A severely retarded infant is noted to have hepatosplenomegaly and a cherry-red spot in the macula. Of the following, which is most likely the cause of these findings?
**Core Concept**
The underlying condition is a lysosomal storage disorder characterized by the accumulation of a particular type of lipid in the cells, leading to cellular dysfunction and organ enlargement.
**Why the Correct Answer is Right**
The correct answer is related to Tay-Sachs disease, a genetic disorder caused by a deficiency of the enzyme hexosaminidase A (Hex-A). This enzyme is responsible for breaking down GM2 gangliosides, a type of lipid found in the brain and other tissues. Without Hex-A, GM2 gangliosides accumulate in neurons and other cells, leading to cellular damage and the characteristic cherry-red spot in the macula, as well as hepatosplenomegaly and severe mental retardation.
**Why Each Wrong Option is Incorrect**
* **Option A:** Niemann-Pick disease is another lysosomal storage disorder, but it is caused by a deficiency of the enzyme sphingomyelinase, which breaks down sphingomyelin, not GM2 gangliosides.
* **Option B:** Fabry disease is an X-linked recessive disorder caused by a deficiency of the enzyme alpha-Gal A, which breaks down globotriaosylceramide. It does not present with a cherry-red spot in the macula.
* **Option D:** Hurler syndrome is a mucopolysaccharidosis caused by a deficiency of the enzyme alpha-L-iduronidase, which breaks down dermatan and heparan sulfates. It does not present with the characteristic cherry-red spot in the macula.
**Clinical Pearl / High-Yield Fact**
Lysosomal storage disorders are a group of conditions characterized by the accumulation of lipids or mucopolysaccharides in cells, leading to cellular dysfunction and organ enlargement. Understanding the specific enzyme deficiencies and lipid/mucopolysaccharide accumulations is crucial for diagnosing and managing these conditions.
**Correct Answer:** C. Tay-Sachs disease.