**Core Concept**
Hexosaminidase A (Hex-A) is a lysosomal enzyme responsible for breaking down gangliosides, particularly GM2 ganglioside. The enzyme consists of two subunits: alpha (α) and beta (β). A deficiency in the alpha subunit leads to Tay-Sachs disease, while a deficiency in the beta subunit leads to a milder form of the disease.

**Why the Correct Answer is Right**
Hexosaminidase A's alpha subunit (Hex-Aα) is crucial for the breakdown of GM2 ganglioside. A deficiency in this subunit results in the accumulation of GM2 ganglioside within neurons, leading to neuronal degeneration and death. This is the hallmark of Tay-Sachs disease, characterized by progressive neurological deterioration, muscle weakness, and eventual death.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a deficiency in the beta subunit of hexosaminidase A leads to a milder form of the disease, known as Sandhoff disease.
* **Option B:** This option is incorrect because it does not specify the correct enzyme or subunit involved in the disease.
* **Option C:** This option is incorrect because it is not related to the hexosaminidase enzyme or its deficiency.

**Clinical Pearl / High-Yield Fact**
A deficiency in the alpha subunit of hexosaminidase A is a classic example of a lysosomal storage disorder, which can be inherited in an autosomal recessive pattern. Tay-Sachs disease is a devastating condition that highlights the importance of lysosomal function in maintaining neural health.

**Correct Answer: A. Deficiency of the alpha subunit of hexosaminidase A causes Tay-Sachs disease.**