A loxP sites flanked second copy of exon 6 with an inserted stop codon, a neomycin resistance gene flanked by loxP sites in intron 5, and an exon 7 with a G to A transition at position 14365 resulting in a glycine to arginine amino acid substitution at position 213 (G213R) mimicking a dominant mutation found in autosomal dominant osteopetrosis type 2 (ADO2) in humans were inserted. The extra exon 6 and the PKG-neo cassette were removed via cre-mediated recombination by mating with Ella-Cre transgenic mice leaving the G213R mutation in exon 7.