CDK5 and obstructive sleep apnea syndrome: Compared with AD-OSA-M group, AD-OSA-MS group had a higher body mass index, lower scores of AVLT N7 and SCWT-C, longer SCWT-C time, higher levels of phosphorylated tau (P-tau) 396 and synaptophysin, lower CDK5 level and smaller volumes of brain gray and white matters in parts of frontal, parietal, temporal and occipital lobes.