## **Core Concept**
Regression of milestones refers to the loss or reversal of developmental achievements or skills that were previously acquired. This phenomenon is often observed in neurological or developmental disorders.

## **Why the Correct Answer is Right**
The correct answer, , is associated with a condition where there is typically no regression of milestones.

## **Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because it represents a condition known for regression of milestones.
* **Option B:** is incorrect because it is also associated with regression of milestones.
* **Option C:** is incorrect as it too involves regression of milestones.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in **Rett syndrome**, a neurodevelopmental disorder, there is a notable regression of milestones, particularly in girls. This condition leads to loss of social and language skills.

## **Correct Answer:** .