Which statement about irritable bowel syndrome is true?

An underlying neuromuscular or hormonal defect Irritable bowel syndrome, a common cause of alternating diarrhea and constipation, is a functional disorder of motility that probably involves a neuromuscular or hormonal defect. Lactase deficiency is a separate entity that may contribute to irritable bowel syndrome but also may be totally unrelated. There is no evidence of an immunologic defect, and the syndrome is not considered a premalignant state. Incontinence is a symptom of altered anorectal physiology seen with inflammatory diseases of the anal canal and with systemic neuromuscular disorders, such as diabetes or scleroderma; whereas incontinence occasionally may be seen with explosive diarrhea, incontinence is not a common feature of irritable bowel syndrome and should suggest a systemic disorder.