYDIN gene and six in ZNF717 were classified as likely pathogenic. In this comprehensive study "bottom-up" approach was used in order to elucidate the molecular disease mechanisms of what we believe could be a new disease entity. Previously performed diligent transcriptome analysis and proof-of-concept experiment which confirmed the results on a protein level indicated CCH could be induced by sternoclavicular joint overuse, TRP channel overexpression, inflammasome activation and reduced protection during inflammation. Interestingly, WES analysis identified majority of likely pathogenic variants in ZNF717 gene. This gene encodes a Kruppel-associated box (KRAB) zinc-finger protein, which belongs to a large group of transcriptional regulators and is therefore involved in the regulation of crucial physiological and pathological processes. Many aspects of these proteins are still essentially unknown, as is their role in the inflammation, yet it is speculated they increase DNA accessibility and inflammatory gene transcription. Together with possible influence on observed expression patterns, all of these processes could contribute to CCH evolution.

Clavicular cortical hyperostosis (CCH) ; whole exome sequencing (WES) ; ZNF717 gene

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