In the OSA group, statistically significant associations between evening and morning CLOCK, CRY1, and PER1 gene expressions were found (R = 0.400, p = 0.02; R = 0.468, p = 0.007 and R = 0.528, p < 0.001, respectively), while for BMAL1 only a tendency was present (R = 0.296, p = 0.06). This evidence concerns the gene CLOCK and obstructive sleep apnea syndrome.