Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes loss of motor neurons. A pathological hallmark of ALS is the presence of ubiquitinated TAR DNA binding protein (TDP-43) inclusions in the cytoplasm of affected cells. Rare pathogenic mutations within the gene TARDBP that encode TDP-43 were recently reported in ALS but their functional consequences are unknown. To further investigate the pathogenic role of TDP-43 in ALS, a mutation analysis of TARDBP was performed in an Australian cohort of 74 sporadic and 30 familial ALS cases. A novel familial ALS mutation in TDP-43 was identified that substitutes a highly conserved residue (G294V) and is predicted to disrupt the glycine rich domain in the C terminus, a region that plays a role in RNA binding and is required for the exon skipping activity of TDP-43.