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Study uses mice and brains from deceased Alzheimer’s patients to assess BRCA1 involvement


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Researchers noted reduced levels of BRCA1 protein in the brains of mice and deceased Alzheimer's patients. While this study is interesting early work on the biology of Alzheimer's disease, the focus was primarily Alzheimer's disease, rather than the effect of BRCA1 mutations on Alzheimer's. Therefore, this study's observation may be something that is seen in Alzheimer's patients, but does not necessarily cause the disease. No studies suggest that BRCA1 mutation carriers are at increased risk for Alzheimer's disease.


STUDY AT A GLANCE

This study is about: 

A potential role for normal BRCA1 protein in Alzheimer’s disease.

Why is this study important?

This study is basic research on Alzheimer’s disease.

Study findings: 

  1. Mice that do not have BRCA1 protein in their neurons had more DNA damage, smaller neurons, and deficiencies in learning and memory.
  2. Brains from deceased patients with  Alzheimer’s disease had less normal BRCA1 protein than brains of people without Alzheimer’s.

What does this mean for me?

Currently, no association has been found between BRCA1 mutations and Alzheimer’s disease. While this study provided an interesting laboratory finding—reduced levels of BRCA1 protein in the brains of deceased Alzheimer’s patients—the results are not clinically relevant to people with BRCA mutations. Alzheimer’s disease is complex, and many things go wrong biologically. This study did not show that reduced BRCA1 protein levels cause Alzheimer’s disease, but it did raise the question of whether reduced levels is one of the changes that occur in someone who has Alzheimer’s disease.

This study does NOT show that you have an increased risk of Alzheimer’s if you have a BRCA1 mutation.

Questions to ask your health care provider:

  • What are known risk factors for Alzheimer’s? 

IN DEPTH REVIEW OF RESEARCH

Study background:

BRCA1 and BRCA2 are involved in repairing errors in DNA. Researchers have seen lots of DNA damage in brains cells of patients with Alzheimer’s disease. Lennart Mucke, M.D and colleagues at the Gladstone Institute of Neurological Disease and the University of California, San Francisco want to understand what DNA repair mechanisms might be involved in that damage. Although DNA damage is not known to cause Alzheimer’s disease, it is seen in Alzheimer’s patients and may be an effect of the disease.

Researchers of this study wanted to know:

Whether the DNA damage seen in the neurons of patients with Alzheimer’s could be explained by lower levels of BRCA1 protein.

Population(s) looked at in the study:

For the experiments looking at the BRCA1 levels in brains from deceased patients, researchers examined the brains of 8 patients without Alzheimer’s disease and 8 patients with Alzheimer’s disease.

Mice studies were also made:

  • mice that were genetically engineered to have some Alzheimer’s disease symptoms.
  • mice that were engineered to have less BRCA1 protein.

Each treatment group included 3 to 20 mice for the various experiments. 

Study findings: 

  1. Mice that do not have BRCA1 protein in their neurons have more DNA damage, smaller neurons and have deficiencies in learning and memory.
  2. Brains from deceased Alzheimer’s disease patients have lower BRCA1 protein levels.

Limitations:

The number of patient samples used was small: 8 samples for each group. Most of the experiments were performed in mice, however, test results from mice do not conclusively indicate what will occur in humans. Importantly, the study only reviewed normal BRCA1 genes and not BRCA1 mutations associated with increased cancer risk. 

Conclusions:

While the studies looking at mice without BRCA1 protein appear convincing regarding a potential role for BRCA1 in neuronal function, no published study has associated BRCA1 with Alzheimer’s disease.  For many years, researchers have been looking for genetic factors that increase the risk of Alzheimer’s disease—BRCA1 is not a gene that is associated with the disease. More importantly, no clinical data show that people with BRCA1 mutations have an increased risk for developing Alzheimer’s.

Some media headlines claim that BRCA1 mutations may affect Alzheimer’s disease, but this cannot be concluded from the study. Everybody is born with 2 copies of the BRCA1 gene. People with BRCA1 mutations have one "bad copy" (the one with the mutation) and one "normal copy.” This Alzheimer’s disease study looked at how normal copies of BRCA1 work in people with Alzheimer's disease, not how BRCA1 mutations affect Alzheimer’s disease.   

According to the National Institute on Aging, Alzheimer’s disease is the most common form of age-related dementia in the United States.  Given how common Alzheimer’s disease is—over 5 million Americans currently live with the disease—it is likely that some families will be affected by both BRCA1 mutations and Alzheimer’s disease, but that does not mean that the two are associated. 

For now, the reduced levels of BRCA1 in Alzheimer’s patients observed by researchers is only an observation that does not conclude anything about the effects of BRCA1 mutations on the disease.  More research needs to be done to understand the role of normal BRCA1 proteins in Alzheimer’s disease, but based on current research there is no reason to believe that BRCA1 mutations carriers are at increased risk of Alzheimer’s disease. 

References

Lambert J, Ibrahim-Verbass CA, Harold D, et al. “Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease.” Nature Genetics. 45:1452-1458 (2013). 

Suberbielle E, Djukic B, Evans M, et al. “DNA repair factor BRCA1 depletion occurs in Alzheimer brains and impairs cognitive function in mice.” Nature Communications. Published online first on November 30, 2015.  

National Institute on Aging, “Alzheimer’s Disease Fact Sheet,” (2015) 

Posted 12/22/15

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