After Alzheimer's, frontotemporal dementia is the most prevalent form of dementia in patients younger than 65. FTD affects the frontal lobe, causing the brain tissue to die off. The frontal lobe is the foremost part of the brain and accounts for about 30% of the brain's mass. Among other things, the frontal lobe is involved in regulating behavior, movement and mood, and is responsible for cognitive functions like memory and speech. So, FTD is clinically characterized by changes in personality and, in a later stage, loss of cognitive functions.
Looking for the needle in the haystack
Genetic research has previously shown that FTD is caused by a defect in chromosome 17. Chromosome 17 is the carrier of the tau protein's hereditary code, and defects in this protein cause tau-positive FTD. However, there is another form of FTD that occurs much more frequently than tau-positive FTD − namely, ubiquitin-positive FTD (FTDU). Patients with FTDU do not have a defect in the tau protein, but in another protein in chromosome 17. Christine Van Broeckhoven's research team has now identified this protein: progranulin. In order to substantiate this discovery, the group worked intensively with neurologists from university memory clinics in Antwerp, Leuven, and Ghent. Genetic analyses of the DNA from FTDU families identifies defects that cause a shortage of progranulin. Progranulin is known in cancer research, where a surplus of this protein leads to tumors. What it does in the brain, and how it supports brain cells, is not yet known.
An unexpected turn
The biological role of progranulin in the formation of FTD provides a totally new insight into how brain cells die off. Van Broeckhoven's team's research indicates that the quantity of progranulin in the brain is important for the brain cells' survival. The hereditary defects that the researchers have found in FTD patients cause only 50% of the protein to be produced, because only one copy of the gene is active. Therefore, FTD patients produce less progranulin than healthy individuals. It has already been shown that too much progranulin leads to cancer − now, these researchers are revealing that too little progranulin underlies FTD.
New diagnostic and therapeutic possibilities
This discovery does not directly result in a new remedy for FTD patients − a lot more research is needed for that. But this finding does offer the prospect of a new treatment for FTD and possibly also for other diseases of the brain that entail the dying off of brain cells − like Alzheimer's disease as well as Parkinson's disease. Given that a deficiency of progranulin leads to FTD, administration of this protein could offer a simple solution. However, the trick will be to administer the right quantity, because too much progranulin leads to the formation of tumors. A fine line to navigate! Thanks to this finding, though, upon a doctor's request, a genetic study can be done on FTD patients and their family members if they so desire.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
Published on PsychCentral.com. All rights reserved.