**Core Concept**
GM2 gangliosidosis is a group of lysosomal storage disorders caused by the deficiency of the enzyme beta-hexosaminidase (Hex-B). This enzyme is responsible for the breakdown of a specific ganglioside, GM2, in the brain and peripheral nerves.

**Why the Correct Answer is Right**
The deficiency of Hex-B leads to the accumulation of GM2 ganglioside within neurons, causing progressive neurodegeneration and clinical manifestations such as seizures, ataxia, and dementia. This accumulation is due to the inability of the cell to break down the GM2 ganglioside, resulting in cellular dysfunction and death. The Hex-B enzyme is critical for the normal functioning of the lysosomal compartment, and its deficiency has severe consequences for the cell.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Sandhoff disease is another type of GM2 gangliosidosis, but it is caused by the deficiency of both Hex-A and Hex-B enzymes.

**Option B:** This option is incorrect because Fabry disease is a lysosomal storage disorder caused by the deficiency of alpha-Gal A enzyme, not Hex-B.

**Option C:** This option is incorrect because Tay-Sachs disease is another type of GM2 gangliosidosis, but it is caused by the deficiency of the Hex-A enzyme.

**Clinical Pearl / High-Yield Fact**
The Hex-B enzyme is a heterodimer composed of a heavy chain and a light chain, and its deficiency is associated with a more severe clinical phenotype compared to Hex-A deficiency.

**Correct Answer:** C. Tay-Sachs disease.