Kendler et al (2006)

• Aim:

  To investigate genetic factors influencing Major Depressive Disorder prevalence using a large-scale twin study.
• Research Method:

  Quantitative genetic analysis using twin study methodology.
• Procedure:

  1. The study utilized a large sample of over 40,000 twins from the Swedish twin registry.
  2. The researchers analyzed concordance rates for Major Depressive Disorder (MDD) in monozygotic (identical) and dizygotic (fraternal) twins.
  3. The study compared the concordance rates between monozygotic and dizygotic twins to estimate the genetic contribution to MDD.
  4. The researchers examined differences in concordance rates between males and females.
  5. Using quantitative genetic analysis, they estimated the overall heritability of depression
• Results:

  • Monozygotic twins showed higher concordance rates for MDD than dizygotic twins
  • Females demonstrated higher concordance rates than males
  • Overall heritability of depression was estimated at 38%
  • Higher heritability of MDD was found in women compared to men
• Conclusion:

  The study concluded that there is a significant genetic component to MDD, with genetics playing a larger role in women. This helps explain the consistently observed higher prevalence of MDD in females across populations.
• Strengths:

  1. Large sample size: Over 40,000 twins, enhancing reliability and generalizability of findings
  2. Twin methodology: Allows for robust estimation of genetic and environmental contributions to MDD prevalence
  3. Consistency with previous observations: Findings align with higher prevalence of MDD in females across populations
• Limitations:

  1. Lack of specific gene identification: While demonstrating genetic influence, the study doesn't identify specific genes associated with MDD
  2. Potential overestimation of genetic influence: Twin study method may not fully account for shared environmental factors
  3. Cultural specificity: Conducted in Sweden, potentially limiting generalizability to other ethnicities or cultures
  4. Complexity of MDD: The study highlights genetic factors but doesn't fully explain the complex interplay between genetics and environment in MDD development