What genetic alteration is primarily associated with Fragile X Syndrome?

The genetic alteration primarily associated with Fragile X Syndrome is the addition of more than 200 CGG repeats in the FMR1 gene. This repetitive expansion leads to the silencing of the FMR1 gene, resulting in a deficiency of the fragile X mental retardation protein (FMRP), which is crucial for normal neurodevelopment. Individuals with Fragile X Syndrome often exhibit cognitive impairments, behavioral challenges, and physical features associated with the condition.

In contrast, a deletion of the FMR1 gene, less than 200 CGG repeats, or a translocation of the FMR1 gene do not characterize Fragile X Syndrome. While the normal range of CGG repeats is usually about 5 to 44, and expansions up to 200 are considered pre-mutation, only repeats exceeding 200 lead to the full manifestation of the syndrome. Thus, understanding the specific genetic alteration helps in recognizing the mechanism behind the disorder and its clinical implications.