Except there was a catch. In the most common forms of thalassemia, people who show symptoms have mutations in both copies of the related genes. Those born with the most severe forms of thalassemia require transfusions for life to get enough healthy red blood cells, and if the condition is not diagnosed soon enough it can be fatal in early childhood. But Sid’s lab results suggested that only one copy was affected, so he was considered a carrier of the illness, who could pass it on to his children but didn’t have it himself. According to conventional wisdom at the time, carriers were asymptomatic, and compared with someone suffering from the disease’s worst manifestations, he seemed fine.