New Test Identifies Fragile X Syndrome

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Testing for fragile X syndrome, the most common cause of inherited mental impairment, is expensive and time-consuming, which greatly limits its availability. Now a new, highly accurate and less costly test has been developed that can not only identify fragile X syndrome in infants but also single out couples who carry the gene.

Changes in the FMR1 gene is the characteristic shared by the family of genetic conditions known as fragile X. According to the National Fragile X Foundation, fragile X includes three conditions. Fragile X syndrome is the most common cause of inherited mental impairment, which can range from learning disabilities to more severe intellectual or cognitive problems. Fragile X syndrome is the most common known cause of autism or autistic-like behaviors.

Two less common disorders include fragile X-associated primary ovarian insufficiency, which can result in infertility and early menopause in some female gene carriers; and fragile X-associated tremor/ataxia syndrome, a disorder that affects tremor, memory, and balance in some older male gene carriers.

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An estimated 1 in 300 to 400 couples in the United States may carry mutations of the FMR1 gene, a gene that is responsible for making a protein critical for proper brain development. About 1 in 4,000 males are born with fragile X syndrome, and although it also impacts females, the severity of mental impairment is less. Because of cost and time limitations, screening for the syndrome is generally limited to couples who are believed to be at high risk.

Now a new study, lead by Feras M. Hantash, MS, PhD, of Quest Diagnostics in San Juan Capistrano, California, has resulted in a new test for fragile X syndrome that allows clinicians to identify gene mutations that cause the syndrome as well as milder gene expansions called premutations. The test utilizes polymerase chain reaction (PCR) technology, which the scientists found is capable of detecting FMR1 features called mosaics. These are difficult to identify using standard methods.

When compared with the current standard testing procedure for fragile X syndrome in 1,275 blood samples, the new PCR approach demonstrated 100 percent agreement. When abnormal results are found on the new fragile X syndrome test, further evaluation would be done, including the standard Southern blot test. The scientists believe that with additional study, the new PCR test may open the door for routine screening of newborns.

The study’s authors estimate that the new test could nearly eliminate the need for the number of Southern blot tests performed, which would result in significant savings in money and time. Before the American College of Medical Genetics and other organizations can officially recommend the new fragile X syndrome test for prenatal screening, however, additional research is necessary.

SOURCES:
American College of Medical Genetics
National Fragile X Foundation

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