More than 4,000 diseases are thought to be related to mutated genes that are inherited from one or both parents. But whether a gene actually triggers a disease can be dependent on a variety of factors, including lifestyle and the environment. Genetic testing can determine if a person has a predisposition to a particular condition. Many doctors now offer genetic tests for cancers that run in families, including a test for the BRCA1 gene mutation that predisposes women to hereditary breast and ovarian cancer, as well as tests for colon cancer an ....