Gain-of-function mutations in a member of the Src family kinases cause autoinflammatory bone disease in mice and humans

Abstract

Autoinflammatory syndromes are characterized by dysregulation of the innate immune response with subsequent episodes of acute spontaneous inflammation. Chronic recurrent multifocal osteomyelitis (CRMO) is an autoinflammatory bone disorder that presents with bone pain and localized swelling.Ali18mice, isolated from a mutagenesis screen, exhibit a spontaneous inflammatory paw phenotype that includes sterile osteomyelitis and systemic reduced bone mineral density. To elucidate the molecular basis of the disease, positional cloning of the causative gene forAli18was attempted. Using a candidate gene approach, a missense mutation in the C-terminal region ofFgr, a member of Src family tyrosine kinases (SFKs), was identified. For functional confirmation, additional mutations at the N terminus ofFgrwere introduced inAli18mice by CRISPR/Cas9-mediated genome editing. N-terminal deleterious mutations ofFgrabolished the inflammatory phenotype inAli18mice, but in-frame and missense mutations in the same region continue to exhibit the phenotype. The fact thatFgrnull mutant mice are morphologically normal suggests that the inflammation in this model depends on Fgr products. Furthermore, the levels of C-terminal negative regulatory phosphorylation of FgrAli18are distinctly reduced compared with that of wild-type Fgr. In addition, whole-exome sequencing of 99 CRMO patients including 88 trios (proband and parents) identified 13 patients with heterozygous coding sequence variants inFGR, including two missense mutant proteins that affect kinase activity. Our results strongly indicate that gain-of-function mutations inFgrare involved in sterile osteomyelitis, and thus targeting SFKs using specific inhibitors may allow for efficient treatment of the disease.