Evaluating the performance of a clinical genome sequencing program for diagnosis of rare genetic disease, seen through the lens of craniosynostosis.

PURPOSE: Genome sequencing (GS) for diagnosis of rare genetic disease is being introduced into the clinic, but the complexity of the data poses challenges for developing pipelines with high diagnostic sensitivity. We evaluated the performance of the Genomics England 100,000 Genomes Project (100kGP) panel-based pipelines, using craniosynostosis as a test disease. METHODS: GS data from 114 probands with craniosynostosis and their relatives (314 samples), negative on routine genetic testing, were scrutinized by a specialized research team, and diagnoses compared with those made by 100kGP. RESULTS: Sixteen likely pathogenic/pathogenic variants were identified by 100kGP. Eighteen additional likely pathogenic/pathogenic variants were identified by the research team, indicating that for craniosynostosis, 100kGP panels had a diagnostic sensitivity of only 47%. Measures that could have augmented diagnoses were improved calling of existing panel genes (+18% sensitivity), review of updated panels (+12%), comprehensive analysis of de novo small variants (+29%), and copy-number/structural variants (+9%). Recent NHS England recommendations that partially incorporate these measures should achieve 85% overall sensitivity (+38%). CONCLUSION: GS identified likely pathogenic/pathogenic variants in 29.8% of previously undiagnosed patients with craniosynostosis. This demonstrates the value of research analysis and the importance of continually improving algorithms to maximize the potential of clinical GS.

Scaling national and international improvement in virtual gene panel curation via a collaborative approach to discordance resolution.

Clinical validity assessments of gene-disease associations underpin analysis and reporting in diagnostic genomics, and yet wide variability exists in practice, particularly in use of these assessments for virtual gene panel design and maintenance. Harmonization efforts are hampered by the lack of agreed terminology, agreed gene curation standards, and platforms that can be used to identify and resolve discrepancies at scale. We undertook a systematic comparison of the content of 80 virtual gene panels used in two healthcare systems by multiple diagnostic providers in the United Kingdom and Australia. The process was enabled by a shared curation platform, PanelApp, and resulted in the identification and review of 2,144 discordant gene ratings, demonstrating the utility of sharing structured gene-disease validity assessments and collaborative discordance resolution in establishing national and international consensus.

Targeted genetic testing for familial hypercholesterolaemia using next generation sequencing: a population-based study.

BACKGROUND: Familial hypercholesterolaemia (FH) is a common Mendelian condition which, untreated, results in premature coronary heart disease. An estimated 88% of FH cases are undiagnosed in the UK. We previously validated a method for FH mutation detection in a lipid clinic population using next generation sequencing (NGS), but this did not address the challenge of identifying index cases in primary care where most undiagnosed patients receive healthcare. Here, we evaluate the targeted use of NGS as a potential route to diagnosis of FH in a primary care population subset selected for hypercholesterolaemia. METHODS: We used microfluidics-based PCR amplification coupled with NGS and multiplex ligation-dependent probe amplification (MLPA) to detect mutations in LDLR, APOB and PCSK9 in three phenotypic groups within the Generation Scotland: Scottish Family Health Study including 193 individuals with high total cholesterol, 232 with moderately high total cholesterol despite cholesterol-lowering therapy, and 192 normocholesterolaemic controls. RESULTS: Pathogenic mutations were found in 2.1% of hypercholesterolaemic individuals, in 2.2% of subjects on cholesterol-lowering therapy and in 42% of their available first-degree relatives. In addition, variants of uncertain clinical significance (VUCS) were detected in 1.4% of the hypercholesterolaemic and cholesterol-lowering therapy groups. No pathogenic variants or VUCS were detected in controls. CONCLUSIONS: We demonstrated that population-based genetic testing using these protocols is able to deliver definitive molecular diagnoses of FH in individuals with high cholesterol or on cholesterol-lowering therapy. The lower cost and labour associated with NGS-based testing may increase the attractiveness of a population-based approach to FH detection compared to genetic testing with conventional sequencing. This could provide one route to increasing the present low percentage of FH cases with a genetic diagnosis.

The use of next-generation sequencing in clinical diagnosis of familial hypercholesterolemia.

PURPOSE: Familial hypercholesterolemia is a common Mendelian disorder associated with early-onset coronary heart disease that can be treated by cholesterol-lowering drugs. The majority of cases in the United Kingdom are currently without a molecular diagnosis, which is partly due to the cost and time associated with standard screening techniques. The main purpose of this study was to test the sensitivity and specificity of two next-generation sequencing protocols for genetic diagnosis of familial hypercholesterolemia. METHODS: Libraries were prepared for next-generation sequencing by two target enrichment protocols; one using the SureSelect Target Enrichment System and the other using the PCR-based Access Array platform. RESULTS: In the validation cohort, both protocols showed 100% specificity, whereas the sensitivity for short variant detection was 100% for the SureSelect Target Enrichment and 98% for the Access Array protocol. Large deletions/duplications were only detected using the SureSelect Target Enrichment protocol. In the prospective cohort, the mutation detection rate using the Access Array was highest in patients with clinically definite familial hypercholesterolemia (67%), followed by patients with possible familial hypercholesterolemia (26%). CONCLUSION: We have shown the potential of target enrichment methods combined with next-generation sequencing for molecular diagnosis of familial hypercholesterolemia. Adopting these assays for patients with suspected familial hypercholesterolemia could improve cost-effectiveness and increase the overall number of patients with a molecular diagnosis.

Identification and biochemical analysis of a novel APOB mutation that causes autosomal dominant hypercholesterolemia.

Patients with autosomal dominant hypercholesterolemia (ADH) have a high risk of developing cardiovascular disease that can be effectively treated using statin drugs. Molecular diagnosis and family cascade screening is recommended for early identification of individuals at risk, but up to 40% of families have no mutation detected in known genes. This study combined linkage analysis and exome sequencing to identify a novel variant in exon 3 of APOB (Arg50Trp). Mass spectrometry established that low-density lipoprotein (LDL) containing Arg50Trp APOB accumulates in the circulation of affected individuals, suggesting defective hepatic uptake. Previously reported mutations in APOB causing ADH have been located in exon 26. This is the first report of a mutation outside this region causing this phenotype, therefore, more extensive screening of this large and highly polymorphic gene may be necessary in ADH families. This is now feasible due to the high capacity of recently available sequencing platforms.

Mild case of Curry-Jones syndrome.

The main features of the Curry-Jones syndrome are syndactyly, pre-axial polydactyly, craniosynostosis, absent corpus callosum, skin anomalies (characteristic pearly white areas that become scarred and atrophic, with increased hair growth), colobomas or microphthalmia and intestinal obstruction because of multiple benign myofibromata of the large bowel. Developmental delay occurs in half of the reported patients. The patient reported here has a mild form of the condition with polysyndactyly and skin changes but no craniosynostosis, bowel problems or developmental delay.