In Fragile X syndrome, which gene shows hypermethylation leading to gene silencing?

In Fragile X syndrome, the gene that exhibits hypermethylation leading to its silencing is the FMR1 gene. This gene is critical because it encodes the Fragile X mental retardation protein, which plays a role in neuron function and development. In individuals with Fragile X syndrome, a CGG trinucleotide repeat in the FMR1 gene becomes expanded beyond the normal range, which triggers hypermethylation of the gene's promoter region. This hypermethylation prevents the transcription of the FMR1 gene, effectively silencing it. As a result, the lack of FMRP leads to the cognitive and developmental challenges associated with Fragile X syndrome.

The other genes mentioned—BRCA1, TP53, and CFTR—are associated with different conditions and do not play a role in Fragile X syndrome. BRCA1 is linked to breast and ovarian cancer, TP53 is a tumor suppressor gene involved in cancer, and CFTR is associated with cystic fibrosis. Therefore, in the context of Fragile X syndrome, FMR1 is the gene that undergoes hypermethylation, making it the correct answer.