PLCG2 and Familial cold urticaria: The main differential diagnoses of FCAS include isolated acquired cold urticaria, in which family history is negative and no systemic symptoms are observed during the attacks, and the newly described autosomal dominant forms of familial cold urticaria due to alterations in NLRP12 (61), PLCG2 (PLCG2-associated antibody deficiency and immune dysregulation - PLAID syndrome, in which urticaria-like rash is associated to antibody deficiency) (62), and NLRC4 genes (63).