Statistical analysis
The statistical analysis was performed with Medcalc statistical software (Medcalc, Ostend, Belgium). The significance level was set at 0.05. We analyzed correlations using Spearman’s coefficient at three different levels: patients; myoblast pools and single myoblasts. We used this test for correlating patients’ clinical data (age at onset, mRS, MIRS, biceps MRC and 6MWT) and: foci mean, foci median and percentage of cells with foci, DMPK and MBNL1 expression means and muscle CTG expansion size. We also studied correlations using Spearman’s coefficient in myoblast pools: between mean, median and percentage of cells with foci and expansion size in myoblasts, between DMPK andMBNL1 expression and expansion size in myoblasts, between expansion size in myoblasts pools and expansion size in muscle tissue in patients. At single cell level, we studied the correlation between RNA foci number and DMPK and MBNL1 expression. The Mann Whitney-U test was used to compare DMPK and MBNL1exon 7 exclusion expression between controls and DM1 patients. The Kruskal-Wallis test for inter-individual comparisons of DMPK andMBNL1 exon 7 exclusion expression, both in patients and in controls.