Isogenic controls also have the power to show that some cellular phenotypes are dependent on genetic background even in monogenetic conditions; correction of LRRK2 variants in another study exposed both LRRK2-dependent and LRRK2-independent effects, which were likely related to genetic background and reflected the heterogeneous clinical features and variable severity in familial PD (Nickels et al., 2019). This evidence concerns the gene LRRK2 and Parkinson disease.