Letter: allopurinol co‐therapy is safe and effective in autoimmune hepatitis – authors' reply. Issue 9 (3rd April 2013) - de Boer, Y. S.; van Gerven, N. M. F.; de Boer, N. K. H.; Mulder, C. J. J.; Bouma, G.; van Nieuwkerk, C. M. J.