Through machine learning including the Least Absolute Shrinkage and Selection Operator algorithm, random forest algorithm, and multivariate logistic regression, four key feature genes were obtained-<i>CXCL1</i>, <i>ITGA5</i>, <i>PTX3</i>, and <i>TIMP1</i>-and the diagnostic scores based on these four genes were proved to be effective in distinguishing between AD patients and healthy donors. The gene discussed is PTX3; the disease is Alzheimer disease.