The expression of OCT1 variants with reduced activity may lead to the accumulation of toxic metabolites and enhanced exposure to environmental toxins, such as the piperidine derivative 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which may reach the brain and be involved in the development of neurodegenerative diseases [37, 38]. Here, SLC22A1 is linked to neurodegenerative disease.