Comparison of different methods for repairing damaged DNA from buffered and unbuffered formalin-fixed tissues.

Formalin fixation is considered an important process for preservation of human tissue samples for long periods. However, this process not only results in cross-linking complicating isolation of nucleic acid but also introduces polymerase "blocks" during polymerase chain reaction (PCR). At present, many protocols have already been developed aiming at extracting high amounts of amplifiable DNA from formalin-fixed tissues (FFTs). However, there are few methods for repairing formalin-damaged DNA. In this study, we compared the effectiveness of several post-extraction enzymatic repair techniques, including Taq DNA polymerase, DNA polymerase I and T4 DNA ligase, the PreCR™ Repair Mix and Restorase® DNA Polymerase, in restoring STR profiles from formalin-damaged DNA. Our results indicated that formalin-damaged DNA may be repaired partly with Taq DNA polymerase and the Restorase® DNA Polymerase, and lost alleles may be restored and STR peak heights may increase upon repair with them. Moreover, the repair ability of the protocol 2 with Taq DNA polymerase surpasses the Restorase® DNA Polymerase.