The PTPN22 polymorphism is positively associated with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA), formerly known as Wegener’s granulomatosis, but has not been reported in eosinophilic granulomatosis with polyangiitis (eGPA), formerly known as Churg–Strauss syndrome [62,63]. This evidence concerns the gene PTPN22 and eosinophilic granulomatosis with polyangiitis.