To determine the role of specific histone modifying enzymes in the development of OSA and comorbidities, gene expression levels of the KDM1A, KDM4B, KDM4C, KDM5A-D, KDM6B, DOT1L, HDAC1-7, KAT2A, and KAT6B genes, and protein levels of the KDM1A, KDM4, KDM5, KDM6B, and HDAC1-4 were measured in the PBMC samples. This evidence concerns the gene KDM4B and obstructive sleep apnea syndrome.