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American Journal of Medical Genetics Part C (Seminars in Medical Genetics) 148C:180– 185 (2008)

A R T I C L E

The Embryology of Body Wall Closure: Relevance to Gastroschisis and Other Ventral Body Wall Defects
T.W. SADLER* AND MARCIA L. FELDKAMP
During the 3rd and 4th weeks post-fertilization (5 and 6 weeks from the last normal menstrual period [LNMP]), the human embryo is transformedfrom a flat disc-shaped organism into the classic shape of an embryo in the ‘‘fetal’’ position. This change is effected by simultaneously rolling the top layer of the disc, the ectoderm, into the neural tube and the bottom layers of the disc, the endoderm and mesoderm, into the gut tube and body wall, respectively. In this manner, the flat disc is transformed into two tubes, one dorsal to the other,surrounded by supporting structures in the body wall. If closure of the neural tube fails, then neural tube defects (NTDs), such as anencephaly and spina bifida, occur; if closure of the ventral body wall fails, then ventral body wall defects, such as ectopia cordis, gastroschisis, and bladder and cloacal exstrophy, occur. Interestingly, no known closure defects have been described for the gut tube.Note, however, that all of the closure defects that do occur have their origins early in gestation during the third and fourth weeks of development. ß 2008 Wiley-Liss, Inc. KEY WORDS: body folds; body wall; ventral body wall defects; gastroschisis; ectopia cordis; bladder exstrophy; cloacal exstrophy

How to cite this article: Sadler TW, Feldkamp ML. 2008. The embryology of body wall closure:Relevance to gastroschisis and other ventral body wall defects. Am J Med Genet Part C Semin Med Genet 148C:180–185.

EMBRYOLOGY OF BODY WALL DEVELOPMENT
Late in the third week of gestation, the embryo has the shape of an elongated disc and the disc has three germ layers in its cranial half: ectoderm, dorsally; mesoderm in the middle; and endoderm, ventrally. Also, at this stage the embryonicendoderm layer is continuous with the endoderm of the visceral yolk sac; while the embryonic ectoderm is continuous with ectoderm over the amniotic cavity. Thus, the disc is positioned between the amniotic cavity dorsally and the yolk sac cavity ventrally (Figs. 1A and 2A).

Neural tube development (neurulation) is initiated when the central (axial) portion of the ectoderm layer is induced to formthe neural plate whose lateral edges then elevate to form the neural folds [Colas and Schoenwolf, 2001]. These folds consist of neurectoderm and underlying mesenchyme as they continue to elevate and bend toward the midline where they will fuse dorsally at the end of the fourth week to form the neural tube (Fig. 2). The closure process begins in the cranial region and progresses caudally [Sadler,1998; Schoenwolf and Smith, 2000; O’Rahilly and Muller, 2002]. At the same time that neurulation is proceed-

At the same time that neurulation is proceeding, changes occurring in the mesoderm layer portend formation of the body folds and body cavity.
ing, changes occurring in the mesoderm layer portend formation of the body folds and body cavity. This mesodermal layer becomes organized intothree parts: (1) Paraxial mesoderm, that lies along the neural tube and forms segments called somitomeres and somites and that ultimately contributes to formation of the skull, vertebrae, ribs, skeletal muscle, and dermis for skin covering the back; (2) Intermediate mesoderm, lying lateral to paraxial mesoderm, that contributes to development of the urogenital system; (3) Lateral plate mesoderm thatsplits to create the body cavity and forms the smooth muscle of the gut, visceral and parietal serous membranes over the surfaces of the heart, lungs, gut tube

Dr. Sadler is the author of Langman’s Medical Embryology and Langman’s Essential Medical Embryology textbooks. He spent 21 years at the University of North Carolina where he taught Medical Embryology and Anatomy and conducted research...