Exon 10 and 11 were replaced with a floxed neo cassette and another copy of exon 10 and 11 with a nucleotide transition of G to A at position 1449 within exon 11. This transition results in an amino acid substitution of a histidine for an arginine at position 439 (R439H). The neo cassette was removed by transient cre-mediated recombination in ES cells. This allele was created to mimic the R441H mutation identified in humans that leads to 80% reduced enzymatic activity in PC12 cells.