Fragile X syndrome is primarily caused by what genetic factor?

Fragile X syndrome is primarily associated with a specific gene mutation that affects the FMR1 gene located on the X chromosome. In individuals with this condition, there is an expansion of a CGG trinucleotide repeat in the promoter region of the FMR1 gene. This sequence typically consists of 5 to 44 repeats in the general population, but in individuals with Fragile X syndrome, it can expand to over 200 repeats, which leads to methylation of the gene and subsequent silencing. This results in the absence of the fragile X mental retardation protein, which is crucial for normal cognitive and developmental function.

The other genetic factors mentioned are not responsible for Fragile X syndrome. Chromosomal deletion refers to a loss of a portion of a chromosome and is associated with various genetic disorders, but it does not apply here. Chromosomal inversion involves a segment of a chromosome being reversed end to end, which can also lead to genetic abnormalities, but this is not the mechanism behind Fragile X. Gene amplification involves an increase in the number of copies of a particular gene, a process that is unrelated to the specific mutation seen in Fragile X syndrome. Therefore, the gene mutation related to the methylation and expansion of the FMR1 gene is