To test whether App, Il1-r1 and Sod1 contribute to the naturally occurring variation in inbred lines of mice we used a heterogenous stock (HS) of mice inoculated with the Chandler/Rocky Mountain Laboratory (RML) mouse-adapted scrapie prion strain to look for a statistical association between prion disease incubation time and these genetic loci [22]–[25]. Here, SOD1 is linked to scrapie.