HCN2 and multiple system atrophy: Other genes in the region, such as hyperpolarization-activated cyclic nucleotide-gated potassium channel 2 (HCN2), mucosal vascular addressin cell adhesion molecule 1 (MADCAM1), and fibroblast growth factor 22 (FGF22) genes, may also have an etiologic link to MSA, because they exert their functions in the nervous system.