Junho Kim1, Ju Heon Maeng1, Jae Seok Lim2, Hyeonju Son1, Junehawk Lee3, Jeong Ho Lee2 and Sangwoo Kim1,*
1 Severance Biomedical Science Institute, Brain Korea 21 PLUS Project for Medical Sciences, Yonsei University College of Medicine, Seoul 03722, South Korea, 2Graduate School of Medical Science and Engineering, KAIST, Daejeon 34141, South Korea and 3Department of Convergence Technology Research, Korea Institute of Science and Technology Information, Daejeon 34141, South Korea
*To whom correspondence should be addressed
Motivation: Advances in sequencing technologies have remarkably lowered the detection limit of somatic variants to a low frequency. However, calling mutations at this range is still confounded by many factors including environmental contamination. Vector contamination is a continuously occurring issue and is especially problematic since vector inserts are hardly distinguishable from the sample sequences. Such inserts, which may harbor polymorphisms and engineered functional mutations, can result in calling false variants at corresponding sites. Numerous vector-screening methods have been developed, but none could handle contamination from inserts because they are focusing on vector backbone sequences alone.
Results: We developed a novel method-Vecuum-that identifies vector-originated reads and resultant false variants. Since vector inserts are generally constructed from intron-less cDNAs, Vecuum identifies vector-originated reads by inspecting the clipping patterns at exon junctions. False variant calls are further detected based on the biased distribution of mutant alleles to vector-originated reads. Tests on simulated and spike-in experimental data validated that Vecuum could detect 93% of vector contaminants and could remove up to 87% of variant-like false calls with 100% precision. Application to public sequence datasets demonstrated the utility of Vecuum in detecting false variants resulting from various types of external contamination.
Availability and Implementation: Java-based implementation of the method is available at http://vecuum.sourceforge.net/
Supplementary information:Supplementary data are available at Bioinformatics online.