This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diabetes Mellitus, Subject name: Medicine
Which gene is involved in pathogenesis of Type 1 Diabetes mellitus? 
Select and explain. 
A. CTLA-4, B. ABCD1, C. HNF-1 Alpha, D. HNF-4 Alpha
A: CTLA-4
Answer: A: CTLA-4 
Explanation: Polymorphism in promoter region of insulin gene, CTLA-4 contributes to susceptibility to type 1 Diabetes mellitus. The most common cause of type 1 diabetes mellitus is autoimmunity. Most patients have DR3 and/ or DR4 haplotype.