Schematic representation of our current knowledge of genotype/phenotype relationships in MDS, MDS/MPN, and a related MPN like CNL. The SF3B1 mutation is strictly associated with RARS, whereas the combination of the SF3B1 mutation with subclonal driver mutations in JAK2 or MPL is associated with RARS-T. Thus far, no conclusive genotype/phenotype relationship has been defined within refractory cytopenia with unilineage dysplasia. Various combinations of founding and subclonal driver mutations can be found in RCMD and RAEB. CMML has a relatively well-defined molecular basis, involving primarily somatic mutations of TET2 and SRSF2: comutation of these genes is almost invariably associated with CMML, whereas the ASXL1 mutation involves poor outcome. Within MDS/MPN, aCML is characterized by various founding mutations plus a subclonal mutation of SETBP1. Activating mutations of CSF3R are strictly associated with CNL.