Circadian rhythms of melatonin and peripheral clock gene expression in idiopathic REM sleep behavior disorder.

OBJECTIVE:To evaluate changes in the expression of clock genes and melatonin levels in patients with idiopathic REM sleep behavior disorder (RBD) as a potential early stage of synucleinopathies. METHODS:We assessed the rhythmicity of circadian clock genes using real time-quantitative polymerase chain reaction and 24-h blood melatonin profiles using radio-immunoassay in 10 RBD patients and nine age-matched controls. RESULTS:The RBD patients did not show circadian rhythmicity for clock genes Per2, Bmal1, and Nr1d1 but the rhythmicity of Per 1 remained, and the amplitude of Per3 was diminished. The 24-h melatonin rhythm did not differ between RBD patients and healthy control subjects. Melatonin profile in RBD patients was delayed by 2 h compared to controls, the habitual sleep phases were phase delayed by about 1 h, however no phase shift occurred in any of the clock genes studied. The control group had stable acrophases of melatonin rhythms of approximately 5 h whereas the RBD patients had a more dispersed range over 11 h. CONCLUSIONS:Our results suggest that RBD could be associated with altered expression of clock genes and delayed melatonin secretion. Thus, we argue that circadian system dysregulation could play a role in RBD.