 Expression of these mutant channels results in cells with drastically decreased current density compared to wild-type expressing cells.In cell-based assays, it was found that these mutant channels aggregate in the endoplasmic reticulum, not dissimilar from that seen in the CAG expansion mutants above.R1664Q is in the 4th transmembrane spanning segment of domain 4 and, presumably, affects the channel's voltage dependence of activation.