SLC26A9 and cystic fibrosis: In contrast, the NHE3 gene (encoding the NHE3 Na+/H+ exchanger functionally coupled to SLC26A3) and the evolutionarily related SLC26A9 gene (highly expressed in apical membrane of mouse stomach and duodenum, Liu et al., 2015) were detected as CF meconium ileus modifier genes (Sun et al., 2012).