sentence: To test whether the 31aa C-ter tail modulates dystrophin activity , we compared the efficiency of two micro-dystrophin ( μ Dys ) constructs containing either a 13aa tail ( control micro-dystrophin μ Dys-CTL , due to the inclusion of exon 78 ) or a 31aa tail ( μ Dys - Δ 78 due to the lack of exon 78 ) in restoring muscle function of dystrophin-deficient ( mdx ) mice .