This article has been updated from a previous version to correct the names of the CE platforms used to run Asuragen's assay.
NEW YORK – The US Food and Drug Administration late on Friday authorized marketing of Asuragen’s AmplideX Fragile X Dx and Carrier Screen Kit, the first genetic test for fragile X syndrome (FXS).
The assay is intended to aid in diagnosing FXS and is to be used alongside the evaluation of a patient’s family history and clinical signs and symptoms, FDA said.
The test is also intended for use in adults who may be carriers of genetic alterations in FMR1, the gene associated with FXS.
According to the US Centers for Disease Control and Prevention, approximately 1 in 4,000 males and 1 in 8,000 females in the US have FXS, a genetic disorder caused by changes in the FMR1 gene located on the X chromosome. A segment of the FMR1 DNA, known as a CGG trinucleotide repeat, is repeated in excess on the X chromosome in individuals with the disorder.
While some repetition of the CGG repeat is normal, a high number of repeats may indicate potential health risks. Asuragen's test uses a method called triplet repeat primed PCR (TP-PCR) to measure the number of repeats of the CGG segment in the FMR1 gene using a patient blood sample. The test can determine whether the number of CGG repeats is considered normal, intermediate, premutation, or full mutation.
Individuals with a full mutation typically have FXS, which is associated with developmental delays, learning disabilities, social and behavioral issues, intellectual disabilities, and autism spectrum disorder. Women with a premutation have an increased risk of having a child with FXS, while men with a premutation will pass it to their daughters only. Individuals with normal or intermediate levels of repeated CGG segments are currently thought to be asymptomatic for FXS or other fragile X-associated disorders.
In addition to aiding in the diagnosis of FXS and for carrier testing, Asuragen's test can be used to help diagnose fragile X-associated disorders, including fragile X-associated tremor/ataxia syndrome, a movement and cognitive disorder that typically occurs in adults over age 50; and fragile X-associated primary ovarian insufficiency, a condition that is characterized by reduced function of the ovaries.
The FDA said that it reviewed data for the test through its de novo classification program for low- to moderate-risk devices of a new type. The agency evaluated data from two multi-center clinical validation studies conducted across three trial sites to determine that the assay has a diagnostic accuracy of greater than 95 percent. Asuragen noted that carrier screening performance for detection of premutations or full mutations had a positive percent agreement of 100 percent.
Asuragen had already been marketing AmplideX PCR/CE FMR1 reagents for detecting CGG repeats in the FMR1 gene in a research-use-only capacity. The Applied Biosystems 3500 Dx Genetic Analyzer and 3500xL Dx Genetic Analyzer from Thermo Fisher Scientific, which were FDA-cleared for fragment sizing in parallel with this test, are used to detect the DNA products amplified by TP-PCR. In 2017 Asuragen and Thermo Fisher Scientific began a collaboration around the commercialization of these products.
"AmplideX technology introduced a dramatic paradigm shift in how challenging repetitive sequences, like those within FMR1, could be routinely detected and analyzed," Elizabeth Berry-Kravis, co-investigator of the clinical study and codirector of the molecular diagnostics section of the genetics laboratory at Rush University Medical Center, said in a statement. "Enabling better access to testing to predict and diagnose these cases significantly improves our ability to make a difference in these patients' lives by eliminating the diagnostic odyssey that many families experience and allowing more accurate genetic counseling."