Comments from the observers of the study propose phenotyping error as the cause of the extreme phenotype difference. The more sensitive sibling felt nauseated during the challenge. This is a common response reported by many subjects, and the SHAS score for this individual is around the same value reported by other individuals with a similar response. The other sibling, with SHAS scores indicating they were insensitive to alcohol, had a blood alcohol level close to the predicted value, indicating that they were appropriately dosed. This sibling fainted briefly during blood draw. The researchers involved in testing these subjects take special care to avoid fainting and report that it only happens 2% of the time. Although the subject woke up quickly and admittedly felt fine, this fainting spell could have contributed to the low response indicated by a low SHAS score. Therefore it is likely that the reduction in LOD score by the inclusion of the discordant family is due to a phenotyping error. While the inclusion of this family has dramatic affect on the linkage analysis it has a negligible
