Twin studies of psychiatric disorders such as schizophrenia and autism spectrum disorder have employed epidemiological approaches that determine heritability by comparing the concordance rate between monozygotic twins (MZs) and dizygotic twins. The basis for these studies is that MZs share 100% of their genetic information. Recently, biological studies based on molecular methods are now being increasingly applied to examine the differences between MZs discordance for psychiatric disorders to unravel their possible causes. Although recent advances in next-generation sequencing have increased the accuracy of this line of research, there has been greater emphasis placed on epigenetic changes versus DNA sequence changes as the probable cause of discordant psychiatric disorders in MZs. Since the epigenetic status differs in each tissue type, in addition to the DNA from the peripheral blood, studies using DNA from nerve cells induced from postmortem brains or induced pluripotent stem cells are being carried out. Although it was originally thought that epigenetic changes occurred as a result of environmental factors, and thus were not transmittable, it is now known that such changes might possibly be transmitted between generations. Therefore, the potential possible effects of intestinal flora inside the body are currently being investigated as a cause of discordance in MZs. As a result, twin studies of psychiatric disorders are greatly contributing to the elucidation of genetic and environmental factors in the etiology of psychiatric conditions.

对精神分裂症和自闭症谱系障碍等精神疾病的双胞胎研究采用了流行病学方法，通过比较同卵双胞胎 (MZ) 和异卵双胞胎之间的一致性率来确定遗传力。这些研究的基础是 MZ 100% 共享其遗传信息。最近，基于分子方法的生物学研究越来越多地应用于检查精神疾病的 MZ 不一致之间的差异，以揭示其可能的原因。尽管新一代测序的最新进展提高了这方面研究的准确性，但人们更加重视表观遗传变化与 DNA 序列变化，因为表观遗传变化是 MZ 中精神疾病不一致的可能原因。由于每种组织类型的表观遗传状态不同，因此除了来自外周血的 DNA 之外，还使用来自死后脑诱导的神经细胞或诱导多能干细胞的 DNA 进行研究。尽管最初认为表观遗传变化是环境因素造成的，因此是不可传播的，但现在知道这种变化可能会在代际之间传播。因此，目前正在研究体内肠道菌群可能产生的潜在影响，作为导致 MZ 不一致的原因。因此，精神疾病的双胞胎研究极大地有助于阐明精神疾病病因中的遗传和环境因素。