Exon 3 was replaced with a floxed neo cassette and a modified exon 3 in which a silent mutation inserted a SacI site and a nucleotide substitutions (CGC to CAG) results in the amino acid substitution of glutamine for arginine at position 176 (R176Q), mimicking a mutation found in some autosomal dominant hypophosphatemic rickets (ADHR) patients. Cre-mediated recombination removed the neo cassette.