Inosine Triphosphate Pyrophosphatase (ITPase) is a cytoplasmic enzyme that belongs to the HAM1 NTPase family. ITPase hydrolyzes the non-canonical purine nucleotides inosine triphosphate (ITP) and deoxyinosine triphosphate (dITP) to the monophosphate nucleotide (IMP) and diphosphate. The ITPase enzyme acts as a homodimer and does not distinguish between the deoxy- and ribose forms. ITPase probably excludes non-canonical purines from RNA and DNA precursor pools, thus preventing their incorporation into RNA and DNA and avoiding chromosomal lesions. Defects in ITPase is thought to be inherited and is characterized by an over-accumulation of ITP in erythocytes, leukocytes and fibroblasts.