MYL3 and cutaneous mastocytosis: Biallelic PTVs in MYBPC3, TNNI3, MYL2 and MYL3 are associated with severe, early-onset CM phenotypes, which can include additional features such as atrial and ventricular septal defects and skeletal myopathy (Fig. 4a,b, Extended Data Fig. 3a and Supplementary Table 5).