on a common haplotype in 9p21.2 linked families with ALS and FTD [15], [16], [47] thus illustrates the potential of the combined use of gene expression and genotyping in search for causative genes in human diseases. The mechanism though of the recently discovered repeat expansion in C9orf72 remains to be established. There could be a direct effect of expression levels of isoforms of C9orf72, or a “trans”-like effect through RNA-toxicity, as shown in other repeat expansions diseases including fragile X-associated tremor/ataxia syndrome (FXTAS) [48]. Other types of experiments are needed to elucidate this mechanism.
