Original: DNA testing on the remains of the royal family proved conclusively in 2009 that Alexei suffered from Hemophilia B , a rarer form of the disease . His mother and one of his sisters , identified by the Russians as Anastasia and by Americans as Maria , were carriers .
Simplified: DNA testing on the remains of the royal family proved in 2009 that Alexei suffered from Hemophilia B. His mother and one of his sisters were carriers .