Previous studies revealed a linkage of the kainate receptor GluR6 with autism. Mutational screening in autistic patients disclosed the amino acid exchange M836I in GluR6. Here, we show that this mutation leads to GluR6 gain-of-function. Western blotting of oocytes and transfection into COS-7 cells revealed an enhanced plasma membrane expression of GluR6(M836I) compared to wild type GluR6. Membrane expression of GluR6(M836I) but not of wild type GluR6 seems to be regulated by Rab11 as indicated by our finding that GluR6(M836I) but not wild type GluR6 showed increased current amplitudes and protein expression when coexpressed with Rab11. By contrast, Rab5 downregulated the currents in oocytes expressing wild type GluR6 but had only little effects on currents in oocytes expressing GluR6(M836I). Our data on altered functional properties of GluR6(M836I) provide a functional basis for the postulated linkage of GluR6 to autism. Furthermore, we identified new mechanisms determining the plasma membrane abundance of wild type GluR6 and GluR6(M836I).