Validation of a next generation sequencing panel for detection of hotspot cancer mutations in a clinical laboratory.

Recent advances in sequencing technologies have enabled us to scrutinize the versatile underlying mechanisms of cancer more precisely. However, adopting these new sophisticated technologies is challenging for clinical labs as it involves complex workflows, and requires validation for diagnostic purposes. The aim of this work is towards the analytical validation of a next generation sequencing (NGS) panel for cancer hotspot mutation analysis. Characterized formalin-fixed paraffin-embedded (FFPE) samples including biopsy specimens and cell-lines were examined by NGS methods utilizing the Ion Torrent™ Oncomine™ Focus DNA Assay and the PGM™ platform. Important parameters for somatic mutations including the threshold for differentiation of a positive and a negative result, coverage, sensitivity, specificity, and limit of detection (LoD) were analyzed. Variant calls with coverage of <100x were found to be inaccurate. The limit of detection for identifying hotspot mutations was determined to be 4.3%. The sensitivity and specificity of the method were 96.1% and 97.8% respectively. No statistically significant difference was found between different gene targets in terms of performance of hotspot frequency measurement for the subset tested. In every validation study, the number of samples, the manner of sample selection, and the number and type of variants play a role in the outcome. Therefore, these parameters should be assessed according to the clinical needs of each laboratory undertaking the validation.

HLA-A, -B, -DRB1 allele and haplotype frequencies of 920 cord blood units from Central Chile.

We present human leukocyte antigen (HLA) haplotype and allele/antigenic group frequencies derived from a data set of 920 umbilical cord blood units collected in Central Chile. HLA-A and -B genotypes were typed using sequence specific oligonucleotide probe methods while HLA-DRB1 genotypes were obtained from sequencing-based typing. The most frequent haplotype is A*29~B*44~DRB1*07:01 with an estimated frequency of 2.1%.

HLA-C locus allelic dropout in Sanger sequence-based typing due to intronic single nucleotide polymorphism.

We report a novel HLA-C allele that was identified during routine HLA typing using sequence-based methods. The patient was initially typed as a C*06:02, 06:04 with two nucleotide mismatches in exon 3, (C to T and T to G changes) which would have resulted in a non-synonymous mutation of a leucine residue being replaced with tryptophan. Further resolution of the patient's type by using sequence-specific primers (SSP) revealed that the companion allele to C*06:02 was a novel C*17:01. Confirmation of the existence of the new allele was performed across multiple platforms: Sanger sequencing, SSP, and Next Generation Sequencing (NGS) on the original sample and allele-specific clones for the entire HLA-C locus. The investigation revealed a single nucleotide mismatch within the Sanger sequencing primer binding site in intron 3. The mutation caused the initial C*17 dropout in exons 2 and 3. Further analysis of the Sanger and NGS data revealed that the C*17 had two additional unique positions in introns 2 and 7. The companion C*06:02 allele also possessed a novel position at intron 3. On August 31, 2013, the WHO nomenclature committee officially named the novel C*17:01 allele sequence as C*17:01:01:03 and the novel C*06:02 allele sequence as C*06:02:01:03.