Tyrosyl-DNA phosphodiesterase (TDP1) is a DNA repair enzyme that catalyzes the hydrolysis of a phophodiester bond between a tyrosine residue and a DNA 3' phosphate. This protein is a member of the phospholipase D (PLD) superfamily and contains two PLD phosphodiesterase domains. Mutations in TDP1 are associated with the disease spino-cerebellar ataxia with axonal neuropathy (SCAN1) by interfering with DNA transcription or by inducting apoptosis in postmitotic neurons.