Development of Novel Diagnostics for Fragile X Syndrome

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DESCRIPTION (provided by applicant): Fragile X Syndrome (FRAX), is the most common cause of mental retardation in males. The incidence of FRAX is 1 per 4000 in males and 1 per 8000 in females. FRAX is caused by the expansion of a CGG trinucleotide repeat of the 5' untranslated region (UTR) of FMR1 gene. This gene is located at chromosome Xq27.3. In normal individuals, the 5' UTR of the FMR1 gene contains 5 to 45 CGG repeats. However, over 200 repeats are found in individuals with FRAX. Presently, Southern Blot analysis is used to examine the size of the repeat segment and methylation status of the FRAX gene. Yet, this test only detects the gross size of CGG repeats and is highly labor intensive and expensive. PCR analysis can be used to examine the size of CGG repeats. This approach is limited, as the PCR reaction fails to amplify long stretches of CGG expansions. Recently, we developed a novel, highly efficient, accurate, test for diagnosing FRAX. This test relies on amplifying CGG repeat expansions by Site Specific Multiple Displacement Amplification (SSMDA), which capably amplifies very long stretches of GC-rich regions in the genome. SSMDA is followed by quantitative assessment of the numbers of CGG triplet repeats using real-time Polymerase Chain Reaction. We hypothesize that using this new molecular-based screening method, we can develop an effective, rapid and low-cost screening test for FRAX with broad commercial application. We anticipate that this Phase 1 application will lead to the development of a new screening procedure for FRAX that is sensitive, accurate, inexpensive, and adaptable for high-throughput use. If successful, we anticipate these Phase 1 studies will lead to Phase 2 studies. If broadly applied, this strategy will be applicable for diagnosing carriers of FRAX and individuals with FRAX.