MTH1 (human MutT Homolog 1) is an oxidized purine nucleoside triphosphatase enzyme that belongs to the Nudix hydrolase family and it acts as major mammalian detoxifier of the oxidized DNA precursor, 8-oxo-dGTP thereby exerting antimutagenic effects and suppressing cell dysfunction/death induced by oxidative stress. MTH1 hydrolyzes 8-oxo-dGTP, 8-oxo-dATP and 2-OH-dATP, thereby preventing misincorporation of oxidized purine nucleoside triphosphates into DNA and subsequently preventing A:T to C:G and G:C to T:A transversions. MTH1 also hydrolyzes the corresponding ribonucleotides, 2-OH-ATP, 8-oxo-GTP and 8-oxo-ATP. 2-OH-dADP, 8-OH-dGDP and 8-OH-dGTP inhibit the 2-OH-dATPase activity whereas 8-OH-dGTPase activity is inhibited by 8-OH-dGDP, 2-OH-dADP and 2-OH-dATP. Localized mainly in the cytoplasm, MTH1 has been found in nucleus and mitochondria also, and is widely expressed with highest expression in thymus, testis, embryo, proliferating blood lymphocytes etc. Oxidative DNA damage, e.g. 8-oxoG is known to accumulate both in nuclear and mitochondrial genomes during aging, carcinogenesis or various neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease or amyotrophic lateral sclerosis and MTH1 deficiency can increase susceptibility to these oxidative damage mediated dysfunctions.