For many variants, however, previous findings were inconclusive and based on our current discoveries we speculate that some of the seemingly conflicting results are due to differences in the composition (and size) of study cohorts, most importantly: (1) the number of patients with predominant FTD, predominant MND or a mixture of both diseases, (2) the percentage of subjects with a pathologically confirmed diagnosis, and (3) the subset of individuals with pathogenic mutations in particular FTD and/or MND-associated genes (such as C9ORF72). This evidence concerns the gene C9orf72 and frontotemporal dementia.