The Act1-/- phenotype is associated with increased Th17 cells and Th17-related cytokines (IL-17A, IL-21, IL-22), expanded peripheral B cell populations, hypergammaglobulinemia and autoantibody production, as well as splenomegaly, lymphadenopathy, and mild nephritis. The gene discussed is TRAF3IP2; the disease is Splenomegaly.