Congenital heart disease: Genetic causes and developmental insights

Rapid quantitative high-throughput mouse embryoid body model for embryotoxicity assessment

Individuals are exposed to a wide arrays of hazardous chemicals on a daily basis through various routes, many of which have not undergone comprehensive toxicity assessments. While traditional developmental toxicity tests involving pregnant animals are known for their reliability, they are also associated with high costs and time requirements. Consequently, there is an urgent demand for alternative, cost-efficient, and rapid in vitro testing methods. This study aims to address the challenges related to automating and streamlining the screening of early developmental toxicity of chemicals by introducing a mouse embryoid body test (EBT) model in a 384-ultra low attachment well format. Embryoid bodies (EBs) generated in this format were characterized by a spontaneous differentiation trajectory into cardiac mesoderm by as analyzed by RNA-seq. Assessing prediction accuracy using reference compounds suggested in the ICH S5(R3) guideline and prior studies resulted in the establishment of the acceptance criteria and applicability domain of the EBT model. The results indicated an 84.38% accuracy in predicting the developmental toxicity of 23 positive and 9 negative reference compounds, with an optimized cutoff threshold of 750 µM. Overall, the developed EBT model presents a promising approach for more rapid, high-throughput chemical screening, thereby facilitating well-informed decision-making in environmental management and safety assessments.

Human Genetics of Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a severe congenital cardiovascular malformation characterized by hypoplasia of the left ventricle, aorta, and other structures on the left side of the heart. The pathologic definition includes atresia or stenosis of both the aortic and mitral valves. Despite considerable progress in clinical and surgical management of HLHS, mortality and morbidity remain concerns. One barrier to progress in HLHS management is poor understanding of its cause. Several lines of evidence point to genetic origins of HLHS. First, some HLHS cases have been associated with cytogenetic abnormalities (e.g., Turner syndrome). Second, studies of family clustering of HLHS and related cardiovascular malformations have determined HLHS is heritable. Third, genomic regions that encode genes influencing the inheritance of HLHS have been identified. Taken together, these diverse studies provide strong evidence for genetic origins of HLHS and related cardiac phenotypes. However, using simple Mendelian inheritance models, identification of single genetic variants that "cause" HLHS has remained elusive, and in most cases, the genetic cause remains unknown. These results suggest that HLHS inheritance is complex rather than simple. The implication of this conclusion is that researchers must move beyond the expectation that a single disease-causing variant can be found. Utilization of complex models to analyze high-throughput genetic data requires careful consideration of study design.

A case of 46,XY disorders of sex development with congenital heart disease caused by a GATA4 variant

GATA4 is known to be a causative gene for congenital heart disease, but has also now been associated with disorders of sexual development (DSD). We here report a pathogenic variant of GATA4 in a 46,XY DSD patient with an atrial septal defect, identified by whole-exome sequencing to be c.487C>T (p.Pro163Ser). This mutation resulted in reduced transcriptional activity of the downstream gene. When we compared this transcriptional activity level with other GATA4 variants, those that had been identified in patients with cardiac defects and DSD showed less activity than those in patients with cardiac defect only. This suggests that the normal development of the heart requires more strict regulation of GATA4 transcription than testicular development. Further, when the different variants were co-expressed with wild-type, the transcriptional activities were consistently lower than would be expected from an additive effect, suggesting a dominant-negative impact of the variant via dimer formation of the GATA4 protein. Since these pathogenic GATA4 variants are occasionally identified in healthy parents, a threshold model of quantitative traits may explain the cardiac defect or DSD phenotypes that they cause.

Understanding Genetics and Pediatric Cardiac Health

Congenital heart defects (CHD) continue to be the most prevalent birth defect that occurs worldwide in approximately 6-8 of every 1,000 live births. High rates of morbidity and mortality in infants, children, and adults living with CHD place a growing need for health care professionals (HCPs) to better understand potentially modifiable genetic and environmental influences. This paper will present examples of research and governmental initiatives that support genetics education and research and a review of known genetic factors associated with CHD development.

ORGANIZING CONSTRUCT

A review of the known genetic factors on risk for CHD formation in infants will be provided to help health care professionals gain a greater understanding of the genetic influences on pediatric cardiac health.

CONCLUSIONS

There are known genetic pathways and risk factors that contribute to development of CHD. This paper is a primer for nurses and HCPs providing information of the genetics and inheritance patterns of CHD to be useful in daily clinical practice.

