The Question is from neet-zoology chemical-coordincation-and-integration , and it was created by the author T SAILAJA

Question

A mutation in the gene encoding for 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) results in apparent mineralocorticoid excess (AME). This is because:

T SAILAJA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
 **Primary Concept**: Mineralocorticoid receptor function and regulation
 **Related Topics**:  Steroid hormone metabolism, aldosterone, cortisol, sodium reabsorption, apparent mineralocorticoid excess (AME)
 **Prerequisites**: Understanding of steroid hormone action, enzyme function, and kidney physiology.
## SOLUTION PATHWAY
**Given Information**:
  A mutation in the gene encoding for 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) causes AME.
  11β-HSD2 converts cortisol to cortisone.
**Method & Steps**:
 1. Understand the role of 11β-HSD2:
  Reasoning: 11β-HSD2 is an enzyme primarily located in the kidneys. Its function is to inactivate cortisol by converting it to cortisone. Cortisol has a similar affinity to mineralocorticoid receptors (MRs) as aldosterone, but cortisone does not.
  Formula/Rule:  None directly applicable.
 2. Consider the consequence of 11β-HSD2 mutation:
  Working: A mutation in the 11β-HSD2 gene leads to a loss or reduction in its enzyme activity. This means less cortisol is converted to cortisone.
  Key Point:  The unmetabolized cortisol can then bind to mineralocorticoid receptors (MRs) in the kidneys, mimicking the effects of aldosterone. 
 3. Relate to AME:
  Result:  The increased binding of cortisol to MRs leads to increased sodium reabsorption and potassium excretion, similar to the effects of excess aldosterone, resulting in apparent mineralocorticoid excess (AME).
  Verification: This explanation aligns with the known pathophysiology of AME.
 ## OPTION ANALYSIS
A :x: Aldosterone production is increased.  AME is not caused by increased aldosterone production, but by increased cortisol activity at the MR.
B ✓: Cortisol is not converted to cortisone in the kidney, allowing it to bind to mineralocorticoid receptors. This accurately describes the mechanism of AME in 11β-HSD2 deficiency.
C :x: The kidneys become insensitive to aldosterone.  The kidneys are not insensitive to aldosterone; rather, the problem is the excess activity of cortisol at the MR.
D :x: Sodium reabsorption in the kidneys is inhibited.  Sodium reabsorption is actually *increased* in AME due to the excess cortisol activity.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the roles of aldosterone and cortisol: Remember that both hormones can bind to mineralocorticoid receptors, but 11β-HSD2 helps regulate the amount of cortisol available to bind.
  2.Thinking that AME is caused by a primary defect in aldosterone production:  The excess mineralocorticoid effect is due to the action of cortisol.
 **Quick Tips**:
  1.Remember the key function of 11β-HSD2: converting cortisol to cortisone. 
  2.Visualize the competition between cortisol and aldosterone for the mineralocorticoid receptor.

T SAILAJA · Answer

Aldosterone production is increased.

T SAILAJA · Answer

The correct Option is "Cortisol is not converted to cortisone in the kidney, allowing it to bind to mineralocorticoid receptors."

T SAILAJA · Answer

The kidneys become insensitive to aldosterone.

T SAILAJA · Answer

Sodium reabsorption in the kidneys is inhibited.

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