Genetic testing is transforming medicine — and the way families think about their health.

Today gene tests are available for more than 1,300 diseases, including cystic fibrosis and hemophilia. As genetic screening gets cheaper and faster, researchers are hunting down the biological underpinnings of more-complex disorders that involve multiple genes — illnesses that strike millions of Americans every year.

On the list: type 2 diabetes, Alzheimer’s, heart disease and depression. If the scientists are right, genetic tests for some of these diseases could be available by 2010.