The Current Landscape of Genetic Testing in Cardiovascular Malformations: Opportunities and Challenges

Human cardiovascular malformations (CVMs) frequently have a genetic contribution. Through the application of novel technologies, such as next-generation sequencing, DNA sequence variants associated with CVMs are being identified at a rapid pace. While clinicians are now able to offer testing with NGS gene panels or whole exome sequencing to any patient with a CVM, the interpretation of genetic variation remains problematic. Variable phenotypic expression, reduced penetrance, inconsistent phenotyping methods, and the lack of high-throughput functional testing of variants contribute to these challenges. This article elaborates critical issues that impact the decision to broadly implement clinical molecular genetic testing in CVMs. Major benefits of testing include establishing a genetic diagnosis, facilitating cost-effective screening of family members who may have subclinical disease, predicting recurrence risk in offsprings, enabling early diagnosis and anticipatory management of CV and non-CV disease phenotypes, predicting long-term outcomes, and facilitating the development of novel therapies aimed at disease improvement or prevention. Limitations include financial cost, psychosocial cost, and ambiguity of interpretation of results. Multiplex families and patients with syndromic features are two groups where disease causation could potentially be firmly established. However, these account for the minority of the overall CVM population, and there is increasing recognition that genotypes previously associated with syndromes also exist in patients who lack non-CV findings. In all circumstances, ongoing dialog between cardiologists and clinical geneticists will be needed to accurately interpret genetic testing and improve these patients' health. This may be most effectively implemented by the creation and support of CV genetics services at centers committed to pursuing testing for patients

Bicuspid Aortic Valve: a Review with Recommendations for Genetic Counseling

Bicuspid aortic valve (BAV) is the most common congenital heart defect and falls in the spectrum of left-sided heart defects, also known as left ventricular outflow tract obstructive (LVOTO) defects. BAV is often identified in otherwise healthy, asymptomatic individuals, but it is associated with serious long term health risks including progressive aortic valve disease (stenosis or regurgitation) and thoracic aortic aneurysm and dissection. BAV and other LVOTO defects have high heritability. Although recommendations for cardiac screening of BAV in at-risk relatives exist, there are no standard guidelines for providing genetic counseling to patients and families with BAV. This review describes current knowledge of BAV and associated aortopathy and provides guidance to genetic counselors involved in the care of patients and families with these malformations. The heritability of BAV and recommendations for screening are highlighted. While this review focuses specifically on BAV, the principles are applicable to counseling needs for other LVOTO defects

CHD associated with syndromic diagnoses: peri-operative risk factors and early outcomes

CHD is frequently associated with a genetic syndrome. These syndromes often present specific cardiovascular and non-cardiovascular co-morbidities that confer significant peri-operative risks affecting multiple organ systems. Although surgical outcomes have improved over time, these co-morbidities continue to contribute substantially to poor peri-operative mortality and morbidity outcomes. Peri-operative morbidity may have long-standing ramifications on neurodevelopment and overall health. Recognising the cardiovascular and non-cardiovascular risks associated with specific syndromic diagnoses will facilitate expectant management, early detection of clinical problems, and improved outcomes--for example, the development of syndrome-based protocols for peri-operative evaluation and prophylactic actions may improve outcomes for the more frequently encountered syndromes such as 22q11 deletion syndrome

Genetic Evaluation of Inpatient Neonatal and Infantile Congenital Heart Defects: New Findings and Review of the Literature

The use of clinical genetics evaluations and testing for infants with congenital heart defects (CHDs) is subject to practice variation. This single-institution cross-sectional study of all inpatient infants with severe CHDs evaluated 440 patients using a cardiovascular genetics service (2014-2019). In total, 376 (85.5%) had chromosome microarray (CMA), of which 55 (14.6%) were diagnostic in syndromic (N = 35) or isolated (N = 20) presentations. Genetic diagnoses were made in all CHD classes. Diagnostic yield was higher in syndromic appearing infants, but geneticists' dysmorphology exams lacked complete sensitivity and 6.5% of isolated CHD cases had diagnostic CMA. Interestingly, diagnostic results (15.8%) in left ventricular outflow tract obstruction (LVOTO) defects occurred most often in patients with isolated CHD. Geneticists' evaluations were particularly important for second-tier molecular testing (10.5% test-specific yield), bringing the overall genetic testing yield to 17%. We assess these results in the context of previous studies. Cumulative evidence provides a rationale for comprehensive, standardized genetic evaluation in infants with severe CHDs regardless of lesion or extracardiac anomalies because genetic diagnoses that impact care are easily missed. These findings support routine CMA testing in infants with severe CHDs and underscore the importance of copy-number analysis with newer testing strategies such as exome and genome sequencing

Clinically relevant variants identified in thoracic aortic aneurysm patients by research exome sequencing

Thoracic aortic aneurysm (TAA) is a genetically heterogeneous disease involving subclinical and progressive dilation of the thoracic aorta, which can lead to life-threatening complications such as dissection or rupture. Genetic testing is important for risk stratification and identification of at risk family members, and clinically available genetic testing panels have been expanding rapidly. However, when past testing results are normal, there is little evidence to guide decision-making about the indications and timing to pursue additional clinical genetic testing. Results from research based genetic testing can help inform this process. Here we present 10 TAA patients who have a family history of disease and who enrolled in research-based exome testing. Nine of these ten patients had previous clinical genetic testing that did not identify the cause of disease. We sought to determine the number of rare variants in 23 known TAA associated genes identified by research-based exome testing. In total, we found 10 rare variants in six patients. Likely pathogenic variants included a TGFB2 variant in one patient and a SMAD3 variant in another. These variants have been reported previously in individuals with similar phenotypes. Variants of uncertain significance of particular interest included novel variants in MYLK and MFAP5, which were identified in a third patient. In total, clinically reportable rare variants were found in 6/10 (60%) patients, with at least 2/10 (20%) patients having likely pathogenic variants identified. These data indicate that consideration of re-testing is important in TAA patients with previous negative or inconclusive results

