PMP22 and amyotrophic lateral sclerosis: Genetic susceptibility has been reported by association studies that revealed also several potential ALS risk genes such as Solute Carrier Organic Anion Transporter Family Member 1B1 (SLCO1B1), Thiopurine S-Methyltransferase (TPMT), and Peripheral Myelin Protein 22 (PMP22) [9].