Genetic coherence between hereditary amyotrophic lateral sclerosis and frontotemporal dementia

Amyotrophic lateral sclerosis (ALS) has traditionally been considered purely as a motor condition with a progressive loss of upper and lower motor neurons, and without cognitive or behavioural impairment. In 2011 a new genetic mutation that may cause both ALS and frontotemporal dementia (FTD) was detected. In light of this discovery, the article describes genetic and clinical characteristics of ALS and frontotemporal dementia. The article is based on a literature search in PubMed. Up to 50% of ALS patients develop some cognitive impairment, while 3-15% develop frontotemporal dementia. The recently discovered C9ORF72 mutation accounts for 20-50% of hereditary ALS and possibly up to 25% of sporadic cases. The mutation is the most common cause of ALS. Patients with C9ORF72 mutation are characterised by earlier disease onset, reduced survival after diagnosis, more frequent cognitive and behavioural dysfunction, and familial disposition for ALS and frontotemporal dementia. Cognitive and behavioural changes in amyotrophic lateral sclerosis are common, and can appear along a clinical continuum with development of frontotemporal dementia over time. Detection of the C9ORF72 mutation poses a challenge to our knowledge and management of patients with both hereditary and sporadic ALS.