This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which of the following condition is associated with Osmotic diarrhoea? 
Select and explain. 
A. Lactase deficiency, B. Ulcerative sprue, C. Surreptitious ingestion of laxatives, D. Endocrine tumors
A: Lactase deficiency
Answer: A: Lactase deficiency 
Explanation: Clinical causes of osmotic diarrhea that causes an osmolar gap greater than 50 includes lactase deficiency, sorbitol foods, saline cathaics and antacids. Osmotic diarrhea occur when water soluble molecules are poorly absorbed, remain in the intestinal lumen and retain water in the intestine. It usually follows ingestion of osmotically active substances. In this, Stool volume is less than 1 litre /day Diarrhea stops with fasting Stool has an osmolar gap (normal stool osmolar gap is less than 50) Ref: Mayo Clinic Internal Medicine Review, Eighth Edition edited by M. Habermann Thomas, page 262.