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

PhD ThesisCongenital 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

Phenotype-specific effect of chromosome 1q21.1 rearrangements and GJA5 duplications in 2436 congenital heart disease patients and 6760 controls

Recurrent rearrangements of chromosome 1q21.1 that occur via non-allelic homologous recombination have been associated with variable phenotypes exhibiting incomplete penetrance, including congenital heart disease (CHD). However, the gene or genes within the ∼1 Mb critical region responsible for each of the associated phenotypes remains unknown. We examined the 1q21.1 locus in 948 patients with tetralogy of Fallot (TOF), 1488 patients with other forms of CHD and 6760 ethnically matched controls using single nucleotide polymorphism genotyping arrays (Illumina 660W and Affymetrix 6.0) and multiplex ligation-dependent probe amplification. We found that duplication of 1q21.1 was more common in cases of TOF than in controls [odds ratio (OR) 30.9, 95% confidence interval (CI) 8.9-107.6); P = 2.2 × 10−7], but deletion was not. In contrast, deletion of 1q21.1 was more common in cases of non-TOF CHD than in controls [OR 5.5 (95% CI 1.4-22.0); P = 0.04] while duplication was not. We also detected rare (n = 3) 100-200 kb duplications within the critical region of 1q21.1 in cases of TOF. These small duplications encompassed a single gene in common, GJA5, and were enriched in cases of TOF in comparison to controls [OR = 10.7 (95% CI 1.8-64.3), P = 0.01]. These findings show that duplication and deletion at chromosome 1q21.1 exhibit a degree of phenotypic specificity in CHD, and implicate GJA5 as the gene responsible for the CHD phenotypes observed with copy number imbalances at this locu

Phenotype-specific effect of chromosome 1q21.1 rearrangements and GJA5 duplications in 2436 congenital heart disease patients and 6760 controls

Recurrent rearrangements of chromosome 1q21.1 that occur via non-allelic homologous recombination have been associated with variable phenotypes exhibiting incomplete penetrance, including congenital heart disease (CHD). However, the gene or genes within the ∼1 Mb critical region responsible for each of the associated phenotypes remains unknown. We examined the 1q21.1 locus in 948 patients with tetralogy of Fallot (TOF), 1488 patients with other forms of CHD and 6760 ethnically matched controls using single nucleotide polymorphism genotyping arrays (Illumina 660W and Affymetrix 6.0) and multiplex ligation-dependent probe amplification. We found that duplication of 1q21.1 was more common in cases of TOF than in controls [odds ratio (OR) 30.9, 95% confidence interval (CI) 8.9–107.6); P = 2.2 × 10−7], but deletion was not. In contrast, deletion of 1q21.1 was more common in cases of non-TOF CHD than in controls [OR 5.5 (95% CI 1.4–22.0); P = 0.04] while duplication was not. We also detected rare (n = 3) 100–200 kb duplications within the critical region of 1q21.1 in cases of TOF. These small duplications encompassed a single gene in common, GJA5, and were enriched in cases of TOF in comparison to controls [OR = 10.7 (95% CI 1.8–64.3), P = 0.01]. These findings show that duplication and deletion at chromosome 1q21.1 exhibit a degree of phenotypic specificity in CHD, and implicate GJA5 as the gene responsible for the CHD phenotypes observed with copy number imbalances at this locus

Genome-wide association study identifies loci on 12q24 and 13q32 associated with Tetralogy of Fallot

We conducted a genome-wide association study to search for risk alleles associated with Tetralogy of Fallot (TOF), using a northern European discovery set of 835 cases and 5159 controls. A region on chromosome 12q24 was associated (P = 1.4 × 10−7) and replicated convincingly (P = 3.9 × 10−5) in 798 cases and 2931 controls [per allele odds ratio (OR) = 1.27 in replication cohort, P = 7.7 × 10−11 in combined populations]. Single nucleotide polymorphisms in the glypican 5 gene on chromosome 13q32 were also associated (P = 1.7 × 10−7) and replicated convincingly (P = 1.2 × 10−5) in 789 cases and 2927 controls (per allele OR = 1.31 in replication cohort, P = 3.03 × 10−11 in combined populations). Four additional regions on chromosomes 10, 15 and 16 showed suggestive association accompanied by nominal replication. This study, the first genome-wide association study of a congenital heart malformation phenotype, provides evidence that common genetic variation influences the risk of TO

An international effort towards developing standards for best practices in analysis, interpretation and reporting of clinical genome sequencing results in the CLARITY Challenge

There is tremendous potential for genome sequencing to improve clinical diagnosis and care once it becomes routinely accessible, but this will require formalizing research methods into clinical best practices in the areas of sequence data generation, analysis, interpretation and reporting. The CLARITY Challenge was designed to spur convergence in methods for diagnosing genetic disease starting from clinical case history and genome sequencing data. DNA samples were obtained from three families with heritable genetic disorders and genomic sequence data were donated by sequencing platform vendors. The challenge was to analyze and interpret these data with the goals of identifying disease-causing variants and reporting the findings in a clinically useful format. Participating contestant groups were solicited broadly, and an independent panel of judges evaluated their performance. RESULTS: A total of 30 international groups were engaged. The entries reveal a general convergence of practices on most elements of the analysis and interpretation process. However, even given this commonality of approach, only two groups identified the consensus candidate variants in all disease cases, demonstrating a need for consistent fine-tuning of the generally accepted methods. There was greater diversity of the final clinical report content and in the patient consenting process, demonstrating that these areas require additional exploration and standardization. CONCLUSIONS: The CLARITY Challenge provides a comprehensive assessment of current practices for using genome sequencing to diagnose and report genetic diseases. There is remarkable convergence in bioinformatic techniques, but medical interpretation and reporting are areas that require further development by many groups

