An international group of researchers has identified 11 new genes that offer important new insights into the disease pathways involved in Alzheimer's disease. The highly collaborative effort involved scanning the DNA of over 74,000 volunteers—the largest genetic analysis yet conducted in Alzheimer's research—to discover new genetic risk factors linked to late-onset Alzheimer's disease, the most common form of the disorder.
By confirming or suggesting new processes that may influence Alzheimer's disease development—such as inflammation and synaptic function—the findings point to possible targets for the development of drugs aimed directly at prevention or delaying disease progression.
Supported in part by the National Institute on Aging (NIA) and other components of the National Institutes of Health, the International Genomic Alzheimer's Project (IGAP) reported its findings online in Nature Genetics on Oct. 27, 2013. IGAP is comprised of four consortia in the United States and Europe which have been working together since 2011 on genome-wide association studies (GWAS) involving thousands of DNA samples and shared datasets. GWAS are aimed at detecting the subtle gene variants involved in Alzheimer's and defining how the molecular mechanisms influence disease onset and progression.
"Collaboration among researchers is key to discerning the genetic factors contributing to the risk of developing Alzheimer's disease," said Richard J. Hodes, M.D., director of the NIA. "We are tremendously encouraged by the speed and scientific rigor with which IGAP and other genetic consortia are advancing our understanding."
The search for late-onset Alzheimer's risk factor genes had taken considerable time, until the development of GWAS and other techniques. Until 2009, only one gene variant, Apolipoprotein E-e4 (APOE-e4), had been identified as a known risk factor. Since then, prior to today's discovery, the list of known gene risk factors had grown to include other players—PICALM, CLU, CR1, BIN1, MS4A, CD2AP, EPHA1, ABCA7, SORL1 and TREM2.
IGAP's discovery reported today of 11 new genes strengthens evidence about the involvement of certain pathways in the disease, such as the role of the SORL1 gene in the abnormal accumulation of amyloid protein in the brain, , a hallmark of Alzheimer's disease. It also offers new gene risk factors that may influence several cell functions, to include the ability of microglial cells to respond to inflammation.
The researchers identified the new genes by analyzing previously studied and newly collected DNA data from 74,076 older volunteers with Alzheimer's and those free of the disorder from 15 countries. The new genes (HLA-DRB5/HLA0DRB1, PTK2B, SLC24A4-0RING3, DSG2, INPP5D, MEF2C, NME8, ZCWPW1, CELF1, FERMT2 and CASS4) add to a growing list of gene variants associated with onset and progression of late-onset Alzheimer's. Researchers will continue to explore the roles played by these genes, to include:
- How SORL1 and CASS4 influence amyloid, and how CASS4 and FERMT2 affect tau, another protein hallmark of Alzheimer's disease
- How inflammation is influenced by HLA-DRB5/DRB1, INPP5D, MEF2C, CR1 and TREM2
- How SORL1affects lipid transport and endocytosis (or protein sorting within cells)
- How MEF2C and PTK2B influence synaptic function in the hippocampus, a brain region important to learning and memory
- How CASS4, CELF1, NME8 and INPP5 affect brain cell function
The study also brought to light another 13 variants that merit further analysis.
"Interestingly, we found that several of these newly identified genes are implicated in a number of pathways," said Gerard Schellenberg, Ph.D., University of Pennsylvania School of Medicine, Philadelphia, who directs one of the major IGAP consortia. "Alzheimer's is a complex disorder, and more study is needed to determine the relative role each of these genetic factors may play. I look forward to our continued collaboration to find out more about these—and perhaps other—genes."
Schellenberg heads the Alzheimer's Disease Genetics Consortium (ADGC), one of the four founding partners of IGAP. The ADGC is a collaborative body established and funded by the NIA with the goal of identifying genetic variants associated with risk for Alzheimer's. Schellenberg noted that the study was made possible by the research infrastructures established and supported by the NIA over many years, including 29 Alzheimer's Disease Centers, the National Alzheimer's Coordinating Center, the NIA Genetics of Alzheimer's Disease Data Storage Site, the Late-onset Alzheimer's Disease Family Study, and the National Cell Repository for Alzheimer's Disease. These endeavors collect, store and make available to qualified researchers DNA samples, datasets containing biomedical and demographic information about participants, and genetic analysis data.
The other three founding partners of IGAP are: The Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) led by Sudha Seshadri at Boston University and supported in part by NIH (including NIH-supported databases from the AGES-Reykjavik Study and the Atherosclerosis Risk in Communities Study); the European Alzheimer's Disease Initiative (EADI) led by Philippe Amouyel of Lille University, France; and Genetic and Environmental Research in Alzheimer's Disease (GERAD) led by Julie Williams of Cardiff University, Wales.
The efforts were also supported by the Alzheimer's Association and an extensive number of international governmental, private, and public research groups.
Research goals under the U.S. National Plan to Address Alzheimer's Disease call for intensified exploration of the genetic underpinnings of the disease, with the goal of effectively treating Alzheimer's and related disorders by 2025. The 2011 National Alzheimer's Project Act (NAPA) calls for a stepped up national effort and coordination on research, care, and services for Alzheimer's and related dementias. The law mandated that the Department of Health and Human Services establish the national plan. For more on research milestones and progress under the Plan, visit http://aspe.hhs.gov/daltcp/napa/milestones/index.shtml.
The NIA leads the federal government effort conducting and supporting research on aging and the health and well-being of older people. It provides information on age-related cognitive change and neurodegenerative disease specifically at its Alzheimer's Disease Education and Referral (ADEAR) Center at http://www.nia.nih.gov/Alzheimers. For expanded information on Alzheimer's care and resources, please visit the federal government's portal website http://www.alzheimers.gov. Information on health and on aging generally can be found at http://www.nia.nih.gov. To sign up for e-mail alerts about new findings or publications, please visit either NIA website.
About the National Institutes of Health: NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical and translational medical research, and is investigating the causes, treatments and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.
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