This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Clinical Manifestations of GI Disease, Subject name: Pediatrics
A boy comes with complains of vomiting, bloated abdomen and abdominal pain. He has history of attending ice-cream eating competition last night. He also past history of similar episodes following ingestion of milk and milk products. The likely cause : 
Select and explain. 
A. Pancreatic amylase deficiency, B. Lactase deficiency, C. Salivary amylase deficiency, D. Food poisoning
B: Lactase deficiency
Answer: B: Lactase deficiency 
Explanation: Ans. is 'b' Lactase deficiency (Ref. : O.P. Ghai, Pediatrics, 6/e, p 110, 281 (5/e, p. 256), Nelson 17/e, p 1268).History of ice cream ingestion and subsequent symptoms of vomiting, bloated abdomen, are characteristic findings of lactase deficiency.About lactase deficiency.Lactase is a disaccharidase present on intestinal epithelium (brush border)*. It is used to digest lactose (disaccharide).Lactase Deficiency (Symptoms)Symptoms arise after ingestion of food containing lactose (e.g. milk).Symptom - Diarrhoea, vomiting, bloated abdomen.DiagnosisPresence of more than 1/2 percent of reducing substrate in fresh stool.Acidic stools*Abnormal oral sugar tolerance test* (blood glucose rise of less than 20mg/dl above fasting level with a disaccharide load of 2g/kg)Breath H2 excretion of more than 11 ppm*.Enzyme assay on mucosal biopsies showing low levels of disaccharidases.Treatment - low lactose diet.