Development and Validation of MPS-Based System for Human Appearance Prediction in Challenging Forensic Samples

Forensic DNA phenotyping (FDP) provides the ability to predict the human external traits from unknown sample donors, directly from minute amounts of DNA found at the crime scene. We developed a MPS multiplex assay, with the aim of genotyping all 41 DNA markers included in the HIrisPlex-S system for simultaneous prediction of eye, hair and skin colours. Forensic samples such as blood, skeletal remains, touch DNA, saliva swab, artificially degraded samples together with individuals with known phenotypes and a set of 2800 M control DNA were sequenced on the Ion Torrent platform in order to evaluate the concordance testing results and the forensic suitability of the 41-plex MPS assay. The panel was evaluated by testing a different number of PCR cycles and the volume of reagents for library preparation. The study demonstrated that full and reliable profiles were obtained with 0.1-5 ng, even with high degraded DNA. The increment of the number of PCR cycles results in an improvement of correctly genotyping and phenotyping for samples with low amounts of degraded DNA but higher frequencies of artefacts were found. The high DNA degradation level did not influence the correct genotyping and phenotyping and the critical parameter affecting the result is the quantity of input DNA. Eye and hair colour was predicted in 92.60% of individuals and skin color in 85.15% of individuals. The results suggest that this MPS assay is robust, highly sensitive, and useful for human pigmentation prediction in the forensic genetic field.