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Alzheimer disease

Reviewed December 2008

What is Alzheimer disease?

Alzheimer disease is a degenerative disease of the brain that causes dementia, which is a gradual loss of memory, judgment, and ability to function. This disorder usually appears in people older than age 65, but less common forms of the disease appear earlier in adulthood.

Memory loss is the most common sign of Alzheimer disease. Forgetfulness may be subtle at first, but the loss of memory worsens over time until it interferes with most aspects of daily living. Even in familiar settings, a person with Alzheimer disease may get lost or become confused. Routine tasks such as preparing meals, doing laundry, and performing other household chores can be challenging. Additionally, it may become difficult to recognize people and name objects. Affected people increasingly require help with dressing, eating, and personal care.

As the disorder progresses, some people with Alzheimer disease experience personality and behavioral changes and have trouble interacting in a socially appropriate manner. Other common symptoms include agitation, restlessness, withdrawal, and loss of language skills. People with this disease usually require total care during the advanced stages of the disease. Affected individuals usually survive 8 to 10 years after the appearance of symptoms, but the course of the disease can range from 1 to 25 years. Death usually results from pneumonia, malnutrition, or general body wasting (inanition).

Alzheimer disease can be classified as early-onset or late-onset. The signs and symptoms of the early-onset form appear before age 65, while the late-onset form appears after age 65. The early-onset form is much less common than the late-onset form, accounting for less than 5 percent of all cases of Alzheimer disease.

How common is Alzheimer disease?

Alzheimer disease currently affects an estimated 2.4 million to 4.5 million Americans. Because the risk of developing Alzheimer disease increases with age and more people are living longer, the number of people with this disease is expected to increase significantly in coming decades.

What genes are related to Alzheimer disease?

Most cases of early-onset Alzheimer disease are caused by gene mutations that can be passed from parent to child. Researchers have identified mutations in three genes that cause this form of the disorder: APP, PSEN1, and PSEN2. As a result of mutations in any of these genes, large amounts of a toxic protein fragment called amyloid beta peptide are produced in the brain. This peptide can build up in the brain to form clumps called amyloid plaques, which are characteristic of Alzheimer disease. A buildup of toxic amyloid beta peptide and amyloid plaques may lead to the death of nerve cells and the progressive signs and symptoms of this disorder.

Some evidence indicates that people with Down syndrome have an increased risk of developing Alzheimer disease. Down syndrome, a condition characterized by mental retardation and other health problems, occurs when a person is born with an extra copy of chromosome 21 in each cell. As a result, people with Down syndrome have three copies of many genes in each cell, including the APP gene, instead of the usual two copies. Although the connection between Down syndrome and Alzheimer disease is unclear, the production of excess amyloid beta peptide in cells may account for the increased risk. People with Down syndrome account for less than 1 percent of all cases of Alzheimer disease.

The causes of late-onset Alzheimer disease are less clear. The late-onset form does not clearly run in families, although clusters of cases have been reported in some families. This disorder is probably related to variations in one or more genes in combination with lifestyle and environmental factors. A gene called APOE has been studied extensively as a risk factor for the disease. In particular, a variant of this gene called the e4 allele seems to increase an individual's risk for developing late-onset Alzheimer disease. Researchers are investigating many additional genes that may play a role in Alzheimer disease risk.

How do people inherit Alzheimer disease?

The early-onset form of Alzheimer disease is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the altered gene from one affected parent.

The inheritance pattern of late-onset Alzheimer disease is uncertain. People who inherit one copy of the APOE e4 allele have an increased chance of developing the disease; those who inherit two copies of the allele are at even greater risk. It is important to note that people with the APOE e4 allele inherit an increased risk of developing Alzheimer disease, not the disease itself. Not all people with Alzheimer disease have the e4 allele, and not all people who have the e4 allele will develop the disease.

Where can I find information about treatment for Alzheimer disease?

You may find information on treatment or management of Alzheimer disease or some of its symptoms in the links below, particularly the links for Gene Reviews, MedlinePlus Encyclopedia, Educational resources, and Patient support.

Where can I find additional information about Alzheimer disease?

You may find the following resources about Alzheimer disease helpful. These materials are written for the general public.

