Which gene mutation is closely associated with Fragile X syndrome?

Fragile X syndrome is most closely associated with mutations in the FMR1 gene. This gene is located on the X chromosome and is responsible for producing the FMRP (Fragile X Mental Retardation Protein), which plays a crucial role in neuronal development and function.

In individuals with Fragile X syndrome, there is typically a CGG trinucleotide repeat expansion within the FMR1 gene. When the number of repeats exceeds a certain threshold (usually over 200), it leads to methylation of the gene and subsequent silencing, resulting in the absence of functional FMRP. The lack of this protein affects synaptic function and is linked to the cognitive and behavioral features associated with Fragile X syndrome, including intellectual disability and autism spectrum disorders.

The other gene mutations listed do not have a direct connection to Fragile X syndrome. For instance, CFTR is associated with cystic fibrosis, F5 is related to clotting disorders, and H63D is a variant of the HFE gene linked to hereditary hemochromatosis. Therefore, the FMR1 gene is specifically implicated in Fragile X syndrome due to its vital role and the mechanism involved in the disorder.