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Quest Pulls Ahead in Fragile X Test Race with NY State DoH Approval

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By Ben Butkus

Quest Diagnostics said this week that its laboratory-developed XSense test for fragile X syndrome has been approved by New York State's Department of Health.

With the approval, Quest can offer the test to physicians in New York as well as in all other US states, as New York is the only state with an independent regulatory review process for lab-developed tests, which are also regulated at the federal level under the Clinical Laboratory Improvement Amendments.

XSense is the first nucleic acid amplification-based test for fragile X syndrome to be approved by New York. Specifically, XSense uses triplet-primed PCR by capillary electrophoresis to assess the number of CGG repeats in the FMR1 gene on the X chromosome.

The number of CGG repeats an individual has in FMR1 is correlated with either a permutation, meaning they are a carrier; or a full mutation, meaning they have the disorder.

Quest introduced its test in February, and researchers collaborating with the company have published data supporting its potential use as a population screening tool for fragile X.

In a research paper published in March in Genetics in Medicine, Charles Strom and colleagues at the Quest Diagnostics Nichols Institute reported that the test showed 100 percent agreement with Southern blot tests in a panel of 1,275 blood samples. The test was also capable of detecting so-called "mosaic" patterns, which have been difficult to detect using traditional methods; and was able to detect mutations for fragile X in six of the 1,275 patients tested.

Southern blot has been regarded as the gold standard for fragile X testing, but can take several days to weeks to perform and is unsuitable for high-volume testing.

"New York's approval is significant because it means a new, highly innovative genetic analysis technique for fragile X has fulfilled state-required quality standards that are widely regarded in the lab industry as highly rigorous," Strom said in a statement.

Also, Quest noted that earlier this month researchers from Murdoch Childrens Research Institute in Australia published a study in Genetics in Medicine that found there is adequate research data to support population screening and diagnostic testing for the condition in a range of patients, including women and newborns.

A spokesperson for Quest said that the test's approval means that "the medical community can consider —for the first time — its options for implementing population screening for fragile X syndrome."

The approval would also seem to give Quest a leg up on competing companies and institutions developing PCR-based tests for fragile X.

These developers include Asuragen, which has developed a research-use only PCR kit for fragile X that uses triple-repeat primed PCR with proprietary gene-specific primers and amplification buffers for CG-rich templates; and the ARUP Institute for Clinical and Experimental Pathology at the University of Utah, which used analyte-specific reagents made by Celera and distributed by Abbott to develop its own triple repeat primed/capillary electrophoresis test with "laboratory-developed test" authorization under CLIA (PCR Insider, 5/20/10).

Both ARUP Labs and Asuragen continue to publish data supporting the efficacy of their tests and the general idea that PCR-based fragile X testing is suitable for population-based screening of carriers and newborns.

In an April study published in the Journal of Molecular Diagnostics, ARUP Institute and Celera showed that their test had 100 percent concordance with PCR/Southern blot analysis in 205 samples.

Meantime, a study published in March in Clinical Chemistry by researchers from Asuragen and the MIND Institute showed that their test could detect every one of 66 full mutations that were co-detected using Southern blot analysis across 146 clinical samples.

And this week, Asuragen announced the results of two new studies demonstrating the utility of its test. Results from the first study, conducted with the same researchers from the MIND Institute, were published online earlier this month in the Journal of Molecular Diagnostics and will appear in the September print version of the journal.

The second study, conducted in collaboration with Rush University Medical Center, reported results from an independent study of 41 clinical samples using a prototype high-resolution methylation PCR assay that can assess FMR1 methylation concordant with both Southern blot and patient phenotype, Asuragen said. The results of that study were presented at the International Fragile X Conference, held last week in Detroit.

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