Unexpected syncope and death during intense physical training: evolving role of molecular genetics

Special operations forces (SOF) undergo an unparalleled degree of physical training. The medical officer responsible for these personnel must often deal with episodes of syncope that cannot be readily explained. In the past, loss of consciousness during heavy physical exertion was attributed to inadequate fluid intake resulting in dehydration or abnormalities in temperature regulation. However, many of those diagnoses, in retrospect were probably incorrect. The occurrence of exercise-related syncope in multiple members of the same family suggested that there could be a genetic basis for the unexpected loss of consciousness during exercise. Intensive clinical examinations of these patients, coupled with current advances in molecular genetics, have shown this to be the case. We review some of the more common genetic abnormalities associated with exertion-related syncope. These syndromes should be considered by the medical officer presented with a patient having syncope of indeterminate cause.