The most frequent mutation in Hutchinson-Gilford progeria syndrome, a C to T change, was introduced into exon 11. This mutation does not result in a protein sequence change because both encode a glycine at amino acid position 609 (G609G). In addition, a loxP flanked neomycin resistance gene was introduced upstream of exon 11. Cre-mediated recombination removed the neomycin resistance gene. The G609G is equivalent to the human G608G mutation which activates an alternate splicing event and generates a 50-amino acid truncated form of Lamin A, referred to as progerin.