A loxP site was inserted upstream of exon 7. An inverted modified exon 7 with a nucleotide substitutions that result in the amino acid substitution of cysteine for tyrosine at position 279 (Y279C) with a 5' loxP site was flanked by loxP511 sites and inserted downstream of exon 7 along with an FRT flanked neo cassette. Flp-mediated recombination removed the neo cassette, and cre-mediated recombination removed the endogenous exon 7 and reverted the orientation of the modified exon 7. The amino acid substitution is one of the two most common mutations in Leopard syndrome.