 A specific gene in mouse brain thought to be involved in the onset of Alzheimer's disease which codes for the enzyme cyclin-dependent kinase 5 (Cdk5) was knocked out.Such mice were found to be 'smarter' than normal mice and were able to handle complex tasks more intelligently compared to 'normal' mice bred in the laboratory.Conditional gene knockouts in mice are often used to study human diseases because many genes produce similar phenotypes in both species.