Sandhoffs disease is d/t absence of which enzyme?
**Core Concept**
Sandhoff disease is a rare, inherited lysosomal storage disorder characterized by the accumulation of gangliosides within neurons, leading to neurodegeneration. It is caused by a deficiency in a specific enzyme involved in the breakdown of these complex lipids.
**Why the Correct Answer is Right**
Sandhoff disease is caused by a deficiency in the enzyme beta-hexosaminidase B (Hex-B), which is responsible for hydrolyzing the ganglioside GM2. The absence of this enzyme leads to the accumulation of GM2 ganglioside within neurons, causing cellular damage and ultimately, neurodegeneration. This deficiency is due to mutations in the HEXB gene, which codes for the Hex-B enzyme.
**Why Each Wrong Option is Incorrect**
**Option A:** **Hex-A**, while related to Sandhoff disease, is not the enzyme responsible for the disease. Hex-A is another enzyme involved in ganglioside breakdown, but its deficiency leads to Tay-Sachs disease, a different lysosomal storage disorder.
**Option B:** **Sphingomyelinase** is an enzyme involved in the breakdown of sphingomyelin, another type of lipid. Its deficiency leads to Niemann-Pick disease, a different lysosomal storage disorder.
**Option C:** **Acid alpha-glucosidase** is an enzyme involved in the breakdown of glycogen. Its deficiency leads to Pompe disease, a different lysosomal storage disorder.
**Clinical Pearl / High-Yield Fact**
Sandhoff disease is a rare but severe form of lysosomal storage disorder, often presenting with severe neurodegeneration and death in early childhood. It is essential to distinguish it from other lysosomal storage disorders, such as Tay-Sachs disease, which has a similar clinical presentation but is caused by a deficiency in the Hex-A enzyme.
**Correct Answer: D. Hex-B, the beta-hexosaminidase B enzyme.**