A targeting vector was designed to insert an exon 15 with the G to A mutation at position 2531 coding for the glycine to aspartate substitution at amino acid 844 (G844D) and a puromycin resistance gene flanked by FRT sites in intron 15. The selection maker was removed via Flp-mediated recombination. This is equivalent to the most commonly found mutant allele (G843D) in patients with Zellweger spectrum disorder.