Genetic testing is a term that encompasses a wide range of possibilities that apply to a wide range of clinical situations. Some genetic tests involve diagnosing a chromosomal abnormality (like Downs' syndrome) during pregnancy. Other genetic tests are done in children or adults when there is a concern about diagnosing a disease that is directly heritable. There are many different kinds of disease that can be identified on a genetic evaluation.
However, what is also important to remember is that the vast majority of disease are NOT caused by a single gene. In fact, the most common health problems--heart disease, high blood pressure
, diabetes, most cancers--are caused by many factors, including a genetic influence (but not a single gene that can be tested for), lifestyle choices, and environmental factors.
Genetic testing is only initiated when there is a particular disease that a patient may have based on his or her clinical exam or when there is a known disease that runs in the family for which there is a benefit in early diagnosis. For example, in a family in which multiple people have been diagnosed with early breast cancer, a woman may want to know if she has the BRCA gene that is associated with breast cancer.
If you are concerned that you might have 'some crazy diseases' then the best thing to do is see a primary care physician
who can do a thorough personal history, family history, and physical exam to see if your symptoms suggest anything for which genetic testing might be a good option.