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). This evidence concerns the gene MYL2 and cutaneous mastocytosis.