It has become clear that familial AML with germline CEBPA mutations involves the inheritance of a single copy of mutated CEBPA encoding a granulocyte differentiation factor (261) and that more than 10% of AML with biallelic CEBPA mutations carry a N-terminal frameshift CEBPA germline mutation with acquisition of a C-terminal somatic mutation as a second event in the development of AML (262). The gene discussed is CEBPA; the disease is acute myeloid leukemia.