What Is Predictive Testing?

Some medical conditions are caused, partially or entirely, by a mutated gene. People who have a dangerous gene may not be aware of it, but may be aware that it is present in the family. An example is the gene for Huntington's Disease, a debilitating condition that first produces symptoms in middle age. People with a family history of the disease do not know whether they have it until the symptoms arise, but genetic testing can give them this information much more quickly. Assessing whether a person is likely to develop a genetic disease is called predictive testing; along with its benefits, the testing has its drawbacks.

Each person has two sets of genes, one from the mother and one from the father. Occasionally, one of these genes can be mutated in such a way that it produces disease. Both genes may also be mutated into disease-causing forms. In some cases, a mutated gene is not sufficient in itself to cause disease, but can significantly increase the chance of a disease, such as cancer, developing.

Geneticists have sequenced the entire human genome, and have identified many abnormal copies of genes. Research has shown that many diseases have a genetic component, and some are due entirely to genetic mutations. Once a mutated gene can be linked to a medical condition, the presence of the gene in a person's genetic make-up can be used to predict the chance of that person developing the disease.

People undergoing predictive testing have to supply a sample of their genes, from sources like a cheek swab or a blood sample. Then the sample is broken down in the laboratory so an analyst can extract the gene of interest and see if it is normal or mutated. This type of test is offered to people who have not yet shown any indications of disease.

Certain medical conditions are entirely due to mutated genes, such as Huntington's Disease. People who have one copy of the dangerous gene will go on to develop degeneration of the motor and thinking skills of the brain. Other conditions, like cystic fibrosis, require two abnormal genes to be present before medical problems arise. Various other diseases, such as cancer, need several different issues to combine before medical issues develop, but one of the significant factors involved in some cases is inherited genetic mutations.

Generally, only those at high risk of certain diseases are offered predictive testing, due to the cost and the specificity of the tests. For people at risk, an advantage of knowing that they carry the mutated gene is that precautions against disease can be taken. For example, a BRCA1 mutation can put a woman at high risk of breast cancer, so she can invest time and effort in screening or even opt for mastectomy, to reduce the risk.

If a person fears he or she has a dangerous gene mutation, and the test comes back negative, then a lifetime of worry can be lifted. In addition, the person need not worry about passing disease genes onto children. On the other hand, if the predictive testing shows that the person does have the abnormal gene, then he or she may regret this knowledge, especially in cases where the presence of the gene definitively leads to disease. Generally, people thinking about undergoing predictive testing receive genetic counseling, which explains all the options along with the potential repercussions of the decision.