Visual inspection reveals a novel pathogenic mutation in PKD1 missed by the variant caller in whole-exome sequencing

Autosomal dominant polycystic kidney disease (ADPKD) is the most common type of inherited cystic kidney disease. The feasibility of whole-exome sequencing (WES) to obtain molecular diagnosis of ADPKD is still in question as previous studies showed conflicting results. Utilizing WES on a patient with ADPKD, standard bioinformatics pipeline demonstrated no pathogenic variant in the genes of interest. By visualizing read alignments using the Integrative Genomics Viewer, a region with atypical alignment of numerous soft-clipped reads at exon 45 of polycystin 1, transient receptor potential channel interacting (PKD1) gene was demonstrated. A total of four visual inspection steps were outlined to assess the origin of these soft-clipped reads as strand bias during capture, poor mapping, sequencing error or DNA template contamination. Following assessment, the atypical alignment at PKD1 was hypothesized to be caused by an insertion/deletion mutation. Sanger sequencing confirmed the presence of a novel 20-bp insertion in PKD1 (NM_001009944.3; c.12143_12144insTCCCCGCAGTCTTCCCCGCA; p.Val4048LeufsTer157), which introduced a premature stop codon and was predicted to be pathogenic. The present study demonstrated that WES could be utilized as a molecular diagnostic tool for ADPKD. Furthermore, visual inspection of read alignments was key in identifying the pathogenic variant. The proposed visual inspection steps may be incorporated into a typical WES data analysis workflow to improve the diagnostic yield.