Fragile X syndrome is the leading inherited cause of intellectual disability, as well as the source of many cases of learning disabilities and autism. The syndrome affects both males and females, although males are typically more severely affected. In addition to learning difficulties, children with fragile X often suffer from hyperactivity, social anxiety, hypersensitivity to sensory stimuli, and autism and autistic-like behaviors, all of which limit their social and academic progress, create challenges for teachers, and are a source of stress and uncertainty for their families.
Fragile X is caused by a repetitive genetic error on the long arm of the X chromosome. The mutation is in a single gene called FMR1. A small set of nucleotides (the building blocks of DNA) are repeated excessively, disrupting the structure of the gene and preventing the production of its normally encoded protein (FMRP). The mutation is passed through families and can occur more frequently or severely in future generations.