Stanford Cardiac Arrhythmia Service

Hereditary Conditions and Aging

Genes contain the instructions for the building blocks of cells, which come together to create living beings.  Small differences in genes are what result in the variation between one person and another.  However, some genes with rare variations, or mutations, can result in abnormally working building blocks which can then lead to medical illness.  In the case of arrhythmias, there are mutations in ion channels, which are proteins, or building blocks, in the heart cells responsible for healthy flow of electrical signals that control the heart beat. 

Depending on the specific ion channel involved, different mutations can lead to different types of arrhythmias, some of which may increase the risk of dangerously fast heart rhythms.    The long QT syndrome, for example, can be caused by a mutation in one of over ten genes that have been identified. The vast majority of the genes involved are potassium and sodium channels.  Most of the genetic mutations are inherited in a dominant manner, meaning that only one copy of the mutation from one parent is sufficient to cause the disease. However, in a small percentage of patients, the disease is inherited in a recessive manner, meaning that the patient must have two copies of the mutation, one mutation inherited from each parent.

There are currently commercially available genetic tests to identify mutations for several arrhythmic conditions such as long QT Syndrome, Brugada Syndrome, Arrhythmogenic Right Ventricular Cardiomyopathy.  However, the interpretation of these genetic tests is not black and white.  Current genetic testing only identifies the culprit mutations in a certain percentage of patients, depending on the disease in question. This means that a genetic test that is “negative” does not completely exclude the disease. In addition, there are patients with genetic mutations who never develop disease, meaning that a “positive” test does not automatically signify that a person will develop the disease. Some mutations are more severe than others, and knowing which mutation one has may help with the management of the patient, although much degree of personalized medicine is still experimental.

Genetic testing is most useful when one member of a family has been clinically diagnosed with an arrhythmia. If the mutation causing the disease in that person is identified, then the family members can be tested for the disease with genetic screening. We recommend genetic counseling before genetic tests are ordered to discuss the implications of the testing itself and the potential results as well as the effects on the individual and the rest of the family.

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