For example, a SNP in the CLOCK gene (CLOCK.2, aka rs1801260) has been significantly associated with delayed sleep onset, reduced sleep, and insomnia [26], [65], and in our sample, this SNP was part of a multi-locus model that significantly predicted the number of minutes to get out of bed (sleep inertia) specifically for night shift nurses (Table 4). This evidence concerns the gene CLOCK and insomnia.