OP0174 Exome sequencing identifies a hypermorphic missense mutation in the PLCG2 gene as the cause of a dominantly inherited autoinflammatory disease with immunodeficiency

Background Autoinflammatory diseases are inherited disorders of the innate immune system caused by aberrant activation of the innate immune cells, primarily neutrophils and macrophages. Genetic studies have led to the identification of mutations in 12 genes responsible for various monogenic autoinflammatory diseases, however a significant number of mutation negative patients are sporadic cases or come from small families underpowered for linkage analysis. Objectives To identify disease causing mutation in a family with dominantly inherited inflammatory disease characterized by recurrent blistering skin lesions, pulmonary disease, arthralgia, inflammatory eye, bowel disease, absence of autoantibodies, and mild immunodeficiency manifested by recurrent sino-pulmonary infections. Methods Whole-exome sequencing was performed on three samples, including the affected father and daughter and unaffected mother. Exome data were filtered in more than 6000 exomes to exclude reported variants along with benign variants as determined by PolyPhen-2. A total of eight transcripts were identified as possible candidate genes. Results We confirmed a novel variant, p. S707Y, within the PLCG2 gene as the only de novo variant that was present in two affected and not present in four unaffected family members. PLCG2 encodes phospholipase Cγ2 (PLCγ2), an enzyme with a critical regulatory role in various immune and inflammatory pathways. The S707Y mutation is located in an autoinhibitory SH2 domain that is crucial for PLCγ2 activation. In vitro overexpression of the mutant S707Y protein and ex vivo experiments using patients’ leucocytes showed clearly enhanced PLCγ2 activity suggesting an increased intracellular signaling in the PLCγ2-mediated signaling pathway. Our finding that p. S707Y is hypermorphic mutation in PLCγ2 is further corroborated by animal studies that have implicated the critical role for PLCg2 in regulation of inflammation in mice. Two missense gain-of-function mutations in the murine phospholipase Cg2 (Plcg2) gene introduced by ENU mutagenesis, ALI5 and ALI14, lead to severe spontaneous inflammation and autoimmunity. Conclusions Recently, PLCG2 exon skipping mutations were reported in PLAID patients who present with cold-induced urticaria and immune dysregulation resulting in protein products with constitutive phospholipase activity but with reduced intracellular signaling at physiological temperature (ref). In contrast, we report here a missense PLCG2 mutation as