In a boy, his mother, and his maternal aunt with Crohn disease (IBD30; 619079), Mao et al. (2018) identified heterozygosity for a C-to-T transition in exon 5 of the CARD8 gene (chr19.48,741,719C-T, GRCh37), resulting in a val44-to-ile (V44I) substitution in the T60 isoform. The mutation, which was not found in the boy's unaffected father, was present in the gnomAD database at a minor allele frequency of 0.0015%. Proband serum showed increased levels of the cytokines IL1B (147720) and IL6 (147620) compared to sex-matched control sera. In addition, supernatants from proband peripheral blood mononuclear cells and monocyte cultures had significantly increased amounts of IL1B compared to controls, consistent with dysregulation of the NLRP3 (606416) inflammasome. Cells from the proband's affected mother and aunt displayed similar overactivity, suggesting that the V44I mutation negates the inhibitory role of CARD8 on NLRP3 inflammasome activation. Experiments with transfected HEK293 cells demonstrated that the V44I mutant exerts a dominant-negative effect by binding to and forming oligomers with unmutated T60 or T48 CARD8, which impedes binding to NLRP3. Additional studies suggested that overactivation of the NLRP3 inflammasome in CD patients with the V44I mutant is caused by both reduced phosphorylation and reduced polyubiquitination of NLRP3.
