A 3-year-old girl has been a fussy eater since being weaned, particularly when fruit is part of her diet. She would get cranky, sweat, and display dizziness, and lethargy, after eating a meal with fruit. Her mother noticed this correlation, and as long as fruit was withdrawn from her diet, the child did not display such symptoms. The problems the girl exhibits when eating fruit is most likely due to which one of the following?

**Core Concept**
The girl's symptoms are indicative of an adverse reaction to a specific compound present in fruit, which is a common allergen or intolerance. This condition is characterized by a deficiency of an enzyme crucial for the metabolism of this compound.

**Why the Correct Answer is Right**
The girl's symptoms, such as crankiness, sweating, dizziness, and lethargy after consuming fruit, are classic signs of an adverse reaction to fructose, a sugar found in many fruits. Fructose is typically metabolized by the enzyme fructokinase, which then converts it into fructose-1-phosphate. However, some individuals have a deficiency of the enzyme fructose-1-phosphate aldolase (also known as aldolase B), leading to the accumulation of fructose-1-phosphate and subsequent symptoms. This condition is known as hereditary fructose intolerance (HFI).

**Why Each Wrong Option is Incorrect**
**Option A:** Fructose malabsorption is a condition where individuals have difficulty absorbing fructose in the small intestine, leading to bloating, gas, and diarrhea. This is not the same as hereditary fructose intolerance, where the enzyme deficiency leads to metabolic problems.

**Option B:** Lactose intolerance is a condition where individuals are unable to digest lactose due to a deficiency of the enzyme lactase. This is unrelated to the girl's symptoms, which are specifically related to fruit consumption.

**Option C:** Celiac disease is an autoimmune disorder that causes the immune system to react to gluten, leading to small intestine damage and malabsorption. This is not related to the girl's symptoms, which are specifically related to fruit consumption.

**Clinical Pearl / High-Yield Fact**
Hereditary fructose intolerance is a rare genetic disorder that can lead to severe symptoms if left untreated. It is essential to recognize this condition and implement a strict fructose-free diet to prevent long-term complications.

**Correct Answer: C. Hereditary fructose intolerance.**

✓ Correct Answer: D. Elevated levels of fructose-1-phosphate in liver cells