Fragile X syndrome (FXS) is a rare genetic condition that affects approximately 1 in 4,000 to 5,000 boys and 1 in 8,000 girls. It is estimated to affect about 110,000 people in Europe and about 70,000 people in the US.
FXS is caused by a mutation of the FMR1 gene that provides instructions for production of a protein called Fragile X Mental Retardation Protein or FMRP. This protein plays a key role in developing synapses, the connections between nerve cells that relay nerve signals. Inadequate or disrupted FMRP production affects nervous system function, leading to both cognitive and behavioral issues.