Contribution of copy number variants to the risk of sporadic congenital heart disease

Abstract

Congenital heart disease (CHD) is the most common congenital malformation with a birth prevalence of 7/1000. CHD may occur as Mendelian syndromic disorders or as isolated conditions. The latter represent the majority (~80%) of CHD cases. Recent technological advancements have allowed large-scale genome-wide characterization of copy number variants (CNVs), which have been proposed to contribute to the risk of sporadic CHD. This thesis presents a genome-wide CNV study involving 2256 sporadic, isolated CHD patients, 283 trio CHD families, and 1538 ancestry-matched controls that were typed on the Illumina 660W-Q SNP platform. This was followed by an extensive validation study using comparative genomic hybridization arrays, multiplex ligation-dependent probe amplification and quantitative-fluorescent PCR assays. A global enrichment of rare genic deletions was identified in CHD patients (OR = 1.8, P = 0.001), compared to controls. Rare deletions that are associated with CHD had higher gene content (P = 0.001) and higher haploinsufficiency scores (P = 0.03). Additionally, they were enriched with genes involved in the Wnt signalling pathway, known for its pivotal role in cardiac morphogenesis. Rare de novo CNVs were also identified in ~5% CHD trios; 91% of which occurred on the paternal, as opposed to the maternal chromosome (P = 0.01). They spanned previously known candidate loci as well as novel loci for CHD. Individual locus enrichments in cases vs. controls were identified for CNVs at chromosomes 1q21.1 and 15q11.2. A phenotype-specific effect was observed for the 1q21.1 CNVs, and GJA5 was identified as the causative gene for CHD in this locus. In conclusion, global rare genic deletions contribute ~4% of the population attributable risk of sporadic CHD. CNVs implicating 1q21.1, 15q11.2 and Wnt signalling genes are associated with CHD. Rare de novo CNVs identified in CHD trios exhibit a paternal origin bias possibly of relevance to the epidemiology of CHD.