STAT3 and polyendocrinopathy: Other IEIs affect the function of regulatory T (Treg) cells—so-called ‘Tregopathies'—such as immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, deficiencies of CD25 or BTB domain and CNC homolog 2 (BACH2), and gain-of-function mutations in signal transducer and activator of transcription 3 (STAT3) (18).