Cunniff C, Jones K L, Jones M C, Saunders B, Shepard T, Benirschke K
Department of Pediatrics, UCSD Medical Center 92103.
Am J Med Genet. 1988 Nov;31(3):669-77. doi: 10.1002/ajmg.1320310323.
We evaluated six pairs of conjoined twins: four pairs were dicephalus, and two were of the ischiopagus type. In three of the four dicephalus pairs, the right twin had an abnormality of laterality that included a right aortic arch, reversed great vessel orientation, bilateral right-sided isomerism of the lungs, asplenia, and situs inversus of the viscera. The left twin had normal great vessel orientation and situs solitus in each case. The finding that was unique in these three dicephalus twin pairs was their fused hearts, which were similar in orientation and configuration. The fourth dicephalus twin pair had one normally rotated heart, which was located in the midline and had normally placed chambers and great vessels. Each twin of this pair had normal visceral situs. In the two pairs of ischiopagus twins, each pair had two separate hearts, with normal cardiac structure and great vessel relationships. The viscera expressed normal laterality. Documentation of a defect in laterality in the right twin in three conjoined twin pairs with fusion of the hearts, combined with the presence of normal laterality in three pairs without cardiac fusion, has implications regarding the mechanisms leading to laterality of the human embryo. We suggest that rotation of the heart initiates the embryo's process of lateralization and that the laterality defects of the viscera seen in the right twin are a result of their abnormal cardiac rotation.
四对为双头联体，两对为坐骨连体类型。在四对双头联体中的三对里，右侧双胞胎存在左右侧异常，包括右位主动脉弓、大血管方向反转、双侧右肺异构、无脾以及内脏反位。在每种情况下，左侧双胞胎的大血管方向正常且内脏位置正常。这三对双头联体双胞胎独特的发现是他们融合的心脏，其方向和形态相似。第四对双头联体双胞胎有一颗正常旋转的心脏，位于中线，腔室和大血管位置正常。这对双胞胎中的每一个内脏位置都正常。在两对坐骨连体双胞胎中，每对都有两颗独立的心脏，心脏结构和大血管关系正常。内脏表现出正常的左右侧性。记录到三对心脏融合的连体双胞胎中右侧双胞胎存在左右侧缺陷，同时三对无心脏融合的双胞胎左右侧正常，这对于人类胚胎左右侧形成机制具有启示意义。我们认为心脏旋转启动了胚胎的左右侧化过程，而右侧双胞胎中所见的内脏左右侧缺陷是其心脏异常旋转的结果。
