<prompt> The most common cause of beta thalassemiaMutations leading to aberrant RNA splicing.Mutations lie within the β-globin promoter and lower the rate of β-globin gene transcription.Mutations involve the coding regions of the β-globin geneAll of the above are equally common  <response>: The mutations responsible for β-thalassemia disrupt β-globin synthesis in several different waysMutations leading to aberrant RNA splicing are the most common cause of β-thalassemia. Some of these mutations disrupt the normal RNA splice junctions; as a result, no mature mRNA is made and there is a complete failure of β-globin production, creating β 0 .Other mutations create new splice junctions in abnormal positionswithin an intron, for example. Because the normal splice sites are intact, both normal and abnormal splicing occurs, and some normal β-globin mRNA is made.These alleles are designated β .Some mutations lie within the β-globin promoter and lower the rate of β-globin gene ranscription. Because some normal β-globin is synthesized, these are β alleles.Other mutations involve the coding regions of the β-globin gene, usually with severe consequences. For example, some single-nucleotide changes create termination stop codons that interrupt the translation of β-globin mRNA and completely prevent the synthesis of β-globin. 