Fragile X Syndrome - Genetic Testing
Test Information/Clinical Significance
Fragile X syndrome is a frequent form of intellectual disability. Affected individuals usually have normal physical features. Fragile X syndrome occurs in males and females with varying degrees of disability.
The Fragile X syndrome results from a change in the 5’ untranslated region of the FMR1 gene. Normally the FMR1 gene contains between 6 and 50 repeats of the CGG sequence. The number of repeats is passed down from generation to generation. Over generations, there may be a slow increase in the number of CGG repeats (from a “premutation” level to a higher level resulting in Fragile X syndrome. The increased number of CGG repeats results in instability of the gene.
When there are 50 to 200 repeats of the CGG sequence, affected males and females are usually intellectually normal. Greater than 200 repeats results in inactivation of the FMR1 gene and Fragile-X syndrome.
Nucleic acid amplification of the CGG triplet region detects alleles within the normal range. Specimens recording inconclusive results are further tested by a confirmatory method known as southern blotting.
Assay Method
Nucleic acid amplification and identification
Genetic Counselling
Genetic counselling is an essential aspect of testing for all genetic disorders and should be offered to patients prior to referral for testing and for discussion of test results.
Specimen
5 mL EDTA
Results Availability
Testing performed twice weekly