Figure 1: Type of DNA damage, repair pathways and repair enzymes. SSBs are accomplished by base excision repair (BER) through PARP enzyme, nucleic acid excision repair (NER) through xeroderma pigmentosum (XP) enzyme and polymerases and mismatch repair (MMR) through MLH1 and MSH2. DSBs are corrected by the homologous recombination (HR) through several enzymes including ATM, ATR and BRCA1/2 and non-homologous end joining (NHEJ) through the DNA-dependent protein kinase (DNA-PKcs).