Scientists are beginning to understand the biological and genetic basis for the changes observed in brain cells that lead to frontotemporal dementia, or frontotemporal disorders (FTD).
Scientists describe FTD using the patterns of change in the brain seen in an autopsy after death. These changes include loss of neurons and abnormal amounts, or forms of proteins called tau and TDP-43.
These proteins occur naturally in the body and help cells function properly. When the proteins don’t work properly, for reasons not yet fully understood, neurons in specific brain regions are damaged.
In most cases, the cause of an FTD is unknown. Individuals with a family history of FTD are more likely to develop such a disorder. About 10 to 30% of bvFTD is due to specific genetic causes.
FTD that runs in a family is often related to mutations (permanent changes) in certain genes. Genes are basic units of heredity that tell cells how to make the proteins the body needs to function.
Even small changes in a gene may produce an abnormal protein, which can lead to changes in the brain and, eventually, disease.
Scientists have discovered several different genes that, when mutated, can lead to FTD:
Tau gene (also called the MAPT gene) — A mutation in this gene causes abnormalities in a protein called tau, which then forms tangles inside neurons and ultimately leads to the destruction of brain cells.
Inheriting a mutation in this gene means a person will almost surely develop a frontotemporal disorder, usually bvFTD, but the exact age of onset and symptoms cannot be predicted.
GRN gene — A mutation in this gene can lead to lower production of the protein progranulin, which in turn causes another protein, TDP-43, to go awry in brain cells.
Many frontotemporal disorders can result, though bvFTD is the most common. The GRN gene can cause different symptoms in different family members and cause the disease to begin at different ages.
C9ORF72 gene — An unusual mutation in this gene appears to be the most common genetic abnormality in familial frontotemporal disorders and familial ALS. This mutation can cause a frontotemporal disorder, ALS, or both conditions.
In recent years researchers have discovered several other genetic mutations in genes that lead to rare familial types of frontotemporal disorders. These other mutations account for less than 5% of all cases of FTD.
Families affected by inherited and familial forms of FTD can help scientists advance research by participating in clinical studies and trials.
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