First the patient is found to have a syndrome, which is a collection of symptoms that seem to occur at the same time. Once the syndrome has been identified, the etiological phase begins, where a search for a cause begins. The four causes possible causes listed above are then considered. Once etiology is established then a way of preventing the illness, especially if it appears to be untreatable, or methods of treatment for those who already have the illness are then sought out. In the past century there has been a huge advancement in genetic studies.
Scientists can now approximate the common genes between family members of varrying closeness.
A researcher can then look at the family members of a patient diagnosed with a mental illness and look for other family members who show signs of the same mental illness. When it is found that members of the same family tend to have a certain disease, other factors being equal, then a hereditary influence is suggested. Higher concordance rates than that of fraternal twins provides a strong argument for an hereditary effect on that illness. When identical twins are separated by adoption, their environmental factors are different so the only thing that would most likely cause the same illness in both would be heredity. When the concordance rate is still found to be high in these studies, an even stronger argument for hereditary influence is built.