What genetic mechanism is most directly implicated in Fragile X Syndrome?

Fragile X Syndrome is primarily associated with an expansion of CGG repeats within the FMR1 gene. In this genetic condition, the normal range of CGG repeats is typically between 5 to 44 repeats, while individuals with Fragile X Syndrome often have more than 200 repeats. This substantial expansion leads to hypermethylation of the FMR1 gene, which in turn causes silencing of the gene and subsequent deficiency in the fragile X mental retardation protein (FMRP). FMRP is crucial for normal brain development and function, and its absence is responsible for the cognitive and developmental challenges observed in affected individuals.

The mechanism of gene methylation is a significant feature in Fragile X, as the methylation directly correlates with the silencing of the FMR1 gene, leading to the neurodevelopmental phenotypes associated with this condition. This makes the option referencing CGG repeats and methylation the most accurate representation of the underlying genetic cause of Fragile X Syndrome.