Fragile X Syndrome is primarily caused by a mutation in which gene?

Fragile X Syndrome is primarily caused by a mutation in the FMR1 gene. This gene is located on the X chromosome and is responsible for producing a protein called FMRP, which is crucial for normal neuronal function and development. When this gene is mutated, it leads to a deficiency or absence of FMRP, which disrupts synaptic development and can result in the intellectual disabilities and developmental challenges associated with Fragile X Syndrome.

The other choices refer to different genetic locations or genes that do not contribute to Fragile X Syndrome. The 21st chromosome is primarily known for conditions like Down syndrome, while chromosome 15 is associated with Prader-Willi and Angelman syndromes, both of which are unrelated to Fragile X. The thyroid hormone gene also conveys no relationship to this syndrome, as it is involved in thyroid function rather than the specific neurological effects seen in Fragile X Syndrome. Understanding the specific genetic basis of Fragile X helps in diagnosis and managing the associated developmental and behavioral challenges.