Method of Diagnosis (testing, samples, etc.)
Diagnostic Testing
Is fragile x syndrome inherited?
This condition is inherited in an X-linked dominant pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. The inheritance is dominant if one copy of the altered gene in each cell is sufficient to cause the condition. In most cases, males experience more severe symptoms of the disorder than females. A striking characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.
Testing Strategy
- Targeted mutation analysis to the trinucleotide repeat region of FMR1.
- If this testing is normal and family history or clinical findings are very suspicious for Fragile X, a referral to genetics professional is helpful.
Unhelpful Tests
- Chromosome analysis with specialized culture techniques to identify fragile sites is no longer used to rule out fragile X syndrome, due to expense and low sensitivity.
- SNP microarrays used to detect genetic variations associated with developmental disability are NOT sensitive for Fragile X.
- Neuroimaging is of limited utility in diagnosis or management of Fragile X syndrome, but may be indicated in evaluation for Fragile X-Associated Tremor/Ataxia Syndrome.
Differential Diagnosis
Developmental delay/intellectual disability/behavioral issues differential
- Other chromosome abnormalities
- Sotos syndrome
- Prader-Willi syndrome
- Other causes of autism
- Other causes of ADHD Attention problems and hyperactivity are frequent in individuals with fragile X syndrome.
- Fragile XE syndrome (FRAXE)