Hirschsprung’s disease (HD) is a congenital disorder that is caused by a loss of nerve cells at the end of the bowel. This loss in innervation causes stool to move really slowly or not at all in the parts of the bowel affected. Hence, there is a functional bowel obstruction that arises.
HD typically affects the rectum and sigmoid colon, but it may affect the entire larger intestine and, in rare cases, extend to the first part of the distal small intestine. These clinical presentations allow for HD to be categorized into short-segment HD affecting only the last part of the large intestine or long-segment HD that affects the entire large intestine and part of the small.
The disease is believed to be caused by a failure of nerve cells derived from the neural crest to continue their migration toward the end of the bowel during embryonic development. Normally, neuroblasts (i.e. immature nerve cells) may be identified in the esophagus around the fifth week of pregnancy and are seen in the seventh and later in the eleventh week in the small intestine and colon, respectively. In HD, it is believed that these cells do not complete their journey, leading to that segment of the bowel having no ganglia.
An alternative etiology to the arrested neuroblasts migration is that they may have completed their journey through the entire bowel, but later undergo apoptosis (i.e., cell death) or dysfunctional proliferation and/ or differentiation within the distal bowel. The absence of factors, such as neural cell adhesion molecule (NCAM), laminin, fibronectin and other neurotrophic factors, which are all necessary for the development of enteric ganglia, may have an imperative role in the etiology of HD.
The aganglionosis seen in HD may be the result of mutations in several genes, such as the RET, EDN3 and EDNRB genes. RET gene mutations are believed to be the most common genetic causes of HD. RET plays a crucial role in providing instructions for producing proteins that are necessary for cell signaling and are essential for the normal development of neuroblasts. The EDNRB and EDN3 genes are also involved in coding for proteins that play vital roles that are critical for important cellular processes in the normal formation of the enteric nerve cells. Notwithstanding what is known about these three genes, the genetics of HD is rather complex and still not fully understood.
The signs and symptoms of HD may vary with disease severity and while most often are apparent shortly after the birth of the baby, sometimes they may not appear until later on in the patient’s life. Failure of a newborn to pass stool within the first 24 – 48 hours after birth is the most obviously a typical sign of HD. Furthermore, these newborns may present with brown or green vomit, abdominal swelling, and an explosion of stools after a finger is inserted into the neonate’s rectum.
In toddlers and older children, the signs and symptoms of HD may differ slightly. These patients may not be able to pass stools without the administration of a suppository or an enema. The latter involves using a means to flush fluid into the child’s anus, whereas a pill is deposited into the child’s rectum with the former. In addition to difficulties going to the toilet, these patients may experience slow growth, abdominal swelling and may have diarrhea tinged with blood.