αENaC-associated splice variants and mutations identified in human (h), rat (r), and chicken (c). The αENaC contains 2 transmembrane domains (TMs), 2 cysteine-rich domains (CRDs), a leucine-rich domain (LRD), and a pore-forming region (P) just before TM2. The human αENaC2+59 contains an additional 59 amino acids at the NH₂-terminus (14). Three human αENaC splice variants (hαENaC C229x, hαENaC-19, and hαENaC+22) cause loss of function in Xenopus oocytes (3). The hαENaC+Alu contains an Alu fragment at the CRD2 (Y.S. Oh and D.G. Warnock, unpublished data). Two αENaC splice variants (αENaCax and αENaCbx) were identified in rat taste tissue (15), and αENaCx was identified in chicken cochlea (16); these splice variants, as well as hαENaC+22 and hαENaC+Alu, use the same splice site in the CRD2 exon (3). Four human αENaC mutations (G37S, I68x, C133Y, and R508x) have been identified in PHA-I individuals (6, 7). Here, “x” denotes a prematurely truncated protein, whether the new stop codon is generated by point mutation or frameshift.