The chromosomal abnormalities that cause Turner syndrome have far-reaching effects across multiple body systems. One of the more prevalent effects of TS can be found in the heart, as congenital heart defects are present in 23-50% of all individuals with TS (Silberbach et al., 2018).
The exact cause of these congenital defects remains unclear, but it is known that patients with the 45X karyotype are affected at a higher rate than individuals with a mosaic or other karyotype (Gravholt, 2002). The SHOX gene, discussed in this post on Knock Knees, has also been identified as contributing to reduced growth of certain structures that may lead to cardiovascular issues.
Find more information about TS and heart health here. If you or someone you know has TS and has experienced a heart condition related to TS as a newborn or infant, tell us about your experience here.
A recent story about a young TS patient with Hypoplastic Left Heart Syndrome (HLHS) has brought attention to this specific congenital heart defect in relation to Turner syndrome.
What is Hypoplastic Left Heart Syndrome?
It is important to note that HLHS is extremely rare, constituting 1.6-3.6 out of 1000 live births, and making up less than 3% of all congenital heart defects (Kritzmire et al., 2025). However, up to 20% of HLHS cases are associated with chromosomal abnormalities such as Trisomy 13, Trisomy 18, or TS.
For individuals with TS, HLHS is far less frequent than other cardiac abnormalities such as BAV, aortic coarctation, and coronary artery abnormalities (Silberbatch et al., 2018).
HLHS is characterized by the underdevelopment of left-sided cardiac structures including the left ventricle, mitral valve, aortic valve, and ascending aorta (Kritzmire et al., 2025).
The main cause of this condition is obstruction of left ventricle outflow during fetal development, which increases load on the left ventricle, impairing its growth. This also diminished blood flow to the ascending aorta and aortic arch, inhibiting their development (Kritzmire et al., 2018).
How is HLHS diagnosed?
Babies with HLHS are often born slightly premature, between 37-38 weeks of gestation. Initial physical findings of cyanosis (bluish tone in extremities from lack of oxygen), tachypnea, and oxygen saturations less than 95% prompt an echocardiogram for further evaluation (Kritzmire et al., 2018).
Laboratory tests may also be used to evaluate metabolic stability. An arterial blood gas test can be used to determine blood oxygenation, ventilation, and acid-base balance. If HLHS is detected via echocardiogram, genetic testing is performed, as individuals with chromosomal syndromes such as TS, DiGeorge, or Down syndrome have higher morbidity and mortality rates, as well as longer hospital stays (Kritzmire et al., 2018). This is likely due to additional cardiac or other structural issues caused by the genetic abnormalities.
How is HLHS treated?
The first step in HLHS treatment is postnatal management, where infants are stabilized in the ICU before surgical intervention. This treatment can include intravenous prostaglandin E1 to maintain ductal patency, supplementary oxygen, and minor surgery to relieve obstruction to left arterial flow (Kritzmire et al., 2018).
Following stabilization, HLHS treatment has 3 stages of surgical management.
Stage 1
This stage occurs immediately after birth, and 3 options are currently available.
Option 1: The Norwood procedure sets up the heart to function with the right ventricle only, bypassing the underdeveloped left ventricle. In this procedure, the aortic arch is reconstructed, the atrial septum is removed, a neoaorta is created, and a BT shunt is added to allow blood to flow to the lungs (Kritzmire et al., 2018).
Option 2: The Sano Procedure is a modification of the Norwood procedure that uses a nonvalved Sano shunt instead of a BT shunt to allow blood flow between the right ventricle and pulmonary artery (Kritzmire et al., 2018).
This procedure, when compared to the conventional Norwood procedure, has the advantage of providing diastolic pressure closer to normal levels, as well as improved pulmonary perfusion (blood flow through the lungs). However, it increases the risk of right ventricular arrhythmia or impairment (Kritzmire et al., 2018).
In the short term, the Sano procedure has greater transplant-free survival at 1 year than the Norwood procedure, although this advantage disappears by 6 years (Kritzmire et al., 2018).
Option 3: The hybrid procedure is an alternative to the Norwood procedure for neonates who are high risk surgical candidates–premature, low birth weight, or significant comorbidities (Kritzmire et al., 2018).
This procedure minimizes physiologic stress by avoiding cardiopulmonary bypass during surgery, which is when blood flow is diverted away from the heart and lungs to allow surgeons to work on these organs. Instead, the procedure uses cardiac catheterization and an off-pump cardiopulmonary bypass, where the surgeons can operate on the heart while it is beating by using mechanical stabilization (Kritzmire et al., 2018).
Stage 2
This stage occurs within 6 months of birth, following the Stage 1 procedure.
A Hemi-fontan or bidirectional glen procedure is used to connect the superior vena cava to the pulmonary artery. This allows deoxygenated blood from the upper body to go directly to the lungs to receive oxygen, without passing through the heart (Philadelphia, n.d.).
Stage 3
This stage occurs at 1.5-3 years of age.
Here, the Fontan procedure is used to connect the inferior vena cava to the pulmonary artery, so now deoxygenated blood from the lower body also goes directly to the lungs without passing through the heart (Philadelphia, n.d.).
Conclusion
HLHS is more prevalent in individuals with chromosomal abnormalities such as TS, but is not an exceptionally common condition for individuals with TS.
All individuals with TS should be evaluated by a cardiologist for all potential heart issues as recommended by the AHA. Before birth, a fetal echocardiogram can be used to diagnose potential congenital heart defects. After birth or for newly diagnosed patients, a physical examination should be performed, along with a complete TTE (ultrasound of the heart), visualization of the coronary artery (via TTE, cardiac MRI, or CT), and an echocardiogram.
Should an abnormality be detected, a cardiologist, assisted by a multidisciplinary team, will be able to determine the best course of action and provide all treatment options available.
References
Gravholt, C. H. (2002). Turner Syndrome and the heart. American Journal of Cardiovascular Drugs, 2(6), 401–413. https://doi.org/10.2165/00129784-200202060-00005
Hypoplastic Left Heart Syndrome (HLHS). (2026, April 23). Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/12214-hypoplastic-left-heart-syndrome-hlhs
Kritzmire, S. M., Thomas, A., Horenstein, M. S., & Cossu, A. E. (2025, January 19). Hypoplastic left heart syndrome. StatPearls – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK554576/
Philadelphia, C. H. O. (n.d.). Staged Reconstruction heart Surgery | Children’s Hospital of Philadelphia. Children’s Hospital of Philadelphia. https://www.chop.edu/treatments/staged-reconstruction-heart-surgery
Silberbach, M., Roos-Hesselink, J. W., Andersen, N. H., Braverman, A. C., Brown, N., Collins, R. T., De Backer, J., Eagle, K. A., Hiratzka, L. F., Johnson, W. H., Kadian-Dodov, D., Lopez, L., Mortensen, K. H., Prakash, S. K., Ratchford, E. V., Saidi, A., Van Hagen, I., & Young, L. T. (2018). Cardiovascular health in Turner Syndrome: A scientific statement from the American Heart Association. Circulation Genomic and Precision Medicine, 11(10), e000048. https://doi.org/10.1161/hcg.0000000000000048
Written By Nadia Kim, TSF Volunteer Blog Writer and designed by Adrianna Verzolini
© Turner Syndrome Foundation, 2026
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