For example, higher expression of the gene HPCAL4 (Hippocalcin-Like Protein 4) is strongly associated with “worse” SDB phenotypes (higher AHI, lower AvgO2 and MinO2) in monocytes, but this gene has weak associations with SDB phenotypes in T-cells and PBMCs. Here, HPCAL4 is linked to sleep apnea syndrome.