To mimic the cardiomyopathy and CCD caused by this human TNNI3K variant, we designed a single guide RNA targeting the splicing donor site of the 4th exon in the zebrafish tnni3k gene and generated a splicing mutant in the predicted splice donor site via CRISPR/Cas9 technology (Fig. 1B; Fig. S2A–C). The gene discussed is TNNI3K; the disease is cardiomyopathy.