Fragile X syndrome: the most common inherited cause of intellectual disability
Fragile X syndrome is the most common inherited cause of intellectual disability. It results from expansion of CGG repeats in the FMR1 gene on the X chromosome. When the expansion is large enough, the gene no longer functions properly.
The body consequently produces too little FMRP, a protein important for brain development and communication between neurons. Because the condition is X-linked, it is usually more frequent and severe in males, although females may also be affected.
How does it present?
Manifestations vary and may include developmental delay, learning difficulties, intellectual disability and speech or behavioral problems. Some physical features become more apparent with age but cannot confirm the diagnosis alone.
Autism spectrum disorder, anxiety, attention difficulties and sensory sensitivity are common associations. Each person has a different profile of strengths and support needs.
What does carrying a premutation mean?
Some people have more CGG repeats than usual but not enough to cause the full syndrome. This premutation can expand in later generations, especially through maternal transmission, and may be associated in adulthood with fragile X-associated tremor/ataxia syndrome (FXTAS).
Molecular diagnosis
Diagnosis uses a DNA test that counts CGG repeats in FMR1 and evaluates other changes that may silence it. Testing should be considered for children with unexplained developmental delay, intellectual disability or autism.
Confirmation also enables genetic counseling, identification of other potential carriers and informed reproductive decisions.
Support and management
There is currently no curative treatment. Management supports development and independence through speech therapy, occupational therapy, specialized education and interventions tailored to behavioral or emotional needs.
Early intervention and a coordinated plan involving family, school and health professionals can substantially improve learning, communication and quality of life.
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This article provides general educational information and does not replace an individual medical assessment.