Hypoplastic left heart syndrome (HLHS) is a clinically and anatomically severe form of congenital heart disease (CHD). Although prior studies suggest that HLHS has a complex genetic inheritance, its etiology remains largely unknown. The goal of this study was to characterize a risk gene in HLHS and its effect on HLHS etiology and outcome. We performed next-generation sequencing on a multigenerational family with a high prevalence of CHD/HLHS, identifying a rare variant in the α-myosin heavy chain (MYH6) gene. A case-control study of 190 unrelated HLHS subjects was then performed and compared with the 1000 Genomes Project. Damaging MYH6 variants, including novel, missense, in-frame deletion, premature stop, de novo, and compound heterozygous variants, were significantly enriched in HLHS cases (P < 1 × 10−5). Clinical outcomes analysis showed reduced transplant-free survival in HLHS subjects with damaging MYH6 variants (P < 1 × 10−2). Transcriptome and protein expression analyses with cardiac tissue revealed differential expression of cardiac contractility genes, notably upregulation of the β-myosin heavy chain (MYH7) gene in subjects with MYH6 variants (P < 1 × 10−3). We subsequently used patient-specific induced pluripotent stem cells (iPSCs) to model HLHS in vitro. Early stages of in vitro cardiomyogenesis in iPSCs derived from two unrelated HLHS families mimicked the increased expression of MYH7 observed in vivo (P < 1 × 10−2), while revealing defective cardiomyogenic differentiation. Rare, damaging variants in MYH6 are enriched in HLHS, affect molecular expression of contractility genes, and are predictive of poor outcome. These findings indicate that the etiology of MYH6-associated HLHS can be informed using iPSCs and suggest utility in future clinical applications.

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Carpenter syndrome is a rare autosomal recessive disorder that belongs to a group of rare craniosynostosis syndromes (Bull Soc Med Paris 1906;23:1310). Carpenter syndrome is the rarest, with only occasional patients seen. There are 3 common features in all of these syndromes: craniosynostosis (skull base abnormalities, with early fusion in different sutures), midface hypoplasia, and musculoskeletal abnormalities. Clinical features of Carpenter syndrome include peculiar facies, asymmetry of the skull, polydactyly, brachymesophalangy, mild soft tissue syndactyly, obesity, hypogenitalism, congenital heart disease, and mental retardation (J Pediatr 1966;69:1; Am J Roentgenol 1969;106). The brachycephaly is caused by early fusion in the coronal, sagittal, and lambdoidal sutures (Proc R Soc Med Sect Study Dis Child 1909). Most of the affected patients have a surgical procedure between 3 to 9 months of age to open the cranial vault to make space for the brain to grow (Plast Reconstr Surg 1978;62:335). We present a patient with Carpenter syndrome who is unusual in that she is an adult who has never had surgical intervention.

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