Individual differences in usual sleep times and natural daily rhythms of key clock genes in human white blood cells

Average peak timing for PER3 was 6:05, which is associated with individual sleep-wake timing.

• Circadian oscillations in clock gene expression were more robust for PER3 compared to BMAL1 and PER2.
• Significant correlations were found between individual sleep-wake timing and the phases of melatonin and cortisol.
• PER3 rhythms showed a strong correlation with sleep-wake timing, while PER2 and BMAL1 did not reach significance.
• The correlation between sleep timing and PER3 expression was stronger in individuals with a specific variant of the PER3 gene linked to morningness.
• PER3 expression in leukocytes may serve as a molecular marker for circadian processes that influence sleep-wake timing.

Simplified