Nonalcoholic fatty liver disease is a major liver disease that leads to cirrhosis and/or hepatocellular carcinoma in a subset of patients. The mechanism underlying disease progression is largely unknown. p53-binding protein 1 (53BP1) is a DNA damage response protein that rapidly localizes at the site of DNA double-strand breaks. In this study, we investigated nuclear 53BP1-positive foci formation as an indicator of DNA double-strand breaks in human nonalcoholic fatty liver disease liver tissues by immunofluorescence microscopy. A total of 52 liver tissue samples, including 43 nonalcoholic fatty liver disease samples and 9 controls, were studied. Our results show that the number of abnormal 53BP1-positive foci in hepatocytes (defined as three or more discrete nuclear foci and/or large foci greater than 1 μM) was significantly increased in nonalcoholic fatty liver disease patients compared to that in controls, both in nonalcoholic fatty liver (p
