Mutations in hydratase subunit A (HADHA) can cause sudden infant death syndrome due to cardiac arrhythmias after initiation of enteral feeds; PSC-CMs with deletion of HADHA have an immature cardiomyocyte phenotype, fragmented mitochondria with accumulation of long-chain fatty acids, and an increase in action potential duration although no change in resting membrane potential [266]. Here, HADHA is linked to chronic obstructive pulmonary disease.