Protein restoration as measured by immunohistochemical staining is consistently higher than protein restoration 4 calculated by western blot analysis. These differences may be attributed to the differing "housing proteins" used i.e., dystrophin restoration quantified by immunohistochemical staining is normalized against laminin, whereas western blot analysis uses α-actinin for normalisation. Quantification of western blots has only recently been reported for dystrophin and currently uses chemiluminescence methods. It may therefore be judicious to give greater weight to the trends in dystrophin protein levels revealed by western blot rather than to the absolute values. Therefore, considering the results overall, mdx mice treated with each of the four 5-aa core Pip6-PMOs (Pip6a-, Pip6b-, Pip6e-, and Pip6f-PMO) appear to demonstrate improved dystrophin production and exon skipping in TA, quadriceps, and heart muscles compared with the previous lead candidate, Pip5e-PMO. In addition, these 5-aa core Pip6-PMOs do not exhibit evidence of toxicity, as assessed by plasma levels of relevant toxicity biomarkers, alanine aminotransferase, aspartate aminotransferase, and creatine kinase (see Supplementary Figure S5a ). Blood urea nitrogen and creatinine levels were similar to untreated mdx levels (see Supplementary Figure S5b ). All Pip6-PMO treatment groups exhibit similar biomarker levels to untreated C57BL10 controls.