These shreds of evidence indicate that the CNS 5-HT plays an important role in REM sleep and cardiorespiratory control, that infants who are deficient in central 5-HT may be at increased risk for SIDS in REM sleep because of increased apnea and delayed arousal, and that cigarette smoking during pregnancy increases the risk of SIDS also. The gene discussed is HTR5A; the disease is sudden infant death syndrome.