Biological Etiology of Major Depressive Disorder ERQ

Etiology

Etiology is a set of causes of a disease or condition. In abnormal psychology, it refers to the factors that contribute to the development of disorders like depression.

Major Depressive Disorder (MDD)

Major Depressive Disorder (MDD) is an affective disorder characterized by changes in mood. According to DSM-5, symptoms include depressed mood, loss of interest/pleasure, significant weight change, insomnia/hypersomnia, psychomotor agitation/retardation, fatigue, feelings of worthlessness/guilt, difficulty concentrating, and suicidal thoughts.

Biological etiology of MDD

Biological explanations for depression focus on genetic factors and neurochemistry (e.g. neurotransmitters like serotonin and hormones like cortisol).

Genetic heritability of depression

Genetic heritability is estimated using twin studies, family studies, adoption studies, and molecular genetics, since it cannot be directly measured.

Falconer model

The Falconer model assumes that phenotype (observed traits) is influenced by genetics, shared environment, and individual environment; used to estimate heritability in twin studies.

Caspi et al. (2003) - Aim

To investigate the interaction between the 5-HTT gene and stressful life events on the risk of developing depression.

Caspi et al. (2003) - Method

Longitudinal study with 847 New Zealand participants; genotyped for the 5-HTT gene (short and long alleles); assessed for life stress and depressive symptoms over time.

Caspi et al. (2003) - Findings

Participants with one or two short alleles of the 5-HTT gene were more likely to develop depression after stressful events, showing a gene-environment interaction.

Caspi et al. (2003) - Conclusion

Genetic factors influence vulnerability to depression, but environmental stress is needed to trigger the disorder.

Caspi et al. (2003) - Strengths

Large sample size; real-world stressors; evidence for gene-environment interaction in depression risk.

Caspi et al. (2003) - Limitations

Self-reported measures may reduce reliability; correlational design cannot prove causation; some complexities of genetics may be oversimplified.

Kendler et al. (2006) - Aim

To estimate the heritability of Major Depressive Disorder (MDD) using a large sample of Swedish twins.

Kendler et al. (2006) - Method

Telephone interviews with 15,493 Swedish twin pairs; diagnosis based on DSM criteria and antidepressant prescription records.

Kendler et al. (2006) - Findings

Heritability of MDD estimated at ~38%, higher in women than men; no significant link to shared environment; unique environmental factors also important.

Kendler et al. (2006) - Conclusion

Supports genetic vulnerability to depression, but highlights importance of non-shared environmental factors.

Kendler et al. (2006) - Strengths

Large, representative sample; twin design reduces environmental confounds; strong statistical power.

Kendler et al. (2006) - Limitations

Cultural specificity to Swedish population; self-report bias; correlational—cannot establish causation.

Holistic Discussion - Genetic vulnerability

Both studies support the idea that genetics contribute to depression, but also emphasize that environmental factors moderate the risk.

Holistic Discussion - Diathesis-Stress Model

Highlights that depression results from an interaction between biological predisposition (diathesis) and environmental stressors.

Holistic Discussion - Need for multi-factorial models

While biological etiology is supported, depression is a complex disorder likely influenced by cognitive and sociocultural factors as well.

Conclusion - Biological etiology of depression

Genetic research supports a biological vulnerability to depression; however, environmental and other psychological factors also contribute, making a comprehensive approach necessary.