Which is not true about Fragile X syndrome?
**Core Concept**
Fragile X syndrome is a genetic disorder caused by a mutation in the FMR1 gene on the X chromosome, leading to the absence or deficiency of the fragile X mental retardation protein (FMRP). This protein plays a crucial role in brain development and function, particularly in the regulation of synaptic plasticity and neuronal communication.
**Why the Correct Answer is Right**
Fragile X syndrome is characterized by a range of clinical features, including intellectual disability, behavioral problems, and physical characteristics such as a long face and large ears. The syndrome is caused by an expansion of a CGG repeat in the FMR1 gene, leading to hypermethylation and silencing of the gene. FMRP is essential for the regulation of mRNA transport and synaptic plasticity, and its deficiency is associated with abnormal neuronal development and function.
**Why Each Wrong Option is Incorrect**
**Option A:** Fragile X syndrome is not primarily caused by a mutation in the FMR2 gene, which is associated with the fragile X E syndrome. **Option B:** Fragile X syndrome is not characterized by an increase in muscle tone, as seen in cerebral palsy. **Option C:** Fragile X syndrome is not caused by a deletion of the FMR1 gene, but rather an expansion of the CGG repeat.
**Clinical Pearl / High-Yield Fact**
Fragile X syndrome is the most common cause of inherited intellectual disability, and it affects approximately 1 in 4000 males and 1 in 6000 females. It is essential to recognize the clinical features of the syndrome, including developmental delays, behavioral problems, and physical characteristics, to provide accurate diagnosis and management.
**Correct Answer:** None of the above