**Question:** All are features of Alpo syndrome, except:

A. Increased urine output
B. Polyuria
C. Diabetes insipidus
D. Hyponatremia

**Core Concept:** Alpo syndrome is a rare disorder characterized by increased urine output, polyuria, and hyponatremia, which can lead to osmotic diuresis and cerebral edema. It is caused by the inappropriate secretion of antidiuretic hormone (ADH) from the posterior pituitary gland, resulting in excessive water reabsorption in the nephron and low serum sodium levels.

**Why the Correct Answer is Right:** Alpo syndrome is characterized by the inappropriate secretion of ADH, which leads to increased water reabsorption, resulting in polyuria and hyponatremia. The correct answer, D (Hyponatremia), is indeed a feature of Alpo syndrome but is not specifically mentioned as an exclusion in the question.

**Why Each Wrong Option is Incorrect:**

A. Increased urine output: As Alpo syndrome is caused by inappropriate ADH secretion, increased urine output is expected in this condition. Thus, option A is incorrect.

B. Polyuria: Alpo syndrome leads to increased urine output due to excessive water reabsorption, which results in polyuria. This option is incorrect.

C. Diabetes insipidus: Diabetes insipidus is a condition characterized by excessive urine output due to impaired ADH secretion, not inappropriate ADH secretion as in Alpo syndrome. Therefore, option C is incorrect.

**Clinical Pearl:** Hyponatremia in Alpo syndrome is due to excessive water reabsorption, leading to an imbalance in electrolyte levels and cerebral edema in severe cases. It is essential for students to understand the underlying pathophysiology of this condition and differentiate it from other conditions like diabetes insipidus, which involves impaired ADH secretion.