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 spinocerebellar ataxia with axonal neuropathy (SCAN1) by interfering with DNA transcription or by inducting apoptosis in postmitotic neurons.