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Why Monozygotic Twins May Not Share Depression

Summary and Comment |
May 21, 2014

Why Monozygotic Twins May Not Share Depression

  1. Barbara Geller, MD

Heritability is only half the story.

  1. Barbara Geller, MD

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 regions involved in neurodevelopment and function. The most statistically different methylation occurred at an intronic site on a serine/threonine kinase gene. Groups did not differ in life adversities, and the sample was too small to analyze sex differences.

The researchers also examined postmortem DNA samples from the cerebellum of 14 depressed adults and 15 nondepressed adult controls. The same serine/threonine kinase genetic site was identified as significantly different between the two groups.

Comment

This preliminary study highlights an important method of investigating the interplay of genetics and environment in the pathogenesis of depression during adolescence. Future studies can examine sex differences to ascertain if the epigenome is involved in the greater prevalence of depression in girls than boys during the teenage years. Parents with one affected monozygotic child or adults with an affected monozygotic co-twin can be informed that heritability is only half the story and that other genetic changes may help pinpoint which factors lead to alterations of gene function.

Note to readers: At the time NEJM Journal Watch reviewed this paper, its publisher noted that it was not in final form and that subsequent changes might be made.

  • Disclosures for Barbara Geller, MD at time of publication Nothing to disclose

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