Lactose intolerance is caused by the deficiency of the enzyme:

Appeared in: NVS- 2025

Explanation

Lactose intolerance results from the body's inability to digest lactose, the primary sugar in milk and dairy products.
This inability is due to a deficiency of the enzyme lactase, which is located on the brush border of the small intestine.
Biochemically, lactase is classified as a beta-galactosidase, as it hydrolyzes the beta-glycosidic bond in lactose.
The breakdown of lactose by beta-galactosidase yields two simpler sugars, glucose and galactose, which can then be absorbed into the bloodstream.

Option B: Maltase is the enzyme responsible for breaking down maltose (a sugar found in grains) into two glucose molecules.
Option C: Glucoamylase is an enzyme that aids in the digestion of starch by breaking it down into glucose.
Option D: Sucrase is the enzyme that breaks down sucrose (table sugar) into glucose and fructose.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Biochemistry of carbohydrate digestion and related enzyme deficiencies as background academic context rather than a clinical decision trigger.
Nurses play a key role in educating patients with lactose intolerance about dietary modifications, including reading food labels for 'hidden' lactose in processed foods.
It is crucial to advise patients on alternative sources of calcium and vitamin D (e.g., fortified plant-based milks, leafy greens, supplements) to prevent long-term complications like osteoporosis.
What if? If a patient develops diarrhea and bloating after a bout of viral gastroenteritis, the nurse should recognize this could be temporary (secondary) lactase deficiency. The advice would be to temporarily limit dairy until the gut lining heals, rather than diagnosing a permanent intolerance.

How to Approach the Question

First, identify the key term in the question stem: 'Lactose intolerance'.
Recall the basic physiology of digestion: lactose is the substrate (the substance being acted upon).
Access your knowledge of digestive enzymes. The enzyme that digests lactose is named lactase.
Examine the options. 'Lactase' is not listed directly.
Recognize that questions may use biochemical names. Recall or deduce that lactase is a type of beta-galactosidase, which is the enzyme that hydrolyzes beta-galactoside bonds like the one in lactose.
Eliminate the other options by recalling their functions: Maltase digests maltose, Glucoamylase digests starch, and Sucrase digests sucrose.

Concept Tested & Keywords

Concept Tested: Biochemistry of carbohydrate digestion and related enzyme deficiencies.
Stem keywords: Lactose intolerance, enzyme deficiency
Lead-in keywords: caused by

QNsNJDF28haA7ol6g1JyG0

E6 Medicine Harrison 22e Part 2 p. 449-451

E6 Medicine Davidson Principles Practice 24e p. 832-834

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 129-131

Practise the full NVS- 2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.