Melatonin secretion is usually increased during the daytime and decreased at night in
Smith-Magenis syndrome (SMS) and consequently is not a pertinent marker of the circadian phase of the clock in these cases. No data on temperature rhythm is available in SMS, another reliable marker of circadian clock activity. For this reason, we assessed the 24h profiles of core temperature, sleep-wake cycle,
hormones (plasma
cortisol and
melatonin) and plasma and urine 6sulfatoxy-melatonin, the main hepatic
melatonin metabolism in a 31-year-old man diagnosed with a SMS. All circadian rhythms, especially temperature rhythm showed a phase-advance, associated with reverse
melatonin secretion. Plasma and urine 6sulfatoxy-melatonin profiles showed normal
melatonin catabolism and confirmed the reversed
melatonin secretion. Taking in consideration the reverse
melatonin secretion and the phase-advanced temperature rhythm, which is driven by the suprachiasmatic nucleus, we hypothesize that the central clock is more sensitive to afternoon than to morning
melatonin. This different responsiveness to
melatonin according to the time of the day (i.e. chronaesthesia) corroborates the phase response curve of
melatonin secretion to exogenous
melatonin.