FMR1 is a gene located on the X chromosome that plays a crucial role in the production of a protein called FMRP. This protein is important for normal brain development and function, particularly in the formation of synapses, which are connections between nerve cells. Mutations or expansions in the FMR1 gene can lead to Fragile X syndrome, a genetic condition that causes intellectual disabilities and developmental delays. This syndrome is the most common inherited cause of these issues and primarily affects males, although females can also be affected to a lesser degree.