Browsing by Author "Gignoux, Christopher R."

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    Exome capture from saliva produces high quality genomic and metagenomic data
    (BioMed Central, 2014-04) Kidd, Jeffrey M.; Sharpton, Thomas J.; Bobo, Dean; Norman, Paul J.; Martin, Alicia R.; Carpenter, Meredith L.; Sikora, Martin; Gignoux, Christopher R.; Nemat-Gorgani, Neda; Adams, Alexandra; Guadalupe, Moraima; Guo, Xiaosen; Feng, Qiang; Li, Yingrui; Liu, Xiao; Parham, Peter; Hoal, Eileen G.; Feldman, Marcus W.; Pollard, Katherine S.; Wall, Jeffrey D.; Bustamante, Carlos D.; Henn, Brenna M.
    Background Targeted capture of genomic regions reduces sequencing cost while generating higher coverage by allowing biomedical researchers to focus on specific loci of interest, such as exons. Targeted capture also has the potential to facilitate the generation of genomic data from DNA collected via saliva or buccal cells. DNA samples derived from these cell types tend to have a lower human DNA yield, may be degraded from age and/or have contamination from bacteria or other ambient oral microbiota. However, thousands of samples have been previously collected from these cell types, and saliva collection has the advantage that it is a non-invasive and appropriate for a wide variety of research. Results We demonstrate successful enrichment and sequencing of 15 South African KhoeSan exomes and 2 full genomes with samples initially derived from saliva. The expanded exome dataset enables us to characterize genetic diversity free from ascertainment bias for multiple KhoeSan populations, including new exome data from six HGDP Namibian San, revealing substantial population structure across the Kalahari Desert region. Additionally, we discover and independently verify thirty-one previously unknown KIR alleles using methods we developed to accurately map and call the highly polymorphic HLA and KIR loci from exome capture data. Finally, we show that exome capture of saliva-derived DNA yields sufficient non-human sequences to characterize oral microbial communities, including detection of bacteria linked to oral disease (e.g. Prevotella melaninogenica). For comparison, two samples were sequenced using standard full genome library preparation without exome capture and we found no systematic bias of metagenomic information between exome-captured and non-captured data. Conclusions DNA from human saliva samples, collected and extracted using standard procedures, can be used to successfully sequence high quality human exomes, and metagenomic data can be derived from non-human reads. We find that individuals from the Kalahari carry a higher oral pathogenic microbial load than samples surveyed in the Human Microbiome Project. Additionally, rare variants present in the exomes suggest strong population structure across different KhoeSan populations.
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    Using multi-way admixture mapping to elucidate TB susceptibility in the South African Coloured population
    (BioMed Central, 2014-11) Daya, Michelle; Van der Merwe, Lize; Gignoux, Christopher R.; Van Helden, Paul D.; Moller, Marlo; Hoal, Eileen G.
    Background: The admixed South African Coloured population is ideally suited to the discovery of tuberculosis susceptibility genetic variants and their probable ethnic origins, but previous attempts at finding such variants using genome-wide admixture mapping were hampered by the inaccuracy of local ancestry inference. In this study, we infer local ancestry using the novel algorithm implemented in RFMix, with the emphasis on identifying regions of excess San or Bantu ancestry, which we hypothesize may harbour TB susceptibility genes. Results Using simulated data, we demonstrate reasonable accuracy of local ancestry inference by RFMix, with a tendency towards miss-calling San ancestry as Bantu. Regions with either excess San ancestry or excess African (San or Bantu) ancestry are less likely to be affected by this bias, and we therefore proceeded to identify such regions, found in cases but not in controls (642 cases and 91 controls). A number of promising regions were found (overall p-values of 7.19×10-5 for San ancestry and <2.00×10-16 for African ancestry), including chromosomes 15q15 and 17q22, which are close to genomic regions previously implicated in TB. Promising immune-related susceptibility genes such as the GADD45A, OSM and B7-H5 genes are also harboured in the identified regions. Conclusion Admixture mapping is feasible in the South African Coloured population and a number of novel TB susceptibility genomic regions were uncovered.