The first thymidine of codon 1002 was changed into a cytosine (CTT>CCT) resulting in a leucine to proline substation at this codon (L1002P) in exon 23 which corresponds to the human L1012P mutation found in patients with mosaic variegated aneuploidy syndrome. A loxP flanked neomycin selection cassette was inserted upstream of exon 23 and was removed via cre-mediated recombination. Western blot confirmed reduced protein expression in mouse embryonic fibroblasts and tissues.