Actually, these deaths are also frequent in East Asian men who stay in their country, only in most cases the autopsy report lists the death as unexplained or natural cause. Also, the Hmong people do not normally perform autopsies because it goes against their beliefs, so there's a bunch of unreported cases of death by SUNDS.
As for the studies, several have been conducted and in most cases there is indeed a genetic defect that causes Brugada syndrome, or long Q-T syndrome. However, a small percentage of the subjects (around 5%) do not show any genetic predisposition for heart diseases.
Thanks for the detailed answer! As for many disease, having a proper diagnostic is thus crucial to understand better.
Indeed, that, and good epidemiological records to better understand the disease and its causes.
This is also why some diseases seem more likely happening those days. In fact, they are just better diagnosed.