Clinically, D661 mutations have been detected in both T and NK cell compartments [33, 35, 36] and have been linked to phenotypes such as increased mean corpuscular volume (MCV) [37], altered cytokine profiles and disrupted balance between pro‐ and anti‐inflammatory responses [38, 39, 40]—a reflection of STAT3's central role in regulating immune homeostasis, lymphocyte function and inflammatory signalling, which underlies its contribution to both autoimmunity and tumorigenesis [11, 41]. This evidence concerns the gene STAT3 and Autoimmunity.