In addition, for patients with DCM, adding thyroid hormone did not appear to influence the left ventricular mass index (LVMI) (WMD: −16.15; 95% CI: −41.41 to 9.12; P > 0.05; AMSTAR 9; Evidence classification IV; Figure 5) and thyroid function compared with the control group (Chen et al., 2022). This evidence concerns the gene TG and familial dilated cardiomyopathy.