Exon 1 was replaced with an exon 1 containing a 27 bp duplication (9 amino acid duplication of ALLLLCALL) in the signal peptide followed by a floxed neomycin cassette. The neomycin cassette was removed via flp-mediated recombination. This duplication has been identified in patients with early onset familial Pagets disease of bone. (J:312215)