Dr. Hellquist, et al reply

To the Editor: We read with interest the letter of Suarez-Gestal, et al 1, and we believe that it is useful to briefly discuss possible causes of differences between our study2, which reported an interaction between the TYK2 and IRF5 genes, and the report of Suarez-Gestal, et al. It is a common observation that replicating even single-gene association results in complex disorders is not always easy, and largely the same causes that may explain these differences also apply to gene-gene interaction studies. Some of the common causes for the different results include insufficient … Address correspondence to Dr. Hellquist; E-mail: anna.hellquist{at}ki.se