Recombinase mdiated cassette exchange (RMCE) replaced exon 2 with a loxP site, the human cDNA, an FRT-flanked hygro cassette and a loxP site. Flp-mediated recombination removed the hygro cassette. This knock-in lacks the conserved noncoding sequence 28 (CNS28) region contained in Scn5atm1Rdn. Western blot analysis confirmed increased protein expression in the heart compared to in Scn5atm1Rdn homozygotes. (J:185686)