Smith and colleagues retrospectively analyzed 250 MDS-del(5q) patients and observed that 16% of these patients had CSNK1A1 mutations, all missense mutations and occurring in a region of this protein highly conserved and involved in ATP catalysis; the presence of CSNK1A1 mutations was associated with reduced response to lenalidomide [47]. The gene discussed is CSNK1A1; the disease is myelodysplastic syndrome.