Sudden Unexplained Death Syndrome (SUDS)(or Lai-tai) is sudden death in previously healthy young adults without any structural cause of death from autopsy findings. Our previous data showed that familial SUDS is not X-linked recessive. The objective of this study was to determine the pattern of inheritance in familial SUDS using the ECG markers of Brugada syndrome (RBBB and ST-segment elevation in V1 to V3), SUDS and presumptive SUDS as phenotypes. We employed the standard 12-lead ECG and higher intercostal space (ICS) V1 to V3 (-V1 to-V3 and-2V1 to-2V3) leads ECG in SUDS relatives after procainamide and drew the pedigree. We studied 62 relatives of 9 SUDS victims who died in Singapore and selected 3 families (n= 34) for the procainamide test and ECG. The mean age was 36.4+/-23.6 years (4-78 years). Three SUDS families showed the same pattern of inheritance of autosomal dominant.