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
Reference
- Protic D et al. Fragile X Syndrome: From Molecular Aspect to Clinical Treatment. Int J Mol Sci. 2022 Feb 9;23(4):1935.
- 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
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