Fragile X Carrier Screening

This test is designed to detect individuals at risk of transmitting Fragile X related FMR1 gene 5'UTR CGG repeat expansions. Fragile X syndrome is one of the most common forms of inherited intellectual disability. Fragile X syndrome is an X-linked disorder that affects both males and females, but males are usually more severely affected. In addition to developmental delay and intellectual disability, individuals with Fragile X syndrome often have behavioral issues, autism spectrum disorder, and characteristic facial features. In 99% of affected individuals, Fragile X syndrome (MIM 300624) is caused by expansion of the CGG repeat sequence in the 5%u2019UTR of the FMR1 gene (NM_002024) to greater than 200 repeats. This repeat expansion causes hypermethylation of the FMR1 gene, resulting in silencing of FMR1 gene expression. The interpretation of Fragile X test results is based on the number of CGG repeats detected, using the following ranges: <45 repeats is Negative, 45-54 repeats is the Intermediate range, 55-200 repeats is a Premutation, and >200 repeats is a Full Mutation. Individuals with <55 repeats are at low risk for having a child with Fragile X syndrome; however, intermediate alleles may expand into the premutation range in future generations. Fragile X expansions are transmitted from the mother; therefore, females with repeat numbers in the premutation range (55-200 repeats) are at risk of having a child with Fragile X syndrome. Additionally, females in the premutation range may have fragile X-associated primary ovarian insufficiency (MIM 300623) resulting in menopause before the age of 40. Males, and some females, in the premutation range may develop fragile X-associated tremor/ataxia syndrome (MIM 311360), a late onset disorder characterized by tremor, ataxia, and gradual cognitive decline. This test is intended for pre/post-conception carrier screening and is not intended for diagnostic testing.