Abstract
Introduction: Individual differences in response to sleep loss have been
described in various settings including driver sleepiness. A potential biological marker for this differential vulnerability is a PERIOD3 (PER3)
Variable Number (4 or 5) Tandem Repeat polymorphism (rs57875989),
for which homozygosity for the 5 repeat (PER35/5) has been associated
with increased homeostatic sleep pressure and cognitive performance
deficits in laboratory conditions. This is the first study so far experimentally investigating the effect of this polymorphism on sleepiness and
performance outside the laboratory.
Methods: 18 PER3 4/4 homozygotes and 10 PER3 5/5 homozygotes
drove during day, evening and night for approximately 90 minutes on
real roads. Subjective sleepiness was measured every 5th minute, physiological sleepiness (blink duration, delay of eyelid reopening) was measured continuously. Driving performance was averaged over the whole
condition.Statistical analyses were conducted using multilevel mixed
effects regression modelling.
Results: Subjective sleepiness showed a steeper rise during evening and
night conditions in PER3 5/5 individuals. The PER3 polymorphism was
also associated with individual differences observed in one of the physiological sleepiness indicators (delay of eyelid reopening). While the
standard deviation of lateral position and blink duration showed clear effects of condition and time on task, PER3 genotype was not significantly
related to individual differences in these measures.
Conclusion: The PER3 VNTR polymorphism contributed significantly
to individual differences in subjective and physiological sleepiness during real road driving; yet observed individual differences were still pronounced.