Carriers of IKZF1 pathogenic variants exhibit clinical features including immunological dysregulation (e.g., autoimmunity, immunodeficiency) with ~65–70% penetrance and a 10% risk of developing lymphoid malignancies, particularly B-ALL, by age 20 years and less commonly, T-cell acute lymphoblastic leukemia (T-ALL) and non-Hodgkin lymphoma (NHL) [9, 72]. This evidence concerns the gene IKZF1 and T-cell acute lymphoblastic leukemia.