Variant in the PLCG2 Gene May Cause a Phenotypic Overlap of APLAID/PLAID: Case Series and Literature Review

Background: Variants in the phospholipase C gamma 2 (PLCG2) gene can cause PLCG2-associated antibody deficiency and immune dysregulation (PLAID)/autoinflammation and PLCG2-associated antibody deficiency and immune dysregulation (APLAID) syndrome. Linking the clinical phenotype with the genotype is relevant in making the final diagnosis. Methods: This is a single center case series of five related patients (4-44 years), with a history of autoinflammation and immune dysregulation. Clinical and laboratory characteristics were recorded and a literature review of APLAID/PLAID was performed. Results: All patients had recurrent fevers, conjunctivitis, lymphadenopathy, headaches, myalgia, abdominal pain, cold-induced urticaria and recurrent airway infections. Hearing loss was detected in two patients. Inflammatory parameters were slightly elevated during flares. Unswitched B-cells were decreased. Naive IgD+CD27- B-cells and unswitched IgD+CD27+ B-cells were decreased; switched IgD-CD27+ B-cells were slightly increased. T-cell function was normal. Genetic testing revealed a heterozygous missense variant (c.77C>T, p.Thr26Met) in the PLCG2 gene in all patients. Genotype and phenotype characteristics were similar to previously published PLAID (cold-induced urticaria) and APLAID (eye inflammation, musculoskeletal complaints, no circulating antibodies) patients. Furthermore, they displayed characteristics for both PLAID and APLAID (recurrent infections, abdominal pain/diarrhea) with normal T-cell function. Conclusion: The heterozygous missense PLCG2 gene variant (c.77C>T, p.Thr26Met) might cause phenotypical overlap of PLAID and APLAID patterns.