Here, we will examine those classic toxic biomarkers that have been used to define AD (Aβ, pTau), ALS (pTau, TDP-43, FUS, SOD1), FTD (pTau, TDP-43, FUS, SOD1), HD (mHtt), and PD (αSyn), before covering their importance in mixed pathologies associated with each NDD. The gene discussed is SOD1; the disease is Huntington disease.