  • MedlinePlus - Health information
    • Encyclopedia: Alzheimer's Disease (http://www.nlm.nih.gov/medlineplus/ency/article/000760.htm)
    • Health Topic: Alzheimer's Caregivers (http://www.nlm.nih.gov/medlineplus/alzheimerscaregivers.html)
    • Health Topic: Alzheimer's Disease (http://www.nlm.nih.gov/medlineplus/alzheimersdisease.html)
  • Additional NIH Resources - National Institutes of Health
    • National Center for Biotechnology Information: Genes and Disease (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd.section.193)
    • National Institute of Neurological Disorders and Stroke (http://www.ninds.nih.gov/disorders/alzheimersdisease/alzheimersdisease.htm)
    • National Institute on Aging: Alzheimer's Disease Education and Referral (ADEAR) Center (http://www.alzheimers.org)
    • National Institute on Aging: Alzheimer's Disease Genetics Fact Sheet (http://www.nia.nih.gov/Alzheimers/Publications/geneticsfs.htm)
    • NIH Press Release: Scientists Isolate a Toxic Key to Alzheimer's Disease in Human Brains (June 22, 2008) (http://www.nih.gov/news/health/jun2008/nia-22.htm)
    • NIH SeniorHealth (http://nihseniorhealth.gov/alzheimersdisease/toc.html)
  • Educational resources - Information pages
    • Administration on Aging (http://www.aoa.gov/alz/)
    • American Psychiatric Association (http://healthyminds.org/mentalhealthofelderly.cfm)
    • Ask the Geneticist: Inheritance of Alzheimer disease (http://www.askthegen.org/question.php?question_id=1077)
    • Cleveland Clinic Health Information Center: Alzheimer's Disease (http://my.clevelandclinic.org/disorders/Alzheimers_Disease/hic_Alzheimers_and_Dementia_Overview.aspx)
    • Cleveland Clinic Health Information Center: Alzheimer's Disease and Down Syndrome (http://my.clevelandclinic.org/disorders/Alzheimers_Disease/hic_Alzheimers_Disease_and_Down_Syndrome.aspx)
    • Emory University School of Medicine (http://www.genetics.emory.edu/pdf/Emory_Human_Genetics_Family_History_Alzheimer_Disease.PDF)
    • Genetic Science Learning Center, University of Utah (http://learn.genetics.utah.edu/content/disorders/whataregd/alzheimers/index.html)
    • Harvard Medicine Research: Alzheimer Disease (http://hms.harvard.edu/public/disease/alzheimers/)
    • Merck Manual of Medical Information, Home Edition for Patients and Caregivers (http://www.merck.com/mmhe/sec06/ch083/ch083c.html)
    • NetWellness (http://www.netwellness.org/healthtopics/alzheimer/alzheimersgenetics.cfm)
    • New York Online Access to Health (http://www.noah-health.org/en/bns/disorders/alzheimer/)
    • Orphanet (http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=EN&Expert=1020)
    • The Wellcome Trust (http://genome.wellcome.ac.uk/doc_WTD020860.html)
  • Patient support - For patients and families
    • Alzheimer's Association (http://www.alz.org/)
    • Alzheimer's Foundation of America (http://www.alzfdn.org/)
    • Alzheimer Research Forum (http://www.alzforum.org/)
    • Family Caregiver Alliance (http://www.caregiver.org/caregiver/jsp/content_node.jsp?nodeid=567)
    • Family Village (http://www.familyvillage.wisc.edu/Lib_alzheimers.html)
    • National Organization for Rare Disorders (http://www.rarediseases.org/search/rdbdetail_abstract.html?disname=Alzheimer's+Disease)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

  • Gene Reviews - Clinical summary
    • Gene Review: Alzheimer Disease Overview (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=alzheimer)
    • Gene Review: Early-Onset Familial Alzheimer Disease (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=alzheimer-early)
  • Gene Tests - DNA tests ordered by healthcare professionals
    • DNA Test: Alzheimer Disease Risk Factor (APOE Genotype) (http://www.genetests.org/query?testid=267578)
    • DNA Test: Alzheimer Disease Type 1 (http://www.genetests.org/query?testid=53438)
    • DNA Test: Alzheimer Disease Type 3 (http://www.genetests.org/query?testid=53441)
    • DNA Test: Alzheimer Disease Type 4 (http://www.genetests.org/query?testid=53444)
  • Genetic Tools - Teaching cases (http://www.genetests.org/servlet/access?fcn=y&filename=/tools/cases/dementia-15/)
  • ClinicalTrials.gov - Linking patients to medical research (http://clinicaltrials.gov/search/condition=%22Alzheimer+disease%22)
  • PubMed - Recent literature (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=PubMed&term=(Alzheimer+Disease[MAJR])+AND+((Alzheimer+disease[TI])+OR+(Alzheimer's+disease[TI]))+AND+review[pt]+AND+english[la]+AND+human[mh]&orig_db=PubMed&filters=ON&pmfilter_EDatLimit=180+Days)
  • Online Books - Medical and science texts
    Scriver's Online Metabolic and Molecular Bases of Inherited Disease (OMMBID): Alzheimer Disease and the Frontotemporal Dementias: Diseases with Cerebral Deposition of Fibrillar Proteins (http://books.mcgraw-hill.com/getommbid.php?isbn=0071459960&template=ommbid&c=234)
  • OMIM - Genetic disorder catalog
    • OMIM topic: Alzheimer Disease Type 1 (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=104300)
    • OMIM topic: Alzheimer Disease Type 2, Late-Onset (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=104310)
    • OMIM topic: Alzheimer Disease Type 3 (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=607822)
    • OMIM topic: Alzheimer Disease Type 4 (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=606889)

What other names do people use for Alzheimer disease?

