MDD: Kendler et al (2006)
Kendler et al. (2006) conducted a twin study to determine the role of genetics in major depressive disorder. Twin studies are important in determining genetic inheritance because they compare monozygotic (identical) twins, who share 100% of their genes, with dizygotic (fraternal) twins, who share approximately 50% of their genes. If identical twins show higher concordance rates (both twins developing the disorder)...