SOS1 and chronic myelogenous leukemia, BCR-ABL1 positive: However, we also noticed that the 14-month-old SOS1-KO transgenic mice presented a clearly healthier profile than SOS2-KO mice of the same age with regard to the development of known CML markers, including splenomegaly and the NEU/LYMP ratio (Figure S2), thus confirming the dominant role of SOS1 over SOS2 with regard to CML pathogenesis.