A 12 year old girl presents with tremors and emotional lability. Slit lamp examination of eye shows golden brown discoloration in the Descements membrane. What is the most appropriate diagnosis for this patient?
**Core Concept**
The patient's symptoms, particularly the golden brown discoloration in the Descemet's membrane on slit lamp examination, suggest a systemic disorder affecting the eyes and possibly other organs. This condition is related to a defect in the metabolism of a specific amino acid.
**Why the Correct Answer is Right**
The golden brown discoloration in the Descemet's membrane is characteristic of a condition known as **Hartnup disease**. This is a rare autosomal recessive disorder caused by mutations in the SLC6A19 gene, which encodes a neutral amino acid transporter. The condition leads to impaired absorption and metabolism of certain amino acids, including tryptophan, resulting in tryptophan deficiency. Tryptophan is an essential amino acid necessary for the production of niacin (vitamin B3) and serotonin. The deficiency of tryptophan leads to decreased niacin levels, causing pellagra-like symptoms, including dermatitis, diarrhea, dementia, and potentially, the eye discoloration seen in this patient.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not the correct diagnosis as it does not match the clinical presentation and slit lamp findings. The condition described in this option does not involve a defect in amino acid metabolism.
**Option B:** This option is incorrect as it does not explain the eye discoloration or the systemic symptoms of the patient.
**Option C:** This is not the correct diagnosis as it does not involve a defect in tryptophan metabolism or the characteristic eye findings.
**Clinical Pearl / High-Yield Fact**
The golden brown discoloration in the Descemet's membrane, known as **Hofmann-Waldenström's sign**, is a classic finding in Hartnup disease. This sign is often seen in patients with tryptophan deficiency and can be used as a diagnostic clue in cases of suspected Hartnup disease.
**Correct Answer: C. Hartnup disease.**