Severe Autoinflammatory Manifestations and Antibody Deficiency Due to Novel Hypermorphic PLCG2 Mutations

Autoinflammatory diseases (AIDs) were first described as clinical disorders characterized by recurrent episodes of seemingly unprovoked sterile inflammation. In the past few years, the identification of novel AIDs expanded their phenotypes toward more complex clinical pictures associating vasculopathy, autoimmunity, or immunodeficiency. Herein, we describe two unrelated patients suffering since the neonatal period from a complex disease mainly characterized by severe sterile inflammation, recurrent bacterial infections, and marked humoral immunodeficiency. Whole-exome sequencing detected a novel, de novo heterozygous PLCG2 variant in each patient (p.Ala708Pro and p.Leu845_Leu848del). A clear enhanced PLCγ2 activity for both variants was demonstrated by both ex vivo calcium responses of the patient's B cells to IgM stimulation and in vitro assessment of PLC activity. These data supported the autoinflammation and PLCγ2-associated antibody deficiency and immune dysregulation (APLAID) diagnosis in both patients. Immunological evaluation revealed a severe decrease of immunoglobulins and B cells, especially class-switched memory B cells, with normal T and NK cell counts. Analysis of bone marrow of one patient revealed a reduced immature B cell fraction compared with controls. Additional investigations showed that both PLCG2 variants activate the NLRP3-inflammasome through the alternative pathway instead of the canonical pathway. Collectively, the evidences here shown expand APLAID diversity toward more severe phenotypes than previously reported including dominantly inherited agammaglobulinemia, add novel data about its genetic basis, and implicate the alternative NLRP3-inflammasome activation pathway in the basis of sterile inflammation. This work has been partially funded by the following: CERCA Programme/Generalitat de Catalunya (JIA), SAF2015-68472-C2-1-R grant from the Spanish Ministry of Economy and Competitiveness co-financed by European Regional Development Fund (ERDF) (JIA), RTI2018-096824-B-C21 grant from the Spanish Ministry of Science, Innovation and Universities co-financed by ERDF (JIA), AC15/00027 grant from the Instituto de Salud Carlos III/Transnational Research Projects on Rare Diseases (JIA), PI14/00405 grant from the Instituto de Salud Carlos III co-financed by ERDF (RC), PI13/00174 grant from the Spanish Ministry of Economy and Competitiveness co-financed by ERDF (PP), SAF2017-88276-R grant from the Spanish Ministry of Economy, Industry and Competitiveness co-financed by ERDF (PP), ERC-2013-CoG project 614578 from the European Research Council (PP), 20859/PI/18 grant from Fundación Séneca (PP), SAF2015-68472-C2-2-R grant from the Spanish Ministry of Economy and Competitiveness co-financed by ERDF (FC) and RTI2018-096824-B-C22 grant from the Spanish Ministry of Science, Innovation and Universities co-financed by ERDF (FC). MK acknowledges support from CRUK (A16567) and MRC (P028160). H M-B is a Rio Hortega fellowship from Instituto de Salud Carlos III (CM14/00008) and DB acknowledges support from the UCL Impact Studentship.