TDP1 and spinocerebellar ataxia, autosomal recessive, with axonal neuropathy 1: The importance of Tdp1 in humans is highlighted by the observation that a recessive mutation in the TDP1 is responsible for the inherited disorder, spinocerebellar ataxia with axonal neuropathy (SCAN1) [15,20] in which a H493R mutation in the Tdp1 causes the accumulation of both Top1-DNA and Tdp1-DNA covalent intermediates in vivo[13,21–23].