(1) 22 mice with six different genetic backgrounds (CASK KO and control, SAP97 KO and control, and MDX and control) were used. fl+, first exon of gene is floxed; Cre+, Cre recombinase is expressed. (2) Cardiomyocytes were isolated on a Langendorff system and RNA was isolated with a FFPE Clear RNAready kit. (3) Libraries were constructed with 1 μg RNA per sample using a TrueSeq Stranded Total RNA protocol and (4) sequenced on an Illumina HiSeq3000 machine. (5) Quality of the reads was assessed with FastQC, and (6) reads were mapped to the Mus musculus reference genome (GRCm38.83) with Tophat. (7) To assess sample variation within each group, we performed principle component analyses (PCA) (see Fig. 3). (8) Lastly, ion channel expression was determined.