Genetic etiology of Fronto-Temporal Dementia, a dementia related to Alzheimer's disease

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Amyotrophic lateral sclerosis (ALS; Lou Gehrig's disease) is a fatal neurodegenerative disorder that leads to rapidly progressive paralysis and respiratory failure. ALS is the third most common neurodegenerative disease in the Western World, and there are currently no effective therapies. Frontotemporal dementia (FTD) is the most common form of dementia in the population under the age of 65. Frontotemporal dementia is part of the "Alzheimer's disease and related dementias" spectrum of illness. Overlap between these two clinically distinct neurological diseases has long been recognized, but the molecular basis of this intersection was unknown. In 2011, the Neuromuscular Diseases Research Section (NDRS), a part of the Laboratory of Neurogenetics at the National Institute on Aging, identified the major genetic cause of both ALS and FTD. To do this, Dr. Traynor (chief of NDRU) organized a worldwide consortium, bringing together groups that had previously been competitors to focus their efforts on identifying this gene. This was made possible by the next-generation sequencing technologies available at the NIH. This innovative approach worked, and his group published the cause of chromosome 9-linked ALS/FTD in the journal Neuron in September 2011. In these cases, the disease is caused by a six-base pair segment of DNA that is pathologically repeated over and over again, up to several thousand times. This so-called large hexanucleotide repeat disrupts the C9ORF72 gene located on chromosome 9. This is the most common genetic cause of both ALS and FTD identified to date, accounting for approximately 40% of all familial cases of ALS and FTD in European and North American populations. Further, Dr. Traynor's group has shown that this mutation underlies about 8% of cases of sporadically occurring ALS and FTD that lack a family history. This represents the first time that a common genetic cause has been identified for the sporadic form of these diseases. In a separate publication in The New England Journal of Medicine, they have also shown that the same large hexanucleotide repeat expansion underlies 1% of patients clinically diagnosed with Alzheimer's disease. A one percent reduction in the number of AD cases would represent approximately $1 billion in healthcare cost savings annually. The discovery of the C9ORF72 hexanucleotide repeat expansion is a landmark discovery in our understanding of neurodegenerative diseases. It has already greatly affected how these diseases are diagnosed, investigated and perceived, and provides a mechanistic link between two clinically distinct disorders, ALS and FTD. It also provides a distinct therapeutic target for gene therapy efforts aimed at ameliorating the disease, and such efforts are already well underway. In 2021, we published a paper describing the analysis of whole-genome sequence data for a large cohort of FTD/ALS patients in which we found the HTT repeat expansion to be a rare cause of these diseases. In 2022, we published a review describing the genetic overlap between ALS and FTD. We also published a paper describing mutations in KIF5A as a cause of FTD. In 2023, we published a paper describing the structural variant analysis for a large cohort of FTD/ALS patients. In summary, we have been successful in identifying genetic variants important in the pathogenesis of FTD using next-generation sequencing. Our data also helps to unify FTD and ALS into a single disease rubric that encompasses two of the major late-onset neurodegenerative diseases.