Chromosomal Imbalances in Patients with Congenital Cardiac Defects: A Meta‐analysis Reveals Novel Potential Critical Regions Involved in Heart Development

ObjectiveCongenital cardiac defects represent the most common group of birth defects, affecting an estimated six per 1000 births. Genetic characterization of patients and families with cardiac defects has identified a number of genes required for heart development. Yet, despite the rapid pace of these advances, mutations affecting known genes still account for only a small fraction of congenital heart defects suggesting that many more genes and developmental mechanisms remain to be identified.DesignIn this study, we reviewed 1694 described cases of patients with cardiac defects who were determined to have a significant chromosomal imbalance (a deletion or duplication). The cases were collected from publicly available databases (DECIPHER, ISCA, and CHDWiki) and from recent publications. An additional 68 nonredundant cases were included from the University of Michigan. Cases with multiple chromosomal or whole chromosome defects (trisomy 13, 18, 21) were excluded, and cases with overlapping deletions and/or insertions were grouped to identify regions potentially involved in heart development.ResultsSeventy‐nine chromosomal regions were identified in which 5 or more patients had overlapping imbalances. Regions of overlap were used to determine minimal critical domains most likely to contain genes or regulatory elements involved in heart development. This approach was used to refine the critical regions responsible for cardiac defects associated with chromosomal imbalances involving 1q24.2, 2q31.1, 15q26.3, and 22q11.2.ConclusionsThe pattern of chromosomal imbalances in patients with congenital cardiac defects suggests that many loci may be involved in normal heart development, some with very strong and direct effects and others with less direct effects. Chromosomal duplication/deletion mapping will provide an important roadmap for genome‐wide sequencing and genetic mapping strategies to identify novel genes critical for heart development.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111936/1/chd12179.pd

Hereditary cancer genes are highly susceptible to splicing mutations

<div><p>Substitutions that disrupt pre-mRNA splicing are a common cause of genetic disease. On average, 13.4% of all hereditary disease alleles are classified as splicing mutations mapping to the canonical 5′ and 3′ splice sites. However, splicing mutations present in exons and deeper intronic positions are vastly underreported. A recent re-analysis of coding mutations in exon 10 of the Lynch Syndrome gene, <i>MLH1</i>, revealed an extremely high rate (77%) of mutations that lead to defective splicing. This finding is confirmed by extending the sampling to five other exons in the <i>MLH1</i> gene. Further analysis suggests a more general phenomenon of defective splicing driving Lynch Syndrome. Of the 36 mutations tested, 11 disrupted splicing. Furthermore, analyzing past reports suggest that <i>MLH1</i> mutations in canonical splice sites also occupy a much higher fraction (36%) of total mutations than expected. When performing a comprehensive analysis of splicing mutations in human disease genes, we found that three main causal genes of Lynch Syndrome, <i>MLH1</i>, <i>MSH2</i>, and <i>PMS2</i>, belonged to a class of 86 disease genes which are enriched for splicing mutations. Other cancer genes were also enriched in the 86 susceptible genes. The enrichment of splicing mutations in hereditary cancers strongly argues for additional priority in interpreting clinical sequencing data in relation to cancer and splicing.</p></div

Non-uniform distribution of splicing mutations across disease genes.

<p><b>A.</b> SSM versus all exonic mutations in the HGMD with regions of 99.9% confidence interval shown in gray. Genes with more, expected, and less SSM are shown in red (Upper), blue (Expected), and green (Lower), respectively. Location of <i>MLH1</i>, <i>MSH2</i>, and <i>PMS2</i> are highlighted and labeled. <b>B.</b> Percent ESM of total mutations tested using MaPSy in each category. <b>C</b>. Due to the inability of MaPSy to observe mutant-specific exon skipping events (as a result of the identical flanking exons), ESMs found in MLH1, BRCA1, and OPA1 were validated as individual wildtype and mutant minigene constructs. All three mutant constructs showed exon skipping events, which were not shown in wildtype constructs.</p

Genome-wide association study of multiple congenital heart disease phenotypes identifies a susceptibility locus for atrial septal defect at chromosome 4p16

We carried out a genome-wide association study (GWAS) of congenital heart disease (CHD). Our discovery cohort comprised 1,995 CHD cases and 5,159 controls and included affected individuals from each of the 3 major clinical CHD categories (with septal, obstructive and cyanotic defects). When all CHD phenotypes were considered together, no region achieved genome-wide significant association. However, a region on chromosome 4p16, adjacent to the MSX1 and STX18 genes, was associated (P = 9.5 × 10-7) with the risk of ostium secundum atrial septal defect (ASD) in the discovery cohort (N = 340 cases), and this association was replicated in a further 417 ASD cases and 2,520 controls (replication P = 5.0 × 10-5; odds ratio (OR) in replication cohort = 1.40, 95% confidence interval (CI) = 1.19-1.65; combined P = 2.6 × 10-10). Genotype accounted for ∼9% of the population-attributable risk of ASD