CLOCK and cyclic hematopoiesis: The purpose of this study was to evaluate the association between CH and the HCRTR2 (rs10498801, rs2653342,rs2653349, rs3122156, rs3800539, rs9357855), ADH4(rs1126671、rs1800759) and CLOCK (rs1801260) genes, estimating the frequency of different gene haplotypes in a Chinese case–control cohort population.