In 1999, the autosomal dominant familial platelet disorder with propensity to develop acute myeloid leukemia (now known as RUNX1 Familial Platelet Disorder with Associated Myeloid Malignancies, RUNX1-FPDMM) was the first HHM to have its molecular basis elucidated, driven by heterozygous pathogenic RUNX1 variants (4). The gene discussed is RUNX1; the disease is hereditary thrombocytopenia and hematological cancer predisposition syndrome associated with RUNX1.