Congenital heart defects (CHDs) are etiologically heterogeneous, but in recent years it has become clear that genetics plays a larger role in the development of CHDs than was previously thought. Research has been shifting from a focus on risk – estimating the magnitude of increased risk, for instance, based on maternal or familial risk factors – to a focus on the etiology of cardiac defects.
In practice, advances in genetic testing technologies have made the underlying causes of CHDs increasingly detectable. Chromosomal microarray analysis (CMA) – technology that detects significantly more and smaller changes in the amount of chromosomal material than traditional karyotype – has been proven to increase the diagnostic yield in cases of isolated CHDs and CHDs with extracardiac anomalies. Targeted next-generation sequencing also is now available as an additional approach in selective cases, and a clinically viable option for whole-exome sequencing is fast approaching.
For researchers, genetic evaluation carries the potential to unravel remaining mysteries about underlying causes of CHDs – to provide pathological insights and identify potential therapeutic targets. Currently, about 6 % of the total pie of presumed genetic determinants of CHDs is attributed to chromosomal anomalies, 10% to copy number variants, and 12% to single-gene defects. The remaining 72% of etiology, approximately, is undetermined.
As Helen Taussig, MD, (known as the founder of pediatric cardiology) once said, common cardiac malformations occurring in otherwise “normal” individuals “must be genetic in origin.”1 Greater use of genetic testing – and in particular, of whole-exome sequencing – will drive down this “undetermined” piece of the genetics pie.
For clinicians and patients, prenatal genetic evaluation can inform clinical management, guiding decisions on the mode, timing, and location of delivery. Genetic assessments help guide the neonatal health care team in taking optimal care of the infant, and the surgeon in preparing for neonatal surgeries and postsurgical complications.
In a recent analysis of the Society of Thoracic Surgeons Congenital Heart Surgery Database, prenatal diagnosis was associated with a lower overall prevalence of major preoperative risk factors for cardiac surgery.2 Surgical outcomes themselves also have been shown to be better after the prenatal diagnosis of complex CHDs, mainly because of improvements in perioperative care.3
When genetic etiology is elucidated, the cardiologist also is better able to counsel patients about anticipated challenges – such as the propensity, with certain genetic variants of CHD, to develop neurodevelopmental delays or other cardiac complications – and to target patient follow-up. Patients also can make informed decisions about termination or continuation of a current pregnancy and about family planning in the future.
Fortunately, advances in genetics technology have paralleled technological advancements in ultrasound. As I discussed in part one of this two-part Master Class series, it is now possible to detect many major CHDs well before 16 weeks’ gestation. Checking the structure of the fetal heart at the first-trimester screening and sonography (11-14 weeks of gestation) offers the opportunity for early genetic assessment, counseling, and planning when anomalies are detected.