CLINICAL RELEVANCE

Nurses work in multiple communities where they are uniquely positioned to educate and provide information about research and current models of care with families affected by CHD. Nurses and HCPs who better understand genetic risk factors associated with CHD development can more promptly refer and offer treatment for these children and families thus providing individuals of childbearing age with the necessary resources and information about risk factors.

Analyses of GATA4, NKX2.5, and TFAP2B genes in subjects from southern China with sporadic congenital heart disease

BACKGROUND

Congenital heart disease is the most common birth defect in newborns in southern China. The germline mutations in GATA4, NKX2.5, and TFAP2B genes have been identified to be responsible for congenital heart disease. The frequency of GATA4, NKX2.5, and TFAP2B mutations in subjects with congenital heart disease in southern China and the correlation between their genotype and congenital heart disease phenotype are not known.

METHODS

We screened germline mutations in the coding exons and the flanking intron sequences of the GATA4, NKX2.5, and TFAP2B genes in 224 congenital heart disease patients located in southern China by denaturing high-performance liquid chromatography and DNA sequencing.

RESULTS

Fifteen heterozygous mutations in the GATA4 gene were identified in 30 congenital heart disease patients, including a novel heterozygous missense mutation (c.788 C>G) of GATA4 in one patient with ventricular septal defect. A novel TFAP2B mutation (c.31 A>G) in a patient with endocardial cushion defect and an unreported novel TFAP2B variant (c.1006 G>A) in six patients suffering from tetralogy of Fallot (one patient), persistent truncus arteriosus (two patients) and patent ductus arteriosus (three patients) was found. There were no reported NKX2.5 mutations except for several single nucleotide polymorphisms in the patients.

CONCLUSION

These results suggest that genomic GATA4 and TFAP2B missense mutations may be associated with nonfamilial congenital heart disease with diverse clinical phenotypes in patients with congenital heart disease from southern China. They also revealed that the variation of the NKX2.5 gene may not be a risk factor for sporadic patients with congenital heart disease in this population.

Hypoplastic left heart syndrome links to chromosomes 10q and 6q and is genetically related to bicuspid aortic valve

OBJECTIVES

This study was designed to identify disease loci for hypoplastic left heart syndrome (HLHS) and evaluate the genetic relationship between HLHS and bicuspid aortic valve (BAV).

BACKGROUND

Previously, we identified that HLHS and BAV exhibit complex inheritance, and both HLHS and BAV kindreds are enriched for BAV. However, the genetic basis of HLHS and its relationship to BAV remains unclear.

METHODS

Family-based nonparametric genome-wide linkage analysis was performed in kindreds ascertained by either an HLHS or BAV proband. Echocardiograms were performed on 1,013 participants using a sequential sampling strategy (33 HLHS kindreds, 102 BAV kindreds).

RESULTS

The recurrence risk ratio of BAV in HLHS families (8.05) was nearly identical to that in BAV families (8.77). Linkage to chromosomal regions 10q22 and 6q23 with maximum logarithm of odds scores of 3.2 and 3.1, respectively, was identified in HLHS kindreds. In addition, 5 suggestive loci were identified (7q31, 11q22, 12q13, 14q23, and 20q11). We previously identified loci at chromosomes 18q22, 13q34, and 5q21 in BAV kindreds. The relationship between these loci was examined in the combined HLHS and BAV cohort and associations between loci were demonstrated (5q21, 13q34, and 14q23; 6q23 and 10q22; 7q31 and 20q11). Subsequent subsets linkage analysis showed a significant improvement in the logarithm of odds score at 14q23 only (4.1, p < 0.0001).

CONCLUSIONS

These studies demonstrate linkage to multiple loci identifying HLHS as genetically heterogeneous. Subsets linkage analyses and recurrence risk ratios in a combined cohort provide evidence that some HLHS and BAV are genetically related.

The family history: reemergence of an established tool

Genetics has transformed the use of family history information and has led to the reemergence of the detailed genetic family history. It is critical that public and professional educational efforts to increase family history awareness and working knowledge are prioritized. Patient maintenance of the pedigree provides increased patient awareness and facilitates some of the limitations associated with conventional medical history ascertainment, ultimately improving health care and research. The increasing use of genetic screening promises to cultivate a paradigm shift in medical treatment emphasizing primary prevention and early intervention. Appreciation of the family history is necessary to make this important advance.

