TNF and obstructive sleep apnea syndrome: Pertinent to sleep, VDRs and RXRs have been shown to downregulate transcription of RelB gene, a gene encoding a family of transcription factors; collectively referred to as NF-κB [21] that plays a pivotal pro-inflammatory role, both in terms of the production of sleep-regulating substances, such as IL-1 and tumor necrosis factor alpha (TNF-a), but also in terms of the selective activation of inflammatory pathways known to occur in the setting of intermittent hypoxia, as in obstructive sleep apnea (OSA) [22,23].