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The twin birth rate has risen recently to 3/100, according to the CDC, and heritability of depression in monozygotic twins is estimated at 48% to 75% (Arch Gen Psychiatry 1996; 53:129). These two statistics warrant examining factors leading to discordance in depression incidence in teenaged monozygotic twins. Researchers conducted a two-part genetic study.
The investigators analyzed buccal DNA from 18 white monozygotic twin pairs (age range, 12–19; 13 female pairs) participating in a larger sibling study; twins were discordant for self-reported major depressive symptoms. Although the genomes of the depressed and nondepressed groups had similar overall methylation rates, they showed differential methylation at multiple sites, most commonly in…