<prompt> A 4-year-old boy has a chronic microcytic anemia, but no other symptoms. His physical examination is normal except for splenomegaly. His condition is due to decreased alpha-chain production, which leads to four beta-chain tetramer formation HbH.For the above patient with a hemoglobin abnormality, select the most likely diagnosis.beta-thalassemia majorHbH diseasesickle cell diseaseHbC disease  <response>: HbH four beta-chains most commonly results from the compound heterozygous state for alpha thalassemia --a. The phenotypic expression of the disease is quite variable. 