LIG4 and cancer: The correlation between ineffective DNA repair and cancer risk is exemplified by the cancer proneness of patients with xeroderma pigmentosum (defective NER), DNA breakage syndromes (deficiencies in repair factors such as DNA ligase IV, NBS or ATM), Fanconi Anemia, Lynch Syndrome (DNA mismatch repair-deficient) and MUTYH-associated polyposis (impaired DNA 8-oxoGua processing).