It results from a mutation in a gene called FMR1 that is located on the X chromosome. Features of the syndrome may include mental retardation, learning disabilities, autism, behavioral problems, poor sensory perception and integration of information, and specific physical characteristics. The physical and developmental characteristics of Fragile X syndrome are not obvious at birth.
Physical growth occurs at an average, or above average, rate.
However, psychomotor development is delayed, and affected children show delays in smiling, recognizing their parents, rolling over, sitting up, and walking. Speech is especially affected and is frequently one of the symptoms that brings the family to see a developmental specialist. Frequently, affected children have large ears, a long face, a prominent forehead, long limbs, hypotonia or floppiness of the muscles, and large testicles that become more noticeable after puberty. Fragile X syndrome results from a mutation, or change, in a gene called FMR1 that is located on the X chromosome. The Fragile X mutation consists of an expansion, or an increase in the size of a portion of the FMR1 gene.