Genes That Cause FTD
Genes are segments of DNA that act like “recipes” for producing proteins. Proteins help our body function and keep cells healthy. Variants are changes in the DNA sequence of a gene. Like typos in a recipe, variants may change the instructions for making the protein. In some cases, FTD is caused by genetic variants that alter proteins essential to the normal functioning and survival of brain cells.
Researchers have identified more than a dozen genes that cause FTD, and there are more to be discovered. Three genes cause the majority of genetic FTD – C9orf72, MAPT, and GRN (or progranulin).
C9orf72 — the most common gene associated with genetic FTD and ALS
The genetic variant in the C9orf72 gene is typically a repeated segment of DNA. In most people this segment repeats up to 24 times, which is expected. In people with FTD or ALS, the DNA segment is repeated more than 60 times, leading to a cascade of events that result in an abnormal accumulation of TDP-43 protein in the brain. When a person has a disease-causing expansion of C9orf72, we cannot predict if they will develop FTD, ALS, or both FTD and ALS.
GRN (Progranulin)
The GRN gene provides instructions for making a protein called progranulin, which is involved in cell survival and regulating inflammation. Variants in the GRN gene suppress the production of progranulin. People with GRN variants have abnormal accumulations of TDP-43 protein in the brain. The relationship between GRN variants, decreased levels of progranulin, and abnormal TDP-43 accumulation is not fully understood.
MAPT (Microtubule-associated protein tau)
The MAPT gene provides instructions for making a protein called tau, which helps assemble and stabilize nerve cells in the brain. Variants in MAPT result in abnormal accumulation of tau protein in the brain.
Other FTD-associated genes
Other genes that can cause FTD include VCP, CHMP2B, TARDBP, FUS, SQSTM1, CHCHD10, TBK1, OPTN, CCNF, and TIA1 (Greaves & Rohrer, 2019). Scientists believe there are additional genes that have yet to be identified.
Certain FTD subtypes are associated with variants in specific genes. For example, people diagnosed with FTD-ALS are more likely to have a C9orf72 variant. It is very difficult to predict how FTD will present based on the specific gene identified in the family.
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