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The use of whole-exome sequencing to disentangle complex phenotypes.

ABSTRACT: The success of whole-exome sequencing to identify mutations causing single-gene disorders has been well documented. In contrast whole-exome sequencing has so far had limited success in the identification of variants causing more complex phenotypes that seem unlikely to be due to the disruption of a single gene. We describe a family where two male offspring of healthy first cousin parents present a complex phenotype consisting of peripheral neuropathy and bronchiectasis that has not been described previously in the literature. Due to the fact that both children had the same problems in the context of parental consanguinity we hypothesised illness resulted from either X-linked or autosomal recessive inheritance. Through the use of whole-exome sequencing we were able to simplify this complex phenotype and identified a causative mutation (p.R1070*) in the gene periaxin (PRX), a gene previously shown to cause peripheral neuropathy (Dejerine-Sottas syndrome) when this mutation is present. For the bronchiectasis phenotype we were unable to identify a causal single mutation or compound heterozygote, reflecting the heterogeneous nature of this phenotype. In conclusion, in this study we show that whole-exome sequencing has the power to disentangle complex phenotypes through the identification of causative genetic mutations for distinct clinical disorders that were previously masked.

SUBMITTER: Williams HJ

PROVIDER: S-EPMC4717198 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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The use of whole-exome sequencing to disentangle complex phenotypes.

Williams Hywel J HJ Hurst John R JR Ocaka Louise L James Chela C Pao Caroline C Chanudet Estelle E Lescai Francesco F Stanescu Horia C HC Kleta Robert R Rosser Elisabeth E Bacchelli Chiara C Beales Philip P

European journal of human genetics : EJHG 20150610 2

The success of whole-exome sequencing to identify mutations causing single-gene disorders has been well documented. In contrast whole-exome sequencing has so far had limited success in the identification of variants causing more complex phenotypes that seem unlikely to be due to the disruption of a single gene. We describe a family where two male offspring of healthy first cousin parents present a complex phenotype consisting of peripheral neuropathy and bronchiectasis that has not been describe ...[more]

PMID: 26059842

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Project description:PurposeDemographic, environmental, and genetic risk factors for age-related macular degeneration (AMD) have been identified; however, a substantial portion of the variance in AMD disease risk and heritability remains unexplained. To identify AMD risk variants and generate hypotheses for future studies, we performed whole exome sequencing for 75 individuals whose phenotype was not well predicted by their genotype at known risk loci. We hypothesized that these phenotypically extreme individuals were more likely to carry rare risk or protective variants with large effect sizes.MethodsA genetic risk score was calculated in a case-control set of 864 individuals (467 AMD cases, 397 controls) based on 19 common (≥1% minor allele frequency, MAF) single nucleotide variants previously associated with the risk of advanced AMD in a large meta-analysis of advanced cases and controls. We then selected for sequencing 39 cases with bilateral choroidal neovascularization with the lowest genetic risk scores to detect risk variants and 36 unaffected controls with the highest genetic risk score to detect protective variants. After minimizing the influence of 19 common genetic risk loci on case-control status, we targeted single variants of large effect and the aggregate effect of weaker variants within genes and pathways. Single variant tests were conducted on all variants, while gene-based and pathway analyses were conducted on three subsets of data: 1) rare (≤1% MAF in the European population) stop, splice, or damaging missense variants, 2) all rare variants, and 3) all variants. All analyses controlled for the effects of age and sex.ResultsNo variant, gene, or pathway outside regions known to be associated with risk for advanced AMD reached genome-wide significance. However, we identified several variants with substantial differences in allele frequency between cases and controls with strong additive effects on affection status after controlling for age and sex. Protective effects trending toward significance were detected at two loci identified in single-variant analyses: an intronic variant in FBLN7 (the gene encoding fibulin 7) and at three variants near pyridoxal (pyridoxine, vitamin B6) kinase (PDXK). Aggregate rare-variant analyses suggested evidence for association at ASRGL1, a gene previously linked to photoreceptor cell death, and at BSDC1. In known AMD loci we also identified 29 novel or rare damaging missense or stop/splice variants in our sample of cases and controls.ConclusionsIdentified variants and genes may highlight regions important in the pathogenesis of AMD and are key targets for replication.

