Genetics of congenital heart diseases

Development of the cardiac atrial septum involves complex morphogenetic processes including programmed cell growth and death. Secundum atrial septal defect (ASDII) and patent foramen ovale (PFO) are common atrial septal anomalies associated with numerous pathologies including stroke. Data from studies in humans and mouse suggest that PFO and ASDII exist in an anatomical continuum of septal dysmorphogenesis with a common genetic basis.Analysis of quantitative trait loci (QTL) and genome technology form a powerful approach to understand genetic complexity underpinning common disease. A previous study of inbred mice mapped QTL for quantitative anatomical atrial septal parameters correlating with PFO, including flap valve length (FVL) and foramen ovale width (FOW). Here, we explore an advanced intercross line (AIL) for confirmation and fine mapping of these QTL. An AIL between parental strains QSi5 and 129T2/SvEms, showing extreme values for FVL and PFO, was established over 14 generations. Linkage analysis using 141 single nucleotide polymorphism markers focused on 6 significant and one suggestive QTL regions for FVL or FOW found previously, and we also sought QTL for heart weight (HW) normalized to body weight (BW). Virtually all QTL were confirmed and refined and many new QTL were discovered, with analysis of PFO as a binary trait providing strong support. QTL were not explained by HW/BW differences between parental strains. The overlap between FVL and FOW QTL was striking, indicating many QTL affect processes relevant to both septum primum and septum secundum. This study provides a high-resolution picture of genetic complexity underpinning atrial septal variation in the mouse and predicts involvement of potentially hundreds of risk variants in humans.Subsequently, high throughput sequencing of the whole genomes of the parental lines and analysis of HapMap datasets as a validation method, in addition to applying a multi-step filtering criteria resulted in identification of gene variants underlying QTL, and candidates for involvement in phenotypic variation based on the predicted impact of sequence changes.Mutations in multiple members of the evolutionarily conserved cardiac transcription factor network, including GATA4, cause or predispose to ASDII and PFO. Here, we assessed whether the most prevalent variant of the GATA4 gene, S377G, was significantly associated with PFO or ASD. Our analysis of world indigenous populations showed that GATA4 S377G was largely Caucasian-specific, and so subjects were restricted to those of Caucasian descent. To select for patients with larger PFO, we limited our analysis to those with cryptogenic stroke in which PFO was a subsequent finding. In an initial study of Australian subjects, a weak association between GATA4 S377G and PFO/Stroke was observed. However, in a follow up study of German Caucasians no association was found with either PFO or ASD. Analysis of combined Australian and German data confirmed the lack of association. Thus, the common GATA4 variant S377G is likely to be relatively benign in terms of its participation in CHD and PFO/Stroke