Aspartic acid codon 620 (GAT) in exon 15 was changed to asparagine (AAT) (p.D620N) and a loxP site flanked neomycin resistance gene cassette was inserted into intron 15. The neo cassette was removed through subsequent Cre-mediated recombination. The equivalent human mutation is found in some familial type 17 Parkinsonâs disease (PARK17) patients.