History
Laotian Hmongs were chosen for the study because they had one of the highest sudden death rates in the United States while sleeping. They were originally from Southern China and the highlands of North Vietnam, Laos, and Thailand. The location that was picked for this study was in Ban Vinai in the Loei Province, which is approximately 15 kilometers from the Lao border. This study took place between October 1982 and June 1983 as this syndrome became more of a pressing issue. Ban Vinai was the location chosen because it had 33,000 refugees in 1982, and the largest number of recorded SADS deaths. Because this syndrome was occurring most commonly in those particular men, researchers found it most beneficial and effective to study the populations they migrated from instead of studying victims and populations in the U.S. Because of local religious practices, the Hmong men in Ban Vinai did not receive autopsies. Therefore, the only results and research obtained were relating to deaths outside of the local religion or geographical area.An interview was arranged with the next of kin who lived with them, witnessed the death, or found the body. The interviews were open ended and allowed the person who was next of kin to describe what they witnessed and what preceding events they thought were relevant to the victims death. The interviewers also collected information such as illness history, the circumstances of the death, demographic background, and history of any sleep disturbances.
By 1981–1982, the annual rate in the United States was high with 92/100,000 among Laotians-Hmong, 82/100,000 among other Laotian ethnic groups, and 59/100,000 among Cambodians.In a 2008 study it was found that over half of SADS deaths could be attributed to inherited heart disease: unexplained premature sudden deaths in family, long QT syndrome, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy and others.A national SADS study in England, funded by the British Heart Foundation, reported results in a 2007 journal article published in Health. The study surveyed 117 coroners jurisdictions in England. Researchers found that deaths from SADS reported by these coroners occurred "predominantly in young males". There were 500 cases a year in England, which is 8 times more than was previously estimated. Families are more at risk of SADS if they have a genetic cardiac disease. The study recommended that affected families should undergo "specialised cardiological evaluation". Asia
Southeast Asian immigrants, who were mostly fleeing the Vietnam War, most often had this syndrome, marking Southeast Asia as the area containing the most people with this fatal syndrome. There are other Asian populations that were affected, such as Filipinos and Chinese Filipinos, Japanese in Japan, and natives of Guam in the United States and Guam. The immigrants with  this syndrome were about 33 years old and seemingly healthy, and all but one of the Laotian Hmong refugees were men. The condition appears to primarily affect young Hmong men from Laos (median age 33) and Northeastern Thailand (where the population is mainly of Laotian descent).