Mouse heart valve structure and function: echocardiographic and morphometric analyses from the fetus through the aged adult

The purpose of this study is to provide standard echocardiographic and morphometric data for normal mouse valve structure and function from late fetal to aged adult stages. Cross-sectional, two-dimensional and Doppler transthoracic echocardiography was performed in C57BL6 mice anesthetized with 1% to 2% isoflurane at embryonic day 18.5 (late fetal), 10 days (neonate), 1 mo (juvenile), 2 mo (young adult), 9 mo (old adult), and 16 mo (aged adult). Normal annulus dimensions indexed to age or weight, and selected flow velocities, were established by echocardiography. After echocardiographic imaging, hearts were harvested and histological and morphometric analyses were performed. Morphometric analysis demonstrated a progressive valve thinning and elongation during the fetal and juvenile stages that plateaued during adult stages (ANOVA, P < 0.01); however, there was increased thickening of the hinge of the aortic valve with advanced age, reminiscent of human aortic valve sclerosis. There was no age-related calcification. The results of this study provide comprehensive echocardiographic and morphometric data for normal mouse valve structure and function from late fetal to aged adult stages and should prove useful as a reference standard for future studies using mouse models of progressive valve disease.

Hypoplastic left heart syndrome is heritable

OBJECTIVES

This study sought to determine the size of the genetic effect (heritability) in families identified by a hypoplastic left heart syndrome (HLHS) proband.

BACKGROUND

Hypoplastic left heart syndrome is a severe form of cardiovascular malformation (CVM), and it remains a leading cause of infant mortality and childhood morbidity. Familial clustering of HLHS and bicuspid aortic valve (BAV) has been observed, and pedigree analysis has suggested recessive inheritance. The genetic significance of these observations is unknown.

METHODS

In 38 probands with HLHS, a 3-generation family history was obtained; using a sequential sampling strategy, echocardiograms on family members were performed. A total of 235 participants were recruited. Heritability (h2) of HLHS and associated CVM was estimated using maximum-likelihood-based variance decomposition.

RESULTS

All HLHS probands had aortic valve hypoplasia and dysplasia; dysplasia of the mitral (94%), tricuspid (56%), and pulmonary (11%) valves was also noted. Overall, 21 of 38 (55%) families had more than 1 affected individual, and 36% of participants had CVM, including 11% with BAV. The heritability of HLHS alone and with associated CVM were 99% and 74% (p < 0.00001), respectively. The sibling recurrence risk for HLHS was 8%, and for CVM was 22%.

CONCLUSIONS

The high heritability of HLHS suggests that it is determined largely by genetic factors. The frequent occurrence of left- and right-sided valve dysplasia in HLHS probands and the increased prevalence of BAV in family members suggests that HLHS is a severe form of valve malformation.

Evidence in favor of linkage to human chromosomal regions 18q, 5q and 13q for bicuspid aortic valve and associated cardiovascular malformations

The aim of this study was to identify regions of the genome that harbor genes influencing inheritance of bicuspid aortic valve (BAV) and/or associated cardiovascular malformation (CVM). Aortic valve disease is an important clinical problem, which often results in valve replacement, the second most common cardiac surgery in the United States. In every age group, a majority of cases of valve disease involves a BAV. BAV is the most common CVM with a reported prevalence of 1-2%. Heritability studies indicate that BAV determination is almost entirely genetic. We used a family-based genome-wide linkage analysis with microsatellite markers. Parametric and nonparametric analyses were performed with the software GENEHUNTER and SOLAR (Sequential Oligogenic Linkage Analysis Routines). Thirty-eight families (353 subjects) with BAV and/or associated CVM were assessed. Each participant underwent a standardized echocardiographic examination. The highest LOD score, 3.8, occurred on chromosome 18q between markers D18S68 and D18S1161. Two other chromosomal regions, 5q15-21 (between D5S644 and D5S2027) and 13q33-qter (between D13S1265 and 13qter), exhibited suggestive evidence of linkage (LOD > 2.0). Further, two previously reported linkage peaks on 9q34 and 17q24 were replicated in family specific analyses. No significant X chromosome linkage peaks were identified. In this genome-wide scan we demonstrate for the first time, that BAV and/or associated CVM exhibit linkage to chromosomes 18q, 5q and 13q. These regions likely contain genes whose mutation results in BAV and/or associated CVM indicating their important role in valvulogenesis and cardiac development.