A 15 year old boy has bilateral optic atrophy, diabetes mellitus and diabetes insipidus. The diagnosis is-
**Core Concept**
Optic atrophy, diabetes mellitus, and diabetes insipidus are manifestations of a rare genetic disorder caused by mutations in a specific gene, leading to impaired function of a crucial enzyme. This enzyme plays a vital role in the metabolism of a key compound, resulting in the observed clinical symptoms.
**Why the Correct Answer is Right**
The correct diagnosis is due to the presence of bilateral optic atrophy, which indicates damage to the optic nerves. Diabetes mellitus suggests impaired insulin secretion or action, while diabetes insipidus is characterized by the inability to regulate fluids due to a deficiency of antidiuretic hormone (ADH). These symptoms are classically associated with a deficiency of the enzyme 3-beta-hydroxysteroid dehydrogenase (3-beta-HSD), which is involved in the biosynthesis of steroids from cholesterol. The mutation affects the function of this enzyme, leading to the observed clinical manifestations.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not account for the presence of diabetes mellitus and diabetes insipidus, which are not typically seen in this condition.
**Option B:** This option is incorrect as it does not explain the bilateral optic atrophy, which is a key feature of the correct diagnosis.
**Option C:** This option is incorrect as it does not account for the specific combination of symptoms and the underlying genetic defect.
**Clinical Pearl / High-Yield Fact**
This condition is a classic example of a genetic disorder affecting multiple organ systems, highlighting the importance of considering the overall clinical picture when making a diagnosis. It also underscores the need for a thorough family history and genetic testing in cases where a specific diagnosis is not immediately apparent.
**Correct Answer:** C. Laurence-Moon-Bardet-Biedl syndrome