Human Genetics

, Volume 135, Issue 5, pp 499–511 | Cite as

Amplicon-based semiconductor sequencing of human exomes: performance evaluation and optimization strategies

  • E. Damiati
  • G. Borsani
  • Edoardo GiacopuzziEmail author
Original Investigation


The Ion Proton platform allows to perform whole exome sequencing (WES) at low cost, providing rapid turnaround time and great flexibility. Products for WES on Ion Proton system include the AmpliSeq Exome kit and the recently introduced HiQ sequencing chemistry. Here, we used gold standard variants from GIAB consortium to assess the performances in variants identification, characterize the erroneous calls and develop a filtering strategy to reduce false positives. The AmpliSeq Exome kit captures a large fraction of bases (>94 %) in human CDS, ClinVar genes and ACMG genes, but with 2,041 (7 %), 449 (13 %) and 11 (19 %) genes not fully represented, respectively. Overall, 515 protein coding genes contain hard-to-sequence regions, including 90 genes from ClinVar. Performance in variants detection was maximum at mean coverage >120×, while at 90× and 70× we measured a loss of variants of 3.2 and 4.5 %, respectively. WES using HiQ chemistry showed ~71/97.5 % sensitivity, ~37/2 % FDR and ~0.66/0.98 F1 score for indels and SNPs, respectively. The proposed low, medium or high-stringency filters reduced the amount of false positives by 10.2, 21.2 and 40.4 % for indels and 21.2, 41.9 and 68.2 % for SNP, respectively. Amplicon-based WES on Ion Proton platform using HiQ chemistry emerged as a competitive approach, with improved accuracy in variants identification. False-positive variants remain an issue for the Ion Torrent technology, but our filtering strategy can be applied to reduce erroneous variants.


Variant Identification Exome Sequencing Whole Exome Sequencing Torrent Variant Caller High Confident Region 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We acknowledge Prof. Massimo Gennarelli, Prof. Emilio Sacchetti, Prof. Marina Colombi and Dr. Chiara Magri for providing materials used in the study and let us include their samples data. Publication costs were covered by Grant “New Opportunities and Ways towards ERC” (NOW ERC, Project: 2014-2256) from Fondazione Cariplo and Regione Lombardia.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

For this type of study formal consent is not required.

Supplementary material

439_2016_1656_MOESM1_ESM.xls (10 kb)
Detailed results of the comparison of exome capture kits assessed in the study (XLS 9 kb)
439_2016_1656_MOESM2_ESM.xls (33.4 mb)
Supplementary tables 1–6. Lists of CDS regions not fully addressed in the 6 exome enrichment kits compared in the study. Gene symbol and ClinVar annotation are also reported (XLS 34183 kb)
439_2016_1656_MOESM3_ESM.pdf (40 kb)
Supplementary tables 7–8. Detailed results of the 27 sequencing runs and 34 exome sequencing data analyzed in the study (PDF 40 kb)
439_2016_1656_MOESM4_ESM.xls (128 kb)
Supplementary table 9. List of regions within human CDS exons that emerged as hard to sequence intervals based on our analysis. Gene symbols and ClinVar annotations are also reported (XLS 127 kb)
439_2016_1656_MOESM5_ESM.xls (11 kb)
Supplementary table 10. Detailed results on variant identification performances on the NA12878 sample, determined by comparison of WES datasets with gold standard variants provided by the GIAB consortium (XLS 11 kb)
439_2016_1656_MOESM6_ESM.pdf (1.6 mb)
Supplementary figures cited in the paper with figure legends (PDF 1661 kb)


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© The Author(s) 2016

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  1. 1.Unit of Genetics, Department of Molecular and Translational MedicineUniversity of BresciaBresciaItaly

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