GENETIC STUDIES OF COMMON CONGENITAL HEART DEFECTS

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The goal of this proposal is to carry out genetic studies of three classes of congenital heart defects (CHD): left ventricular outflow tract obstruction (LVOTO); Laterality defects, and cardiac neural crest migration defect. Left-sided obstructive lesions account for approximately 14 percent of all congenital heart defects and are important contributors to overall neonatal mortality. Neural crest migration defects account for an additional 10 percent and defects of left-right asymmetry approximately 3 percent. Although various lines of embryological, epidemiological, and cytogenetic evidence point to the importance of genetic factors, the fact that most cases are sporadic indicates that the genetic components are complex and do not conform to a simple pattern of inheritance. The first Specific Aim of this proposal will initiate and extend a linkage approach to LVOTO and Laterality genetics. We have confirmed a significant occurrence of subclinical structural heart defects in the parents of affected children, supporting a model in which hemodynamically severe defects reflected a threshold trait. These data are also consistent with a supgroup of cases due to dominant inheritance with reduced penetrance and, indeed, we have ascertained at least 19 LVOTO and 35 Laterality families. Echocardiography studies in LVOTO parents suggest that quantitative measurement might be useful in delineating the liability distribution underlying the threshold. We propose to carry out a larger and more comprehensive evaluation of echocardiography in parents and sibs of LVOTO patients. If successful, these data will be used to map one or more loci contributing to left heart development (as quantitative trait loci - QTL) using sib pair and extended pedigree study designs. The second Specific Aim is to establish and test case/parent trios in Linkage/Association analyses in both LVOTO and Laterality defects. We have collected cell and DNA samples from almost 500 isolated cases that can be used in case-control studies and for mutation analyses. Affected-child/parent trios will be used in linkage/association studies using transmission disequilibrium (TDT) and likelihood ratio (LRT) analyses, as well as in mutational screening. Approximately 50 candidate genes, suggested primarily by the phenotypes of mouse knockouts, will be examined. The third Specific Aim will exploit a unique sample set from children with CHARGE Association. This complex phenotype has a substantial possibility of arising from a contiguous gene deletion. Case-parent trios offer an outstanding opportunity to test extremely dense SNP marker maps in a screen for absence of expected heterozygosity in the affecteds. Identification of genes involved in CHARGE should provide both mechanistic insights and candidate genes for isolated heart defects. The proposed studies will provide a base on which to advance genetic analyses of a substantial group of congenital heart defects with the aim of reducing their occurrence and providing new treatment opportunities.