Exon 4 was replaced with one in which a C to T transition resulted in the amino acid substitution of cysteine for arginine at position 170 (R170C), mimicking a mutation associated with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) in humans. A silent mutation creating a HincII site was introduced in exon 4 for genotyping purposes. Cre-mediated recombination removed the floxed neo cassette inserted downstream of exon 5. (J:191454)