Because the syndrome has been identified only recently, it is difficult to ascertain its incidence and distribution in the world. When we analyze the data from the different publications, the disease is responsible for 4 to 12 % of unexpected sudden deaths, and for up to 50% of all sudden death in patients with an apparently normal heart. The incidence may even be higher in the younger population. Indeed, this syndrome is the most common cause of sudden death in individuals younger than 50 in South Asia with no underlying cardiac disease. It is important to stress that the physician plays an important role in the identification of the syndrome to estimate its real prevalence. This syndrome is possibly more prevalent, but the magnitude of it has yet to be determined. The difficulty to estimate the incidence and prevalence of the disease becomes more complicated as we unravel the syndrome and some of its peculiar characteristics. It is a syndrome that can present with a typical electrocardiogram but in some other cases the patient can present concealed forms or intermittent forms, meaning that the electrocardiogram is normal at certain times. The electrocardiogram of the syndrome may be unmasked by the administration of ajmaline, flecainide or procainamide. The pharmacologic test is so specific, that it is recommended in all patients who present with a history of syncope of unknown origin or ventricular fibrillation of unknown cause. Unfortunately, these tests are not applied routinely. Without a doubt this is one of the reasons why the prevalence of the disease probably is underestimated. Recent data from France and Japan show a prevalence of 1 per 1000 electrocardiograms compatible with the syndrome in the normal adult population.

This syndrome has already been recognized in virtually all parts of the world. We suspect that the lack of cases in some countries is due more to the lack of recognition than to the absence of the disease. With present data, the disease seems spread all over the world, a not surprising finding, given the high mobility of the population and the genetic basis of the disease. In the future we only can expect a sizeable increase in the number of identified cases as the recognition of the disease grows.

A prospective study of an adult Japanese population (22.027 subjects) showed an incidence of 0.05% of electrocardiograms compatible with the syndrome (12 subjects). A second study of adults in Awa (Japan) showed an incidence of 0.6 % (66 cases out of 10.420). However, a third study in children from Japan showed an incidence of electrocardiograms compatible with the syndrome of only 0.0006% (1 case in 163.110). These results suggest that the syndrome is manifested during adulthood, which is in accordance to the mean age of the sudden death victims (35 to 40 years). The youngest patient known was 6 months old at the time of sudden death, and the oldest 74.

In the Dutch area of Belgium (6 million inhabitants) already 44 families with the syndrome have been identified. About 15% of members are affected. That gives an incidence of 1:30.000 in that area.