The increased gene expression of CXCR4 in CD34+ cells and a trend towards increase in mRNA expression for related genes that control homing-in property of endothelial progenitor cells such as VEGFA and NOS3 support the hypothesis that CPAP can improve the functionality of CD34+ cells but the severity of the sleep apnea should be considered. The gene discussed is CXCR4; the disease is sleep apnea syndrome.