The nightly decline in GFR in subjects without severe OSA can be explained by physiological changes syncing with circadian rhythms, such as systemic blood pressure, renal blood flow, regulation of afferent and efferent arteriolar resistance by the renin–angiotensin–aldosterone system, prostaglandin E2, and antidiuretic hormone [12]. This evidence concerns the gene REN and obstructive sleep apnea syndrome.