Project description:ImportanceMitochondrial disorders have emerged as a common cause of inherited disease, but their diagnosis remains challenging. Multiple respiratory chain complex defects are particularly difficult to diagnose at the molecular level because of the massive number of nuclear genes potentially involved in intramitochondrial protein synthesis, with many not yet linked to human disease.ObjectiveTo determine the molecular basis of multiple respiratory chain complex deficiencies.Design, setting, and participantsWe studied 53 patients referred to 2 national centers in the United Kingdom and Germany between 2005 and 2012. All had biochemical evidence of multiple respiratory chain complex defects but no primary pathogenic mitochondrial DNA mutation. Whole-exome sequencing was performed using 62-Mb exome enrichment, followed by variant prioritization using bioinformatic prediction tools, variant validation by Sanger sequencing, and segregation of the variant with the disease phenotype in the family.ResultsPresumptive causal variants were identified in 28 patients (53%; 95% CI, 39%-67%) and possible causal variants were identified in 4 (8%; 95% CI, 2%-18%). Together these accounted for 32 patients (60% 95% CI, 46%-74%) and involved 18 different genes. These included recurrent mutations in RMND1, AARS2, and MTO1, each on a haplotype background consistent with a shared founder allele, and potential novel mutations in 4 possible mitochondrial disease genes (VARS2, GARS, FLAD1, and PTCD1). Distinguishing clinical features included deafness and renal involvement associated with RMND1 and cardiomyopathy with AARS2 and MTO1. However, atypical clinical features were present in some patients, including normal liver function and Leigh syndrome (subacute necrotizing encephalomyelopathy) seen in association with TRMU mutations and no cardiomyopathy with founder SCO2 mutations. It was not possible to confidently identify the underlying genetic basis in 21 patients (40%; 95% CI, 26%-54%).Conclusions and relevanceExome sequencing enhances the ability to identify potential nuclear gene mutations in patients with biochemically defined defects affecting multiple mitochondrial respiratory chain complexes. Additional study is required in independent patient populations to determine the utility of this approach in comparison with traditional diagnostic methods.

Project description:BackgroundGenomically-guided clinical trials are performed across different tumor types sharing genetic mutations, but trial organization remains complex. Here we address the feasibility and utility of routine somatic and constitutional exome analysis in metastatic cancer patients.MethodsExoma trial (NCT02840604) is a multicenter, prospective clinical trial. Eligible patients presented a metastatic cancer progressing after at least one line of systemic therapy. Constitutional genetics testing required geneticist consultation. Somatic and germline exome analysis was restricted to 317 genes. Variants were classified and molecular tumor board made therapeutic recommendations based on ESMO guidelines. Primary endpoint was the feasibility of the approach evaluated by the proportion of patient that received a therapeutic proposal.FindingsBetween May 2016 and October 2018, 506 patients were included. Median time required for tumor sample reception was 8 days. Median time from sample reception to results was 52 days. Somatic analysis was performed for 456 patients (90.1%). Both somatic and constitutional analyses were successfully performed for 386 patients (76.3%). In total, 342 patients (75%) received a therapeutic proposal. Genetic susceptibility to cancer was found in 35 (9%) patients. Only, 79 patients (23.1%) were treated with NGS matched therapy mainly PI3K/AKT/mTOR inhibitors 22 (27.8%), followed by PARP inhibitors 19 (24.1%), antiangiogenics 17 (21.5%), MEK inhibitors 7 (8.9%) and immunotherapy 5 (6.3%). Matched treatment was finally stopped because of disease progression 50 (63%), treatment toxicity 18 (23%), patients' death 4 (5%). PFS2/PFS1 ratio was > 1,3 for 23,5% of patients treated with the NGS matched therapy and 23,7% of patients treated with standard therapy.InterpretationStudy shows that exome analysis is feasible in cancer routine care. This strategy improves detection of genetic predispositions and enhances access to target therapies. However, no differences were observed between PFS ratios of patients treated with matched therapy versus standard therapy.FundingThis work was funding by the centre Georges Francois Leclerc.

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The use of whole-exome sequencing to disentangle complex phenotypes.

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The use of whole-exome sequencing to disentangle complex phenotypes.

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