Cysteine codon 667 (TGC) in exon 4 was changed to phenylalanine (TTC) (p.C667F) and a loxP site flanked neomycin resistance gene cassette was insterted into intron 3. The neo cassette was removed through subsequent Cre-mediated recombination. The mutation is the equivalent of the human c.2006G>T:p.C669F mutation associated with muscle-eye-brain (MEB) disease with multicystic leukodystrophy.