## **Core Concept**
The question revolves around a condition where a 6-month-old child experiences episodes of vomiting after consuming fruit juice. This scenario suggests an issue with metabolizing certain components found in fruit juice, likely related to an enzyme deficiency.

## **Why the Correct Answer is Right**
The correct answer, **Fructose-1-phosphate aldolase (Aldolase B)**, is related to the metabolism of fructose. Fructose-1-phosphate aldolase, also known as aldolase B, is an enzyme crucial for the breakdown of fructose in the liver. A deficiency in this enzyme leads to hereditary fructose intolerance (HFI), a condition where individuals cannot properly metabolize fructose. When children with HFI ingest fructose-containing foods, such as fruit juice, they experience symptoms like vomiting, hypoglycemia, and can progress to more severe complications.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Glucose-6-phosphatase deficiency leads to von Gierke's disease, primarily affecting glucose metabolism and leading to symptoms like hypoglycemia, hepatomegaly, and lactic acidosis, not specifically triggered by fruit juice consumption.
- **Option B:** Lactase deficiency leads to lactose intolerance, causing symptoms like bloating, gas, and diarrhea after consuming lactose-containing products, not specifically related to fruit juice ingestion.
- **Option C:** Sucrase-isomaltase deficiency causes problems with the digestion of sucrose and certain other carbohydrates, leading to symptoms like diarrhea and bloating after consuming sucrose-containing foods.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with hereditary fructose intolerance (HFI) often exhibit a aversion to fruits and sweets due to the gastrointestinal symptoms they experience upon ingestion, which can be a critical clue in the diagnosis. The diagnosis of HFI can be confirmed through genetic testing or a specific enzyme assay.

## **Correct Answer:** D. Fructose-1-phosphate aldolase.