What is the primary cause of Hirschsprung disease?

Hirschsprung disease, also known as congenital megacolon, is primarily caused by the congenital absence of ganglion cells, specifically the absence of enteric ganglia in the distal bowel. This absence leads to the failure of the affected segment of the intestine to properly relax and contract, resulting in an obstruction. The condition typically affects the rectum and extends proximally over various lengths into the colon, causing a lack of peristalsis in that segment. As a consequence, stool builds up behind the affected region, leading to abdominal distension and other complications.

Understanding that Hirschsprung disease is fundamentally a developmental disorder related to neural crest cell migration helps clarify why the absence of ganglion cells is the primary issue. This condition is not caused by infections, malrotations, or allergic reactions; thus, the other choices do not correlate with the etiology of Hirschsprung disease.