The first case-control study investigating the association between KIR genes and CN found that KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL4, KIR3DL1, KIR3DL2, KIR2DL3, and KIR2DS4 are associated with an increased CN risk, while the KIR2DL5 is protective [157]. This evidence concerns the gene KIR2DL4 and cyclic hematopoiesis.