## Core Concept
Fructose intolerance, also known as hereditary fructose intolerance (HFI), is a genetic disorder caused by the deficiency of an enzyme involved in the metabolism of fructose. This condition leads to an inability to properly break down fructose, resulting in severe symptoms upon fructose ingestion. The enzyme deficiency associated with this condition is crucial for the utilization of dietary fructose.

## Why the Correct Answer is Right
The correct answer, **Aldolase B**, is the enzyme deficient in individuals with hereditary fructose intolerance. Aldolase B is crucial for the metabolism of fructose in the liver, where it catalyzes the conversion of fructose-1-phosphate into glyceraldehyde and dihydroxyacetone phosphate. This step is essential for the further metabolism and utilization of fructose. A deficiency in aldolase B leads to the accumulation of toxic intermediates when fructose is ingested, causing symptoms such as vomiting, hypoglycemia, and liver dysfunction.

## Why Each Wrong Option is Incorrect
- **Option B: Glucose-6-phosphatase** - This enzyme is involved in glucose metabolism, specifically in the gluconeogenic pathway and glycogenolysis, and its deficiency leads to von Gierke's disease, a different metabolic disorder.
- **Option C: Fructokinase** - While involved in fructose metabolism by phosphorylating fructose to fructose-1-phosphate, its deficiency leads to essential fructosuria, a benign condition different from hereditary fructose intolerance.
- **Option D: Lactase** - This enzyme is involved in carbohydrate digestion in the intestine, breaking down lactose into glucose and galactose. Its deficiency leads to lactose intolerance, unrelated to fructose metabolism.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that patients with hereditary fructose intolerance must strictly avoid dietary fructose to prevent acute symptoms and long-term complications. This condition is diagnosed through genetic testing and enzyme assays, and management involves a fructose-free diet.

## Correct Answer: A. Aldolase B