Beta-Thalassemia Is a Disease That Results from the Reduction or Absence

Beta-thalassemia is a disease that results from the reduction or absence of a functional $\beta$ -globin gene.It results in patients that exhibit moderate to severe anemia,poor growth,and possibly skeletal abnormalities.Depending on how severe a patient presents,they may need regular to periodic blood transfusions throughout their life.It is known that there are various mechanisms of mutation that result in beta-thalassemia.You are studying a group of individuals with beta-thalassemia in order to better understand the disease.Upon sequencing the $\beta$ -globin gene,you notice that only about half of the patients in your study have deletions in their $\beta$ -globin gene.The other half has no abnormalities in the sequence of this gene.From other tests,you know that these patients do in fact have beta-thalassemia,as they are deficient in $\beta$ -globin protein and other members of their families also suffer from similar conditions.What is the most likely explanation for the presence of this genetic disease in these people?

A) There is a mutation in the promoter of the $\beta$ -globin gene preventing adequate expression of the protein.
B) There was an inversion with a splice point within the $\beta$ -globin gene.
C) There is a microorganism,such as a virus,that is causing these symptoms.
D) The patients actually have bone marrow cancer that is causing these symptoms.
E) The patients actually have sickle-cell anemia.