To determine whether the altered HF cycle in DKO mice could be related to changes in molecular clock genes, we examined the expression levels of six CLOCK-regulated genes (Dbp, Npas2, Nr1d1, Per2, Cry2, and Clock) at PD50, when an upregulation of Dbp, Nr1d1, and Per2 normally occurs in WT mouse skin5. This evidence concerns the gene NR1D1 and hydrops fetalis.