This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'The most common cause of beta thalassemia \nSelect and explain. \nA. Mutations  leading  to  aberrant  RNA  splicing., B. Mutations  lie  within  the  β-globin  promoter  and lower  the  rate  of  β-globin  gene  transcription., C. Mutations  involve  the  coding  regions  of  the  β-globin  gene, D. All of the above are equally common', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The\xa0 mutations\xa0 responsible\xa0 for\xa0 β-thalassemia\xa0 disrupt β-globin synthesis in several different ways\nMutations\xa0 leading\xa0 to\xa0 aberrant\xa0 RNA\xa0 splicing\xa0 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\xa0 complete\xa0 failure\xa0 of\xa0 β-globin\xa0 production,\xa0 creating\xa0 β 0 .\nOther mutations create new splice junctions in abnormal positions—within\xa0 an\xa0 intron,\xa0 for\xa0 example.\xa0 Because\xa0 the normal splice sites are intact, both normal and abnormal splicing occurs, and some normal β-globin mRNA is made.\n\nThese alleles are designated β + .\n\nSome\xa0 mutations\xa0 lie\xa0 within\xa0 the\xa0 β-globin\xa0 promoter\xa0 and lower\xa0 the\xa0 rate\xa0 of\xa0 β-globin\xa0 gene\xa0 ranscription.\xa0 Because some normal β-globin is synthesized, these are β +\xa0 alleles.\nOther\xa0 mutations\xa0 involve\xa0 the\xa0 coding\xa0 regions\xa0 of\xa0 the\xa0 β-globin\xa0 gene,\xa0 usually\xa0 with\xa0 severe\xa0 consequences.\xa0 For example, some single-nucleotide changes create termination\xa0 (“stop”)\xa0 codons\xa0 that\xa0 interrupt\xa0 the\xa0 translation\xa0 of β-globin mRNA and completely prevent the synthesis of β-globin.', 'role': 'assistant'}]