DISCUSSION Previously, we have identified genetic variants in the NPL gene in two siblings with cardiomyopathy/skeletal muscle myopathy and demonstrated that these variants interfere with NPL protein levels and/or enzymatic activity. We have also demonstrated that npl zebrafish morphants develop muscle and heart phenotypes that are rescued by the induced expression of the WT enzyme, but not by its p.Arg63Cys or p.Asn45Asp variants, establishing association of these mutations with the disease.