Monozygotic (MZ) twin studies constitute a key resource for the dissection of environmental and biological risk factors for human complex disorders. Given that epigenetic differences accumulate throughout the lifespan, the assessment of MZ twin pairs discordant for depression offers a genetically informative design to explore DNA methylation while accounting for the typical confounders of the field, shared by co-twins of a pair. In this review, we systematically evaluate all twin studies published to date assessing DNA methylation in association with depressive phenotypes. However, difficulty to recruit large numbers of MZ twin pairs fails to provide enough sample size to develop genome-wide approaches. Alternatively, region and pathway analysis revealed an enrichment for nervous system related functions; likewise, evidence supports an accumulation of methylation variability in affected subjects when compared to their co-twins. Nevertheless, longitudinal studies incorporating known risk factors for depression such as childhood trauma are required for understanding the role that DNA methylation plays in the etiology of depression.

中文翻译：

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双胞胎研究设计可作为识别抑郁症新候选基因的工具：DNA甲基化研究的系统综述。

单卵双胎（MZ）双胞胎研究是剖析人类复杂疾病的环境和生物危险因素的重要资源。考虑到表观遗传差异在整个生命周期中不断累积，对抑郁症不和谐的MZ双胞胎对的评估提供了遗传学信息设计，以探索DNA甲基化，同时考虑了该领域的典型混杂因素，这是一对双胞胎所共有的。在这篇综述中，我们系统地评估了迄今为止发表的所有双生子研究，这些研究评估了与抑郁表型相关的DNA甲基化。但是，招募大量MZ双胞胎对的困难未能提供足够的样本量来开发全基因组方法。另外，区域和途径分析显示神经系统相关功能丰富。同样 证据表明，与其同卵双胞胎相比，受影响受试者的甲基化变异性不断累积。然而，为了了解DNA甲基化在抑郁症病因中的作用，需要对包括已知的抑郁症危险因素（例如儿童期创伤）进行纵向研究。