Furthermore, in OSA patients, SMAD4 mRNA expression was significantly related to expression of BMAL1 (r = 0.3492, p = 0.0272), CLOCK (r = 0.373, p = 0.0164) and NPAS2 (r = 0.4108, p = 0.0085) (Figure 3A–C). Here, SMAD4 is linked to obstructive sleep apnea syndrome.