Early aberrant angiogenesis due to elastic fiber fragmentation in aortic valve disease

Elastic fiber fragmentation (EFF) is a hallmark of aortic valve disease (AVD), and neovascularization has been identified as a late finding related to inflammation. We sought to characterize the relationship between early EFF and aberrant angiogenesis. To examine disease progression, regional anatomy and pathology of aortic valve tissue were assessed using histochemistry, immunohistochemistry, and electron microscopy from early-onset (\u3c40 yo) and late-onset (≥40 yo) non-syndromic AVD specimens. To assess the effects of EFF on early AVD processes, valve tissue from Williams and Marfan syndrome patients was also analyzed. Bicuspid aortic valve was more common in early-onset AVD, and cardiovascular comorbidities were more common in late-onset AVD. Early-onset AVD specimens demonstrated angiogenesis without inflammation or atherosclerosis. A distinct pattern of elastic fiber components surrounded early-onset AVD neovessels, including increased emilin-1 and decreased fibulin-5. Different types of EFF were present in Williams syndrome (WS) and Marfan syndrome (MFS) aortic valves; WS but not MFS aortic valves demonstrated angiogenesis. Aberrant angiogenesis occurs in early-onset AVD in the absence of inflammation, implicating EFF. Elucidation of underlying mechanisms may inform the development of new pharmacologic treatments

Exome Sequencing Identifies Candidate Genetic Modifiers of Syndromic and Familial Thoracic Aortic Aneurysm Severity

Thoracic aortic aneurysm (TAA) is a genetic disease predisposing to aortic dissection. It is important to identify the genetic modifiers controlling penetrance and expressivity to improve clinical prognostication. Exome sequencing was performed in 27 subjects with syndromic or familial TAA presenting with extreme phenotypes (15 with severe TAA; 12 with mild or absent TAA). Family-based analysis of a subset of the cohort identified variants, genes, and pathways segregating with TAA severity among three families. A rare missense variant in ADCK4 (p.Arg63Trp) segregated with mild TAA in each family. Genes and pathways identified in families were further investigated in the entire cohort using the optimal unified sequence kernel association test, finding significance for the gene COL15A1 (p = 0.025) and the retina homeostasis pathway (p = 0.035). Thus, we identified candidate genetic modifiers of TAA severity by exome-based study of extreme phenotypes, which may lead to improved risk stratification and development of new medical therapies

Contrasting sensitivity of lake sediment n-alkanoic acids and n-alkanes to basin-scale vegetation and regional-scale precipitation δ2H in the Adirondack Mountains, NY (USA)

The hydrogen isotope values of plant waxes (δ2Hwax) primarily reflect plant source water. δ2Hwax preserved in lake sediments has therefore been widely used to investigate past hydroclimate. The processes by which plant waxes are integrated at regional and catchment scales are poorly understood and may affect the δ2Hwax values recorded in sediments. Here, we assess the variability of sedimentary δ2Hwax for two plant wax compound classes (n-alkanes and n-alkanoic acids) across 12 lakes in the Adirondack Mountains that receive similar regional precipitation δ2H but vary at the catchment-scale in terms of vegetation structure and basin morphology. Total long-chain (n-C27 to n-C35) alkane concentrations were similar across all sites (191 ± 53 µg/g TOC) while total long-chain (n-C28 and n-C30) alkanoic acid concentrations were more variable (117 ± 116 µg/g TOC) and may reflect shoreline vegetation composition. Lakes with shorelines dominated by evergreen gymnosperm plants had significantly higher concentrations of long-chain n-alkanoic acids relative to n-alkanes, consistent with our observations that deciduous angiosperms produced more long-chain n-alkanes than evergreen gymnosperms (471 and 33 µg/g TOC, respectively). In sediments, the most abundant chain lengths in each compound class were n-C29 alkane and n-C28 alkanoic acid, which had mean δ2H values of −188 ± 6‰ and −164 ± 9‰, respectively. Across sites, the range in sedimentary n-C29 alkane (22‰) and n-C28 alkanoic acid δ2H (35‰) was larger than expected based on the total range in modeled mean annual precipitation δ2H (4‰). We observed larger mean εapp (based on absolute values) for n-alkanes (−123‰) than for n-alkanoic acids (−97‰). Across sites, the δ2H offset between n-C29 alkane and the biosynthetic precursor n-C30 alkanoic acid (εC29-C30) ranged from −8 to −58‰, which was more variable than expected based on observations in temperate trees (−20 to −30‰). Sediments with greater aquatic organic matter contributions (lower C/N ratios) had significantly larger (absolute) εC29-C30 values, which may reflect long-chain n-alkanoic acids from aquatic sources. Concentration and δ2Hwax data in Adirondack lakes suggest that long-chain n-alkanes are more sensitive to regional-scale precipitation signals, while n-alkanoic acids are more sensitive to basin-scale differences in catchment vegetation and wax sourcing