HLHS is caused by the up regulation of HIF1α due to hypoxia caused by a polymorphism in eNOS

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect occurring in fewer than 0.5% of live births in the United States (Fruitman, 2000). It is characterized by a critically underdeveloped left ventricle with accompanying imperfections including septal defects, under-sized aorta, and underdeveloped bicuspid and aortic semilunar valves (Mayo Clinic Staff, 2012; CDC, 2013). HLHS is detectable on ultrasound at the end of the first trimester of pregnancy allowing for early diagnosis and potential treatment in utero. While a protocol involving three surgeries exists to treat the condition, there is no cure for HLHS. Even with treatment, many patients eventually require a heart transplant due to congestive heart failure