<prompt> Hemoglobin H disease is caused by deletionSingle a globin chainTwo a globin chainsThree a globin chainsAll a globin chain  <response>: Ans. c Three a globin chainsRef: Robbins 9thpg 638Classification of a-thalassemia:Normally 4 a-genes synthesize: 2 a chains - a, a a, aMost common cause of a -thalassemia is a -gene deletion frame-shift mutation9 