Erroneous D7S820 genotypes caused by X.1 artefact removal in ForenSeq UAS v2.7.0 and their impact on forensic analyses

The latest release of ForenSeq Universal Analysis Software (UAS), version 2.7.0, introduces several major upgrades, including the implementation of bracketed formatting for short tandem repeats (STRs) and adoption of the International Society for Forensic Genetics minimum STR reporting range. Among these features, a new filter was implemented to remove the X.1 artefacts observed at the D7S820 locus, thereby reducing noise and simplifying data interpretation. In the present work, we evaluated the prevalence of X.1 artefacts, examined the behaviour of the new filtering implementation in UAS, and compared its performance with alternative analysis software. Our analysis revealed that samples containing genuine X.1 intermediate alleles presented incorrect allele assignments at the D7S820 locus, highlighting a potential impact on casework analyses.