toaSTR: A web-based forensic tool for the analysis of short tandem repeats in massively parallel sequencing data

We developed the web application toaSTR (www.toastr.de), a user-friendly tool for STR allele calling in MPS data independent of the instrument platform and the forensic kit used. toaSTR comes up with a clean, intuitive graphical user interface and well-documented parameter settings. Users can select from a wide range of STR markers to configure custom marker panels. This software supports both commercial and in-house multiplex PCR kits as well as various library preparation chemistries. Its sequence-based stutter-modelling algorithm automatically distinguishes biological (iso-)alleles, stutter, and artefacts to assist the interpretation of mixed samples. toaSTR features comprehensive data visualization with interactive diagrams and an adjustable tabular overview of sequence observations. Results are concordant with CE-based fragment analysis and can be exported for further analysis in biostatistical software or as PDF document with sequence description according to the ISFG-recommended nomenclature. An initial compatibility and concordance study confirmed the software's functionality and concordant allele calling across different MPS platforms, STR amplification kits, and library preparation chemistries.