Molecular Profiling Characterizes Fragile X Syndrome

An advanced polymerase chain reaction (PCR) method demonstrates comprehensive molecular profiling of the Fragile X Mental Retardation (FMR1) gene.

Fragile X is a trinucleotide repeat disease caused predominantly by the expansion of CGG sequences in the 5' untranslated region of the FMR1 gene. The specific number of CGG repeats is associated with a constellation of disorders that can affect patients both young and old.

This assay supports two different PCR formats, Gene-specific FMR1 PCR and CGG Repeat Primed (RP) PCR, that both enable the detection of alleles across the full range of CGG repeats and accurately differentiate female heterozygous and homozygous samples. Either PCR format can reduce the number of samples required for Southern blot analysis by as much as 50-fold.

The innovative technology is produced by Asuragen, Inc (Austin, TX, USA). Two recent studies, carried out at the University of California at Davis (UCDavis; USA), and the Rush University Medical Center (Chicago, IL, USA), significantly demonstrated that Asuragen's PCR technologies offered sensitive, specific, and robust detection of fragile X expanded alleles, and more informative genotyping data than existing methods.

Flora Tassone, Ph.D., at UCDavis said, "Based upon the results with more than 170 unique samples, including 75 full mutations, it is clear that the CGG repeat primed PCR represents a substantial improvement over current approaches for FMR1 molecular assessments." Fragile X Syndrome (FXS) is one of several disorders linked to the expansion of CGG repeat sequences in the 5' untranslated region of FMR1. Expansion to >200 triplet repeats often results in FXS, which affects about 1 in 5,000 individuals and is a leading cause of autism and the most common form of inherited intellectual disability. One study was published online in the July 2010 issue of Journal of Molecular Diagnostics.

The assay definitively resolves zygosity in female samples and can rule out samples that would otherwise be needlessly analyzed by Southern blot. Lastly, the PCR can reveal both the number and sequence context of interrupting AGG elements that may impact the risk of CGG expansion in the next generation. Although fragile X disorders impact more than one million people in the U.S. alone, the vast majority of individuals at risk are unaware of their fragile X status. Current testing methods include Southern blot analysis, are low throughput, time-consuming, and provide limited molecular information about the fragile X gene.


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