Objective Autosomal dominant progressive external ophthalmoplegia (adPEO) is a common adult onset disease secondary to nuclear DNA mutation.To date, there has been five genes associated with adPEO.The purpose of this study is to identify the gene responsible for causing adPEO in two Chinese families.Method Clinical, histochemical, and molecular genetics findings of 6 patients from two Chinese families with adPEO were collected.Histochemical study and long-range PCR assay were performed from the muscle biopsy specimens.Coding exons and flanking intron regions of twinkle gene were sequenced.