Investigating Irritability as a Potentially Causal Risk Pathway to Depression Using Two Genetically Informed Designs

Area of Science:

• Psychiatry
• Genetics
• Epidemiology

Background:

• Major depressive disorder (MDD) is a heterogeneous condition with various risk pathways.
• Identifying causal routes to depression is crucial for effective intervention and prevention.
• Irritability is associated with depression risk, but potential confounding factors, including genetics, require investigation.

Purpose of the Study:

• To investigate the causal link between irritability and major depressive disorder (MDD).
• To explore irritability as a potential risk pathway for depression.
• To inform strategies for MDD prevention and early intervention.

Main Methods:

• Utilized the monozygotic twin differences design in the Child and Adolescent Twin Study in Sweden (CATSS) to control for genetic influences.
• Assessed irritability at age 15 and major depressive disorder (MDD) diagnoses from ages 15 to 25 using Swedish National Patient Register (NPR) data.
• Conducted bidirectional two-sample Mendelian randomization (MR) using genome-wide association studies to examine genetic liability for irritability and depression.

Main Results:

• Associations were found between self-reported irritability at age 15 and later MDD diagnoses.
• Monzygotic twin analysis indicated a link between self-reported irritability differences and MDD discordance.
• Mendelian randomization revealed a bidirectional relationship between irritability and depression genetic liability.

Conclusions:

• Self-reported irritability may represent a causal risk pathway to major depressive disorder (MDD).
• Findings suggest irritability could be a viable target for MDD prevention and early intervention.
• Further research can leverage these insights for developing targeted mental health strategies.