Exon 3 was replaced with a floxed neo cassette and a modified exon 3 in which a nucleotide substitutions (c.G2723A and a silent mutation generating a novel and unique Sal1 restriction site to facilitate genotyping) result in the amino acid substitution of histidine for arginine at position 132 (R132H), mimicking a mutation found in human patients suffering from leucoencephalopathy with vanishing white matter. (J:179801)