  • AD
  • Alzheimer dementia (AD)
  • Alzheimer sclerosis
  • Alzheimer's Disease
  • Alzheimer syndrome
  • Alzheimer-type dementia (ATD)
  • DAT
  • familial Alzheimer disease (FAD)
  • Presenile and senile dementia
  • Primary Senile Degenerative Dementia
  • SDAT

See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about Alzheimer disease?

  • See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.
  • Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).
  • Submit your question to Ask the Geneticist (http://www.askthegen.org/).

What glossary definitions help with understanding Alzheimer disease?

allele ; amyloid ; amyloid plaque ; autosomal ; autosomal dominant ; cell ; chromosome ; degenerative ; dementia ; familial ; gene ; inanition ; inheritance ; inheritance pattern ; mental retardation ; mutation ; nerve cell ; neurofibrillary tangles ; parkinsonism ; peptide ; plaque ; pneumonia ; protein ; risk factors ; sclerosis ; sign ; stage ; symptom ; syndrome ; tau proteins ; toxic ; wasting

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://ghr.nlm.nih.gov/glossary).

References
  • Ashford JW. APOE genotype effects on Alzheimer's disease onset and epidemiology. J Mol Neurosci. 2004;23(3):157-65. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15181244)
  • Bird TD. Genetic aspects of Alzheimer disease. Genet Med. 2008 Apr;10(4):231-9. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=18414205)
  • Bird TD. Genetic factors in Alzheimer's disease. N Engl J Med. 2005 Mar 3;352(9):862-4. No abstract available. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15745976)
  • Cummings JL. Alzheimer's disease. N Engl J Med. 2004 Jul 1;351(1):56-67. Review. No abstract available. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15229308)
  • Ertekin-Taner N. Genetics of Alzheimer's disease: a centennial review. Neurol Clin. 2007 Aug;25(3):611-67, v. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=17659183)
  • Gene Review: Early-Onset Familial Alzheimer Disease (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=alzheimer-early)
  • Harman D. Alzheimer's disease pathogenesis: role of aging. Ann N Y Acad Sci. 2006 May;1067:454-60. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=16804026)
  • Janssen JC, Beck JA, Campbell TA, Dickinson A, Fox NC, Harvey RJ, Houlden H, Rossor MN, Collinge J. Early onset familial Alzheimer's disease: Mutation frequency in 31 families. Neurology. 2003 Jan 28;60(2):235-9. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=12552037)
  • Kamboh MI. Molecular genetics of late-onset Alzheimer's disease. Ann Hum Genet. 2004 Jul;68(Pt 4):381-404. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15225164)
  • Li Y, Grupe A. Genetics of late-onset Alzheimer's disease: progress and prospect. Pharmacogenomics. 2007 Dec;8(12):1747-55. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=18086004)
  • Lott IT, Head E. Alzheimer disease and Down syndrome: factors in pathogenesis. Neurobiol Aging. 2005 Mar;26(3):383-9. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15639317)
  • Lott IT, Head E. Down syndrome and Alzheimer's disease: a link between development and aging. Ment Retard Dev Disabil Res Rev. 2001;7(3):172-8. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=11553933)
  • Mattson MP. Pathways towards and away from Alzheimer's disease. Nature. 2004 Aug 5;430(7000):631-9. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=15295589)
  • Nussbaum RL, Ellis CE. Alzheimer's disease and Parkinson's disease. N Engl J Med. 2003 Apr 3;348(14):1356-64. Review. No abstract available. Erratum in: N Engl J Med. 2003 Jun 19;348(25):2588. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=12672864)
  • Papassotiropoulos A, Fountoulakis M, Dunckley T, Stephan DA, Reiman EM. Genetics, transcriptomics, and proteomics of Alzheimer's disease. J Clin Psychiatry. 2006 Apr;67(4):652-70. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=16669732)
  • Rocchi A, Pellegrini S, Siciliano G, Murri L. Causative and susceptibility genes for Alzheimer's disease: a review. Brain Res Bull. 2003 Jun 30;61(1):1-24. Review. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=retrieve&db=pubmed&dopt=Abstract&list_uids=12788204)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: December 2008
Published: January 12, 2009