Fragile X syndrome (FXS)

Fragile X syndrome is an inherited genetic condition caused by changes in the FMR1 gene on the X chromosome and is the most common known inherited cause of intellectual disability.

The gene change silences production of a protein needed for normal brain development and synaptic function. Features include learning difficulties ranging from mild to severe, delayed speech, anxiety, hyperactivity, sensory sensitivity, hand flapping, avoidance of eye contact and, in many cases, autism spectrum disorder. Physical traits such as a long face, prominent ears and flexible joints become more apparent with age. Males are usually more severely affected than females.

Diagnosis is confirmed by a DNA blood test that counts the repeats in the FMR1 gene, and genetic counseling is offered to families because carriers can have related conditions later in life. Care involves early intervention, educational support, speech and occupational therapy and medication for specific symptoms. Cannabinoid-based products are under investigation for behavioral symptoms of fragile X syndrome, and clinical evidence remains limited.