Provided is a method for treatment of pathologies caused by cells that have DNA sequences that differ from DNA of healthy human cells. The method utilises targeting of the sequence differences and effects cleavage of the DNA which does not occur in the healthy genome, whereby the cells containing the targeted DNA are killed or inactivated. Preferred systems for effecting such DNA damage is CRISPR systems where a CAS cleaves DNA adjacent to a sequence recognized by the CRISPR. Also disclosed are methods and a computer system for designing and/or producing the targeting nucleic acids.
