Hirschsprung disease (Q46328)

This is a developmental anomaly affecting the intestinal tract characterised by congenital absence of myenteric ganglion cells (aganglionosis) in a segment of the large bowel. Due to the absence of intrinsic innervation of the muscle layers of the affected segment, there is a loss of motor function. This results in an abnormally large or dilated colon (congenital megacolon) with intestinal occlusion or constipation. This condition becomes evident shortly after birth.