Natural History Study in Pediatric Patients With MYBPC3 Mutation-associated Cardiomyopathy

Retrospective Inclusion Criteria: * Data is available for patient \<18 years of age. Patients must be \<18 years of age at enrollment or at time of death. * Documented results of genotyping showing the presence of at least one pathogenic or likely pathogenic MYBPC3 mutation (heterozygous, homozygous, or compound heterozygous). Exclusion Criteria: * Patient received cardiac transplantation or died \>10 years before study initiation. For homozygous or biallelic infants, data may be collected beyond this 10-year period. Prospective Inclusion Criteria: For Infants: * Infants who are homozygous or compound heterozygous for the known pathogenic truncating MYBPC3 mutations are eligible. For all other participants: * Age \<18 at entry into the prospective study. * Documented results of genotyping identifying at least one pathogenic or likely pathogenic MYBPC3 mutation (heterozygous, homozygous, or compound heterozygous). * Diagnosis of Cardiomyopathy (CM): HCM, DCM, RCM, mixed CM, or LVNC. Exclusion Criteria: * Concurrent participation in an interventional clinical trial unless approved by the sponsor. * Severe noncardiac disease anticipated to significantly reduce life expectancy.