NOT a feature of Fragile X syndrome
**Core Concept**
Fragile X syndrome is a genetic disorder caused by a mutation in the FMR1 gene, leading to the absence of the fragile X mental retardation protein (FMRP). This protein plays a crucial role in regulating synaptic plasticity and neuronal development. The syndrome is characterized by intellectual disability, behavioral problems, and distinct physical features.
**Why the Correct Answer is Right**
The correct answer is a feature that is not typically associated with Fragile X syndrome. The FMRP deficiency leads to abnormal synaptic function, resulting in impaired learning and memory. Individuals with Fragile X syndrome often exhibit hyperactivity, anxiety, and attention deficit hyperactivity disorder (ADHD)-like symptoms. They may also display distinctive physical characteristics, such as a long face, prominent ears, and macroorchidism (enlarged testes) in post-pubertal males.
**Why Each Wrong Option is Incorrect**
**Option A:** Intellectual disability is a hallmark feature of Fragile X syndrome, resulting from the absence of FMRP, which is essential for normal brain development and function.
**Option B:** Hyperactivity and anxiety are common behavioral problems in individuals with Fragile X syndrome, often co-occurring with ADHD-like symptoms.
**Option C:** Macroorchidism is a characteristic physical feature of Fragile X syndrome, particularly in post-pubertal males, resulting from the FMRP deficiency.
**Clinical Pearl / High-Yield Fact**
Fragile X syndrome is the most common cause of inherited intellectual disability, accounting for approximately 30% of cases.
**Correct Answer: D.**