**Core Concept**
Nieman Pick disease is a group of genetic disorders characterized by the accumulation of lipids, particularly sphingomyelin, in cells and tissues. This accumulation is due to a deficiency of a specific enzyme involved in lipid metabolism.

**Why the Correct Answer is Right**
The correct answer is correct because Nieman Pick disease is caused by a deficiency of acid sphingomyelinase (ASM), an enzyme that breaks down sphingomyelin into ceramide and phosphocholine. This deficiency leads to the accumulation of sphingomyelin in cells, particularly in the brain, liver, and spleen, resulting in the characteristic symptoms of the disease. The absence of ASM activity is due to mutations in the SMPD1 gene, which encodes the enzyme.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Alport syndrome is a genetic disorder caused by mutations in the COL4A3, COL4A4, or COL4A5 genes, affecting the production of type IV collagen.
**Option B:** This option is incorrect because Fabry disease is caused by a deficiency of alpha-Galactosidase A, an enzyme involved in the breakdown of certain lipids.
**Option C:** This option is incorrect because Tay-Sachs disease is caused by a deficiency of hexosaminidase A, an enzyme involved in the breakdown of gangliosides.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that Nieman Pick disease is a lysosomal storage disorder, and its diagnosis is confirmed by measuring the activity of acid sphingomyelinase in leukocytes or fibroblasts.

**Correct Answer: C. Acid sphingomyelinase deficiency.**