Tissue-Specific Effects of the DNA Helicase FANCJ/BRIP1/BACH1 on Repeat Expansion in a Mouse Model of the Fragile X-Related Disorders

Fragile X-related disorders (FXDs) are caused by the expansion of a CGG repeat tract in the 5'-UTR of the <i>FMR1</i> gene. The expansion mechanism is likely shared with the 45+ other human diseases resulting from repeat expansion, a process that has been shown to require key mismatch repair (MMR) factors. FANCJ, a DNA helicase involved in unwinding unusual DNA secondary structures, has been implicated in a number of DNA repair processes including MMR. To test the role of FANCJ in repeat expansion, we crossed <i>FancJ</i>-null mice to an FXD mouse model. We found that loss of FANCJ resulted in a trend towards more extensive expansion that was significant for the small intestine and male germline. This finding has interesting implications for the expansion mechanism and raises the possibility that other DNA helicases may be important modifiers of expansion risk in certain cell types.