A prediction of this model is that MCSZ patients in whom the repair of both oxidative SSBs and TOP1‐induced SSBs is defective should exhibit not only neurodevelopmental pathology resulting from unrepaired oxidative SSBs but also neurodegeneration and/or cerebellar ataxia resulting from unrepaired TOP1‐induced SSBs that typifies AOA4 and CMT2B2. The gene discussed is PNKP; the disease is cerebellar ataxia.