From single cell organisms to the most complex life forms, the 24-hour circadian 
rhythm is important for numerous aspects of physiology and behavior such as 
daily periodic fluctuations in body temperature and sleep-wake cycles. 
Influenced by environmental cues - mainly by light input -, the central 
pacemaker in the thalamic suprachiasmatic nuclei (SCN) controls and regulates 
the internal clock mechanisms which are present in peripheral tissues. In order 
to correlate modifications in the molecular mechanisms of circadian rhythm with 
the pathophysiology of idiopathic hypersomnia, this study aimed to investigate 
the dynamics of the expression of circadian clock genes in dermal fibroblasts of 
idiopathic hypersomniacs (IH) in comparison to those of healthy controls (HC). 
Ten clinically and polysomnographically proven IH patients were recruited from 
the department of sleep medicine of the University Hospital of Muenster. 
Clinical diagnosis was done by two consecutive polysomnographies (PSG) and 
Multiple Sleep Latency Test (MSLT). Fourteen clinical healthy volunteers served 
as control group. Dermal fibroblasts were obtained via punch biopsy and grown in 
cell culture. The expression of circadian clock genes was investigated by 
semiquantitative Reverse Transcriptase-PCR qRT-PCR analysis, confirming 
periodical oscillation of expression of the core circadian clock genes BMAL1, 
PER1/2 and CRY1/2. The amplitude of the rhythmically expressed BMAL1, PER1 and 
PER2 was significantly dampened in dermal fibroblasts of IH compared to HC over 
two circadian periods whereas the overall expression of only the key 
transcriptional factor BMAL1 was significantly reduced in IH. Our study suggests 
for the first time an aberrant dynamics in the circadian clock in IH. These 
findings may serve to better understand some clinical features of the 
pathophysiology in sleep - wake rhythms in IH.