From an emedicine article:
Incidence of hypoplastic left heart syndrome is 0.16-0.36 per 1000 live births.16 It comprises 1.2-1.5% of all congenital heart defects.17,18 Hypoplastic left heart syndrome accounts for 7-9% of all congenital heart disease diagnosed in the first year of life.12
- The exact cause of hypoplastic left heart syndrome is unknown. Although familial cases with autosomal recessive inheritance have been reported,6 hypoplastic left heart syndrome is generally postulated to follow multifactorial mode of inheritance.20
- Most likely, the primary abnormality occurs during aortic and mitral valve development. During cardiac development, adequate flow of blood through a structure is largely responsible for the growth of that structure. With little or no blood flow because of aortic and mitral valve atresia, growth of the left ventricle does not occur.
- Similarly, growth of the ascending aorta does not occur because of lack of left ventricular output. The ascending aorta is perfused in retrograde manner from the ductus arteriosus functioning only as a common coronary artery.
- Premature closure or absence of the foramen ovale represents another theoretical cause of hypoplastic left heart syndrome because it eliminates fetal blood flow from the inferior vena cava to the left atrium.21 Fetal pulmonary blood flow is not sufficient for normal development of the left atrium, left ventricle, and ascending aorta.
- Another postulated cause is misalignment of the atrial septum to the left.22
- Recent studies suggest that hypoplastic left heart syndrome is genetically heterogeneous and hypoplastic left heart syndrome and bicuspid aortic valve are genetically related.23,24
So, you know as much as I know about frequency and cause now. Statistically HLHS seems to occur so infrequently, but to me it seems quite the opposite. We know SO MANY families who have a child with HLHS. I don't know if it really is more common than these statistics show or if we all just seek each other out. :) As I've mentioned before, God has a perfect and wonderful plan for Julianne and for our family. We are so thankful that He's given the medical world the wisdom and knowledge to make the advances needed to give HLHS babies a chance at living life and for the skills He's given our wonderful surgeons, doctors and nurses!
Then, I couldn't resist posting some pictures of our little cutie: