Co-Occurrence of the C9ORF72 Expansion and a Novel GRN Mutation in a Family with Alternative Expression of Frontotemporal Dementia and Amyotrophic Lateral Sclerosis.

The C9ORF72 repeat expansion is the major cause of frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS), and FTLD-ALS. In the reported pedigree, the 47-year old proband, presenting a four-year history of frontotemporal dementia, carried the C9ORF72 expansion plus a novel GRN p.Cys246X mutation. The father and a paternal uncle, harboring the C9ORF72 expansion only, had died by pure ALS with onset at 63 and 76 years, respectively. The case report and a review of the literature emphasize that phenotypical variations of the FTLD-ALS spectrum could be due to digenic inheritance.