Attenuated PER3 amplitude in hair follicles is associated with sleep irregularity in schizophrenia

Circadian dysregulation is prevalent in both schizophrenia and obesity, yet the molecular mechanisms underpinning these disturbances remain unclear. We examined circadian variation in clock gene expression using repeated hair follicle self-sampling across two days in 66 adults: 22 with schizophrenia and obesity (SCH-OB), 22 with obesity but no psychiatric disorder (OB), and 22 normal-weight controls (LEAN). Gene expression was quantified by qPCR, and complementary markers included salivary cortisol and melatonin, oral pH and temperature, and accelerometer-derived sleep metrics. Evidence of rhythmic expression was detected in five of six clock genes. PER3 amplitude was significantly reduced in SCH-OB compared with both OB and LEAN (p < 0.01) and correlated positively with sleep regularity (p = 0.006). Cortisol rhythms were preserved across groups, whereas melatonin amplitude was attenuated in SCH-OB relative to LEAN (p < 0.05). Hair follicle sampling proved highly feasible, with >98% compliance. These findings indicate that individuals with schizophrenia exhibit dampened circadian rhythms in PER3 expression that parallel irregular sleep patterns, supporting hair follicle-based sampling as a practical tool for assessing molecular rhythm parameters in real-world conditions.