This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics, Subject name: Medicine
DNA topoisomerase 1 autoantibody is specific for? 
Select and explain. 
A. Limited cutaneous systemic sclerosis, B. Mixed connective tissue disease, C. Diffuse scleroderma, D. SLE
C: Diffuse scleroderma
Answer: C: Diffuse scleroderma 
Explanation: Scl-70 antibodies are associated with more severe scleroderma disease. Anti-topoisomerase antibodies can be classified according to their immunoglobulin class (IgM, IgG or IgA). IgG-ATA is found most frequently in scleroderma, with IgA being quite common but IgM very infrequent. Ref Robbins 9/e pg 230