Hypoplastic left heart syndrome
| Hypoplastic left heart syndrome | |
|---|---|
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| Illustration of heart suffering from Hypoplastic left heart syndrome | |
| Classification and external resources | |
| Specialty | cardiology |
| ICD-10 | Q23.4 |
| ICD-9-CM | 746.7 |
| OMIM | 241550 |
| DiseasesDB | 31507 |
| MedlinePlus | 001106 |
| eMedicine | ped/1131 |
| MeSH | C14.240.400.625 |
Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect in which the left heart is severely underdeveloped. The International Working Group for Mapping and Coding of Nomenclatures for Paediatric and Congenital Heart Disease defined HLHS as
... a spectrum of cardiac malformations with normally aligned great arteries without a common atrioventricular junction, characterized by underdevelopment of the left heart with significant hypoplasia of the left ventricle including atresia, stenosis, or hypoplasia of the aortic or mitral valve, or both valves, and hypoplasia of the ascending aorta and aortic arch.
In typical anatomy, the left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body. In people with HLHS, the aorta and left ventricle are underdeveloped (beginning in utero), and the aortic and mitral valves are either too small to allow sufficient blood flow or are atretic (closed) altogether. As blood returns from the lungs to the left atrium, it must pass through an atrial septal defect to the right side of the heart so it can be pumped to the rest of the body. This blood must flow through a patent (open) ductus arteriosus. Since the ductus arteriosus usually closes within eleven days after birth, blood flow may be severely restricted and eventually blocked, leading to dangerously low circulation and, eventually, shock. Babies are often cyanotic at birth to varying degrees, depending on the severity of their defects.
There is no known cause in the majority of HLHS cases. There is likely a genetic component, as HLHS has been shown to be heritable and associated with specific gene mutations.
In a retrospective analysis of over 1,300 newborns (born between 1996 and 2006) from 24 children’s hospitals in the United States, researchers at Cincinnati Children’s Hospital in Ohio found that babies with HLHS were more likely to be born in summer months, suggesting that seasonality and environmental factors play a significant role in causation.
HLHS usually occurs as an isolated cardiac defect. Genetic loci associated with HLHS include GJA1 (connexin 43), HAND1, NKX2.5, 10q, and 6q. There is a slight risk of recurrence in future pregnancies, estimated to be 2-4%, which increases to 25% in families with two affected children. HLHS has been seen in the following genetic syndromes: Trisomy 13 (Patau syndrome), Trisomy 18 (Edwards syndrome), Partial Trisomy 9, Turner's syndrome, Jacobsen syndrome, Holt-Oram Syndrome, and Smith-Lemli-Opitz Syndrome.
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