MYH6 and hypoplastic left heart syndrome: Next, rare variant burden testing of 56 known cardiomyopathy genes demonstrated enrichment in MYH6 in 23 HLHS probands, 12 of whom had either a MYH6 variant co-segregating with familial CHD, compound heterozygosity, or synergistic heterozygosity with FLNC, which is also a cardiomyopathy gene.