**Core Concept**
Mucopolysaccharidoses (MPS) are a group of genetic disorders caused by the deficiency of enzymes required for the breakdown and recycling of glycosaminoglycans (GAGs), leading to their accumulation in various tissues. This accumulation results in a range of clinical manifestations, including intellectual disability, skeletal abnormalities, and organ dysfunction.

**Why the Correct Answer is Right**
Mental retardation (now referred to as intellectual disability) is a characteristic feature of several MPS disorders, including MPS I (Hurler syndrome), MPS II (Hunter syndrome), MPS III (Sanfilippo syndrome), MPS IV (Morquio syndrome), and MPS VI (Maroteaux-Lamy syndrome). However, MPS VII (Sly syndrome) is an exception, as it primarily affects the lysosomal enzyme beta-glucuronidase, which is involved in the degradation of GAGs, but does not significantly impact cognitive function.

**Why Each Wrong Option is Incorrect**
* **Option A:** MPS I (Hurler syndrome) is characterized by severe intellectual disability, making it incorrect.
* **Option B:** MPS II (Hunter syndrome) also presents with intellectual disability, so it's not the correct answer.
* **Option C:** MPS IV (Morquio syndrome) can lead to intellectual disability, especially in the later stages of the disease, so it's not the correct choice.
* **Option D:** MPS VII (Sly syndrome) is the correct answer because it is the only MPS disorder that does not typically feature intellectual disability as a major symptom.

**Clinical Pearl / High-Yield Fact**
The clinical spectrum of mucopolysaccharidoses can vary significantly between different disorders, and a thorough understanding of each enzyme's role in GAG degradation is crucial for accurate diagnosis and management.

**Correct Answer: D. MPS VII (Sly syndrome)**