## **Core Concept**
Tay-Sachs disease is a genetic disorder caused by a deficiency of the enzyme **hexosaminidase A (Hex-A)**, leading to the accumulation of certain lipids in the brain and other tissues. This condition is classified as a **lysosomal storage disease**. The substrate that accumulates due to the enzymatic deficiency is a type of ganglioside.

## **Why the Correct Answer is Right**
The correct answer, **GM2 ganglioside**, accumulates in Tay-Sachs disease because hexosaminidase A is required for its breakdown. Normally, hexosaminidase A cleaves the terminal **N-acetylgalactosamine** from GM2 ganglioside, allowing it to be further metabolized and excreted. Without sufficient hexosaminidase A activity, GM2 ganglioside accumulates within neurons, leading to cellular dysfunction and death.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a substance known to accumulate in Tay-Sachs disease.
- **Option B:** This option is incorrect as it refers to a different substance and not the one specifically associated with Tay-Sachs disease.
- **Option D:** This option is incorrect because it does not correspond to the substance that accumulates due to the deficiency of hexosaminidase A.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Tay-Sachs disease presents with severe neurological deterioration, including **macrocephaly**, **cherry-red spots** on the macula, and **spasticity**. Early diagnosis through genetic testing is crucial for family planning and management.

## **Correct Answer:** . GM2 ganglioside