AdPEO and other hereditary disorders with multiple mtDNA deletions have been found associated with mutations in some nuclear genes, such as thymidine phosphorylase gene (TYMP, previously known as ECGF1), solute carrier family 25 (mitochondrial carrier; adenine nucleotide translocator) member 4 gene (SLC25A4, previously known as ANT1), chromosome 10 open reading frame 2 (C10orf2) and polymerase gamma 1 (POLG1), which are important for mtDNA maintenance and replication[16]. Here, TYMP is linked to autosomal dominant progressive external ophthalmoplegia.