The gene-editing system CRISPR-Cas9 has revolutionized molecular biology, as it greatly simplifies altering gene sequences in a targeted fashion. It has already become an indispensable research tool, and early trials of its application for therapeutic purposes are now underway. In both laboratory and clinical settings, mutations introduced by the system must be restricted precisely to the targeted location (i.e. mutations elsewhere in the genome must be avoided) and the genetic alteration itself must be the intended one. However, the CRISPR systems currently in use are not entirely accurate, and can therefore introduce potentially harmful mutations both within the target gene and at other positions in the genome. LMU researchers led by neurobiologist and SyNergy member Dominik Paquet at the Institute for Stroke and Dementia Research now report the development of a simple method, which allows them to detect unintended alterations in the target gene itself. – Their results indicate that such on-target events occur at high frequency. Thus the new method represents an important contribution to ongoing efforts to improve the fidelity and efficacy of CRISPR-based gene editing in research, and as a potential means of correcting mutations associated with genetic diseases. The new findings appear in the journal Cell Reports.