SOS1 and Splenomegaly: An analysis of a smaller number of older animals eventually reaching 14 months of age showed that these older SOS1/2-KO mice develop CML-related splenomegaly similar to that shown in young 9-month-old WT mice (Figure S2), suggesting that the SOS2-KO mice eventually develop similar, though later, CML phenotypes than WT mice carrying a normal dosage of SOS proteins.