**Core Concept**
I-cell disease, also known as mucolipidosis II, is a rare genetic disorder characterized by the accumulation of mucolipids within cells due to a deficiency in the enzyme N-acetylglucosaminyl-phosphotransferase. This enzyme is crucial for the proper glycosylation and targeting of lysosomal enzymes to the lysosome.

**Why the Correct Answer is Right**
I-cell disease is characterized by the presence of I-cell fibroblasts, which are cells that contain abnormal lysosomes. These cells are unable to properly target lysosomal enzymes to the lysosome, leading to their accumulation in the endoplasmic reticulum. The disease is also associated with the presence of sialylated, mannose-rich oligosaccharides on the surface of I-cell fibroblasts. This is due to the abnormal glycosylation of proteins, which is a result of the deficiency in N-acetylglucosaminyl-phosphotransferase.

**Why Each Wrong Option is Incorrect**
* **Option A:** The accumulation of mucolipids in I-cell disease is indeed a characteristic of the disease, making this option incorrect.
* **Option B:** The presence of I-cell fibroblasts is a hallmark of I-cell disease, so this option is also incorrect.
* **Option D:** The disease is associated with the accumulation of sialylated, mannose-rich oligosaccharides on the surface of I-cell fibroblasts, making this option incorrect as well.

**Clinical Pearl / High-Yield Fact**
I-cell disease is often confused with Hurler syndrome, which is also a type of mucopolysaccharidosis. However, I-cell disease is a distinct entity with a different underlying pathophysiology.

**Correct Answer: A.**