Over 70 FOXP3 mutations have been identified in patients with IPEX.[1] Forkhead box protein 3 (FOXP3) has emerged as a key regulator of immune tolerance by virtue of its function as a master switch factor involved in the differentiation of regulatory T (Treg) cells.[2] The typical clinical manifestations of IPEX are early-onset enteropathy, type 1 diabetes mellitus, and skin diseases. Here, FOXP3 is linked to type 1 diabetes mellitus.