3' targeting vector containing a loxP site was inserted downstream of exon 79. Subsequently 5' targeting vector containing second loxP site was inserted to replace brain-type promoter and its specific exon 1. In resulting mutant animals, the entire region of the Dmd gene was flanked by two loxP sites, and full-length expression in the brain was specifically inactivated. RT-PCR and Western blot analyses showed full length dystrophin expression in the cerebrum was specifically inactivated, with no effect on expressions of other isoforms. (J:96210)