Fragile X syndrome

The fragile X syndrome is said to be the most common heritable cause of mental retardation after Down's syndrome. It is caused by a dominant X-linked gene with a penetrance of only 50% in females.

The gene which is most commonly responsible is FMR-1 (familial mental retardation 1). The disease occurs when the expression of FMR-1 is disrupted by:

• a large number, more than 230, of trinucleotide repeats
• a deletion (rare)

It seems that loss of fmr-1 results in the fragile X syndrome. Common presenting symptoms include: (2)

• developmental delays
• intellectual disabilities
• premature ovarian failure
• fragile X-associated tremor/ataxia syndrome (FXTAS)
• autistic behaviours (eg, hand flapping, performing repetitive tasks)
• seizures
• anxiety and depression
• attention-deficit/hyperactivity disorder (ADHD) symptoms
• sleep disturbance
• aggression
• poor eye contact

advice from the UK National Screening Committee on antenatal screening for Fragile X syndrome..click here

Reference

1. Protic D et al. Fragile X Syndrome: From Molecular Aspect to Clinical Treatment. Int J Mol Sci. 2022 Feb 9;23(4):1935.
2. Moeschler JB, Shevell M., Committee on Genetics. Comprehensive evaluation of the child with intellectual disability or global developmental delays. Pediatrics. 2014 Sep;134(3):e903-18