Beginning in 1985, patients and their unaffected relatives were longitudinally followed in this multicenter study to develop and validate widely applicable clinical criteria for stratifying the risk of life-threatening arrhythmias. A population of genetically deaf students was surveyed to identify additional families with the unique association of Long QT Syndrome and congenital deafness in order to expand the data base for genetic studies in the recessive form of the disorder, the Jervell and Lange-Nielsen Syndrome. Pedigrees of selected Long QT Syndrome families were recorded to better understand the inheritance of the dominant form of the disorder, the Romano-Ward Syndrome. Genetic studies were conducted using human leukocyte antigen and other protein markers in order to investigate the gene locus for the autosomal dominant form of the syndrome. A select group of 30 patients and 30 unaffected relatives had 24-hour Holter monitoring, treadmill exercise, Valsalva maneuver and handgrip stress tests to determine if the patients had a unique cardiovascular response to autonomic dysfunction.