Autoinflammatory diseases encompass a group of inherited disorders characterized by genetic defects in innate immunity and leading to uncontrolled systemic or organ-specific inflammation. While familial Mediterranean fever is a common example prevalent in Mediterranean regions, autoinflammatory phospholipase C gamma 2 (PLCG2)-associated antibody deficiency and immune dysregulation (APLAID) is extremely rare. We present a 36-year-old male patient with recurrent pustular eruptions who was on colchicine treatment for FMF. Genetic analysis revealed a heterozygous c.2120C > A (Ser707Tyr) mutation in the PLCG2 gene. Daily anakinra 100 mg therapy provided long-term control on skin eruptions. A case-based review following CaBArET guidelines was conducted using Medline/PubMed and Scopus databases and identified 30 cases of APLAID to review the clinical manifestations and treatment approaches of APLAID. No phenotype-genotype association has been established and treatment outcomes of APLAID patients are variable. Our case highlights reconsidering the diagnosis of a patient with persistent and atypical inflammatory manifestations even if he has a diagnosis of an autoinflammatory disorder. Although treatment responses to anakinra reported in the literature are scarce and highly variable, our observations demonstrated that anakinra seems to be a promising agent, especially for recurrent pustular eruptions of APLAID. Key Points • Skin is potentially the most demonstrative and available target of autoinflammatory disorders. • Detailed history, examinations and subsequent WES analysis may provide the correct diagnosis of APLAID, even in a patient who has already an autoinflammatory disorder. • Anakinra may be a promising agent for the treatment of skin eruptions in APLAID patients.

Phospholipase C gamma 2 (PLCG2) gene mutations might cause PLCG2-associated antibody deficiency and immune dysregulation (PLAID)/autoinflammation and PLCG2-associated antibody deficiency and immune dysregulation (APLAID) syndrome. They are two forms of autosomal-dominant immune dysregulation (ID). APLAID patients are usually characterized by skin lesions, pulmonary involvement, and musculoskeletal, ophthalmic, and gastrointestinal tract symptoms, but unlike PLAID patients, these patients do not present with cold urticaria or autoimmunity. Here, we report a 25-year-old man with B-cell lymphopenia, pulmonary bullae, recurrent sinopulmonary infections, and cutis laxa but without cold-induced urticaria. Anti-nuclear antibodies were negative. Trio whole-genome sequencing revealed a de novo heterozygous PLCG2 gene (NM_002661.5) variant c.3417_3419del, p.E1139del, located on chromosome chr16-81973600-81973602. Our findings expand the variety of clinical and genetic phenotypes for APLAID and suggest that this variant would be meaningful.

Phospholipase Cγ2 (PLCγ2) is an important signaling molecule that receives and transmits signals from various cell surface receptors in most hematopoietic lineages. Variants of PLCG2 cause PLCγ2-associated immune dysregulation (PLAID), a family of conditions classified by mutational effect. PLAID with cold urticaria (PLAID-CU) is caused by in-frame deletions of PLCG2 that are dominant negative at physiologic temperatures but become spontaneously active at subphysiologic temperatures. We identified genetic lesions that cause PLAID by combining RNA sequencing of full-length PLCG2 with whole genome sequencing. We studied 9 probands with antibody deficiency and a positive evaporative cooling test, along with 2 known PLAID-CU patients and 3 healthy subjects. Illumina sequencing was performed on full-length PLCG2 cDNA synthesized from peripheral blood mononuclear cell RNA, and whole genome sequencing was used to identify genetic lesions. Novel alternate transcripts were overexpressed in the Plcg2-deficient DT40 cell overexpression system. Extracellular signal-regulated kinase (ERK) phosphorylation was quantified by flow cytometry with and without B-cell receptor crosslinking. Two probands expressed novel alternative transcripts of PLCG2 with in-frame deletions. Proband 1, expressing PLCG2 without exons 18-19, carried a splice site mutation in intron 19. Proband 2, expressing PLCG2 without exons 19-22, carried a 14 kb de novo deletion of PLCG2. DT40 cells overexpressing the exon 18-19 or exon 19-22 deletions failed to phosphorylate ERK in response to B-cell receptor crosslinking. In addition to autosomal dominant genomic deletions, de novo deletions and splice site mutations of PLCG2 can also cause PLAID-CU. All of these can be identified by cDNA-based sequencing.

Phospholipase Cγ2 (PLCγ2) is an important signaling molecule that receives and transmits signals from various cell surface receptors in most hematopoietic lineages. Variants of PLCG2 cause PLCγ2-associated immune dysregulation (PLAID), a family of conditions that are classified by mutational effect. PLAID with cold urticaria (CU-PLAID) is caused by in-frame deletions of PLCG2 that are dominant negative at physiologic temperatures but become spontaneously active at sub-physiologic temperatures. To identify genetic lesions that cause PLAID by combining RNA sequencing of full-length PLCG2 with whole genome sequencing. We studied nine probands with antibody deficiency and a positive evaporative cooling test, together with two known CU-PLAID patients and three healthy subjects. Illumina sequencing was performed on full-length PLCG2 cDNA synthesized from peripheral blood mononuclear cell RNA and whole genome sequencing was used to identify genetic lesions. Novel alternate transcripts were overexpressed in the Plcg2-deficient DT40 cell overexpression system. ERK phosphorylation was quantified by flow cytometry with and without BCR crosslinking. Two probands expressed novel alternative transcripts of PLCG2 with in-frame deletions. The first, expressing PLCG2 without exons 18-19, carried a splice site mutation in intron 19. The second, expressing PLCG2 without exons 19-22, carried a 14kb de novo deletion of PLCG2. DT40 cells overexpressing the exon 18-19 or exon 19-22 deletions failed to phosphorylate ERK in response to BCR crosslinking. In addition to autosomal dominant genomic deletions, de novo deletions and splice site mutations of PLCG2 can also cause CU-PLAID. All of these can be identified by cDNA-based sequencing.

Cherubism is most commonly caused by rare heterozygous gain-of-function (GOF) missense variants in SH3BP2, which appear to signal through phospholipase C gamma 2 (PLCG2) to cause excessive osteoclast activity leading to expansile lesions in facial bones in childhood. GOF variants in PLCG2 lead to autoinflammatory PLCG2-associated antibody deficiency and immune dysregulation (autoinflammatory PLAID, or PLAID-GOF), characterized by variably penetrant autoinflammatory, autoimmune, infectious, and atopic manifestations. Cherubism has not been reported in PLAID to date. We determined whether GOF PLCG2 variants may be associated with cherubism. Clinical, laboratory, and genomic data from 2 patients with cherubism and other clinical symptoms observed in patients with PLCG2 variants were reviewed. Primary B-cell receptor-induced calcium flux was assessed by flow cytometry. Two patients with lesions consistent with cherubism but no SH3BP2 variants were found to have rare PLCG2 variants previously shown to be GOF in vitro, leading to increased primary B-cell receptor-induced calcium flux in one patient's B cells. Variable humoral defects, autoinflammatory rash, and other clinical and laboratory findings consistent with PLAID were observed as well. GOF PLCG2 variants likely represent a novel genetic driver of cherubism and should be assessed in SH3BP2-negative cases. Expansile bony lesions expand the phenotypic landscape of autoinflammatory PLAID, and bone imaging should be considered in PLAID patients.