Modeling Strengthens Molecular Link between Circadian Polymorphisms and Major Mood Disorders

Area of Science:

• Genetics
• Chronobiology
• Psychiatry

Background:

• Mood disorders, including major depressive disorder (MDD) and seasonal affective disorder (SAD), affect a significant portion of the global population, with young adults being disproportionately impacted.
• Sleep disturbances and circadian rhythm problems are common in individuals with mood disorders, and genetic studies increasingly support a link between circadian and sleep syndromes and depression/anxiety.
• Mathematical modeling is a critical tool for understanding the mammalian circadian clock's molecular mechanisms and its influence on mood regulation.

Purpose of the Study:

• To model the impact of five clock gene polymorphisms on circadian gene expression, clock period length, and amplitude.
• To investigate the association between these clock gene variants and circadian phenotypes (diurnal preference), depression, and anxiety in a young adult population.

Main Methods:

• Developed a mathematical model to simulate the effects of clock gene polymorphisms on circadian rhythm parameters.
• Assessed circadian phenotypes using the Horne-Ostberg Morningness-Eveningness scores.
• Measured depression and anxiety levels using the Beck Depression Inventory and State-Trait Anxiety Inventory, respectively.
• Analyzed genetic associations in a sample of 546 undergraduates.

Main Results:

• Identified significant associations between CRY2 and two PER3 variants with diurnal preference.
• Found a significant association between a PER3 length polymorphism (rs57875989) and depression.
• Observed that individuals homozygous for a PER3 single nucleotide polymorphism (SNP) (rs228697) reported higher anxiety levels.
• The developed model accurately reflected experimental data and existing knowledge on clock gene polymorphisms and mood.

Conclusions:

• Specific clock gene variants, particularly in PER3, are associated with diurnal preference, depression, and anxiety in young adults.
• The study's mathematical model provides insights into how clock gene mutations affect circadian phenotypes and mood.
• The findings suggest that certain intronic SNPs may act as gain-of-function mutations, increasing transcription rates and potentially contributing to mood disorders.