Examples include the gene titin (ttn.2), which has been causally linked to familial dilated cardiomyopathy in the zebrafish pickwick (pik) mutant [200,201,202]; the zebrafish jekyll (jek) mutant with a loss-of-function mutation in the ugdh gene, which causally linked UDP-glucose 6-dehydrogenase to defective AV valve formation [203,204]; and the zebrafish mutant gridlock (grl), featuring a loss-of-function in the gene hey2, which has been causally linked to defects analogous to human aortic coarctation [205]. The gene discussed is HEY2; the disease is dilated cardiomyopathy.