According to the passage, ____ could be a risk factor in the development of Alzheimer’s disease.
Scientists have shown that people who have a variant of a longevity gene, called KLOTHO, have improved brain skills such as thinking, learning and memory, regardless of their age, sex, or whether they have a genetic risk factor for Alzheimer’s disease. Increasing KLOTHO gene levels in mice made them smarter, possibly by increasing the strength of connections between nerve cells in the brain. The study was partly funded by the National Institutes of Health.