Conversely, variants encoding a STAT3 GOF allele cause an early-onset and heterogeneous multisystemic disease—STAT3 GOF Syndrome—most commonly characterized by polyclonal lymphoproliferation, autoimmunity (cytopenias, enteropathy, endocrinopathies e.g. type 1 diabetes mellitus), infectious disease susceptibility (bacterial, viral, and fungal), skin disease (atopic dermatitis), interstitial lung disease, and growth failure [17]. The gene discussed is STAT3; the disease is type 1 diabetes mellitus.