Congenital condition of the large intestine; constipation is the most important symptom, caused by nerve cells missing in part of the intestinal wall which normally provides peristaltic movement. There can be symptoms shortly after birth, when the baby passes no meconium, or passes it with difficulty; others suffer later from persistent constipation. Because the abnormality usually occurs at the end of the large intestine, faeces accumulate in the preceding section, causing it to distend; the condition is worsened by the accumulation of intestinal gas. Affected children sometimes have a distended, hard abdomen, with peristalsis visible in the healthy section of the intestine. In some cases the condition can lead to ileus (intestinal obstruction), a serious condition requiring immediate treatment. This disorder is always suspected in all cases of abdominal distension and persistent constipation in babies. In contrast to normal constipation, no faeces are found on rectal examination. X-rays show distended intestinal loops above the abnormality. Diagnosis can be confirmed only by microscopic examination of a piece of intestinal mucous membrane removed by biopsy; there is no nerve tissue. Treatment is directed at first at the constipation, using diet, medication and possibly an enema. After a time the abnormal section of the intestine usually has to be removed by surgery, almost always with good results.