CELF1 and myotonic dystrophy type 1: Third, the reduction in hnRNP-A3 mRNA in CUGBP1-KI brain cortices (own unpublished data) suggests that this protein might be reduced in DM1 tissues, since the amounts of inactive CUGBP1, unphosphorylated at S302, are increased in DMSXL mice expressing > 1,000 CTG repeats [18].