DNA methylation levels over CpG sites #1, #2, #3, #8, #9, #13, #19, #22, #25 and #28 of the TLR2 promoter region and TLR2 protein expression were all increased in patients with severe OSA as compared with HS, while DNA methylation levels over CpG site #18 of the TLR2 promoter region was decreased (Fig 2 and S2 Table). Here, TLR2 is linked to obstructive sleep apnea syndrome.