Lactose intolerance is due to –
**Core Concept**
Lactose intolerance is a condition characterized by the inability to digest lactose, a disaccharide sugar found in milk, due to a deficiency in lactase, the enzyme responsible for its hydrolysis. This deficiency leads to an accumulation of lactose in the small intestine, causing symptoms such as bloating, gas, and diarrhea.
**Why the Correct Answer is Right**
Lactose intolerance is primarily caused by a deficiency in lactase enzyme in the small intestine. Lactase is a β-galactosidase enzyme that breaks down lactose into glucose and galactose, which are then absorbed by the body. A deficiency in lactase enzyme leads to undigested lactose in the small intestine, where it is fermented by colonic bacteria, producing gas and causing symptoms. This is a common condition in many parts of the world, particularly in people of African, Asian, or Native American descent.
**Why Each Wrong Option is Incorrect**
**Option A:** Lactose intolerance is not caused by a deficiency in sucrase, an enzyme that breaks down sucrose into glucose and fructose. While sucrase and lactase are both disaccharidases, they have different specificities and are not directly related to lactose intolerance.
**Option B:** Lactose intolerance is not caused by a deficiency in pancreatic amylase, an enzyme that breaks down starch into oligosaccharides. While pancreatic amylase is involved in carbohydrate digestion, it does not play a role in lactose hydrolysis.
**Option C:** Lactose intolerance is not caused by a deficiency in fructose absorption, which is a separate issue altogether. Fructose malabsorption is a different condition that can cause symptoms similar to lactose intolerance, but it is not the same thing.
**Clinical Pearl / High-Yield Fact**
One key point to remember is that lactose intolerance is not an allergy, but rather a deficiency in an enzyme. This is an important distinction, as it means that people with lactose intolerance can still tolerate small amounts of lactose without experiencing symptoms.
**Correct Answer:** C.