alzheimers causes

Importance of vascular factors in Alzheimer's disease

Analysis of 5715 cases from the National Alzheimer's Coordinating Center (NACC) database has found that nearly 80% of more than 4600 Alzheimer's disease patients showed some degree of vascular pathology, compared with 67% of the controls, and 66% in the Parkinson's group. The link was especially strong for younger patients with Alzheimer’s.

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Impaired recovery from inflammation linked to Alzheimer's

Analyses of cerebrospinal fluid from 15 patients with Alzheimer's disease, 20 patients with mild cognitive impairment, and 21 control subjects, plus brain tissue from some of them, has found that those with Alzheimer’s had lower levels of a particular molecule involved in resolving inflammation. These ‘specialized pro-resolving mediators’ regulate the tidying up of the damage done by inflammation and the release of growth factors that stimulate tissue repair.

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How inflammation and hypoxia damage the brain

A new study shows that a combination of inflammation and hypoxia activates microglia in a way that persistently weakens the connection between neurons, contributing to brain damage in conditions such as stroke and Alzheimer's disease.

http://www.eurekalert.org/pub_releases/2014-03/uobc-scb031214.php

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Alzheimer's: Causes

Older news items (pre-2010) brought over from the old website

Role of fatty acids in Alzheimer's disease

Fatty acids are rapidly taken up by the brain and incorporated into phospholipids, a class of fats that form the membrane or barrier that shields the content of cells from the external environment. Now genetically engineered mice have revealed that there is a striking increase in arachidonic acid and related metabolites in the hippocampus. Removal or reduction of the enzyme that releases this acid prevented memory deficits in the Alzheimer mice. It’s thought that the acid causes too much excitation.

Sanchez-Mejia, R.O. et al. 2008. Phospholipase A2 reduction ameliorates cognitive deficits in a mouse model of Alzheimer's disease. Nature Neuroscience, 11, 1311-1318.

http://www.eurekalert.org/pub_releases/2008-10/gi-gsi101408.php

Support for view of Alzheimer's as form of diabetes

Research in the last few years has raised the possibility that Alzheimer’s memory loss could be due to a third form of diabetes. A new study clarifies the connection between insulin and Alzheimer’s. It seems that the toxic protein ADDL, found in the brains of individuals with Alzheimer’s, removes insulin receptors from nerve cells, rendering those neurons insulin resistant. The findings suggest that some existing drugs now used to treat diabetic patients may be useful for Alzheimer’s treatment.

Zhao,W-Q. et al. 2007. Amyloid beta oligomers induce impairment of neuronal insulin receptors. FASEB Journal, published online ahead of print August 24.

http://www.eurekalert.org/pub_releases/2007-09/nu-dst092607.php

Link between size of hippocampus and progression to Alzheimer's

A study of 20 older adults with mild cognitive impairment has found that the hippocampus was smaller in those who developed into Alzheimer's during the 3 year period.

Apostolova, L.G. et al. 2006. Conversion of Mild Cognitive Impairment to Alzheimer Disease Predicted by Hippocampal Atrophy Maps. Archives of Neurology, 63, 693-699.

http://www.eurekalert.org/pub_releases/2006-05/uoc--rml050406.php

Post-mortem brain studies reveal features of mild cognitive impairment

Autopsies have revealed that the brains of patients with mild cognitive impairment display pathologic features that appear to place them at an intermediate stage between normal aging and Alzheimer's disease. For instance, the patients had begun developing neurofibrillary tangles, but the number of plaques was similar to that in healthy patients. All patients with mild cognitive impairment had abnormalities in their temporal lobes, which likely caused their cognitive difficulties, and many also had abnormalities in other areas that did not relate to the features of Alzheimer's disease. In a second study, of 34 patients with mild cognitive impairment who had progressed to clinical dementia before their deaths, 24 were diagnosed (post-mortem) with Alzheimer’s, and 10 with other types of dementia. As in the other study, all patients had abnormalities in their temporal lobes.

Petersen, R.C. et al. 2006. Neuropathologic Features of Amnestic Mild Cognitive Impairment. Archives of Neurology, 63, 665-672.

Jicha, G.A. et al. 2006. Neuropathologic Outcome of Mild Cognitive Impairment Following Progression to Clinical Dementia. Archives of Neurology, 63, 674-681.

http://www.eurekalert.org/pub_releases/2006-05/jaaj-pbs050406.php

Neurons can produce apolipoprotein E

Apolipoprotein E has been known to be synthesized in the brain in support cells such as astrocytes, microglia, and ependymal layer cells. Controversial for the last decade has been the question of whether or not neurons can produce apoE. Using a unique mouse model, researchers have now demonstrated that neurons can produce apoE, but only in response to injury to the brain.

Xu, Q. et al. 2006. Profile and Regulation of Apolipoprotein E (ApoE) Expression in the CNS in Mice with Targeting of Green Fluorescent Protein Gene to the ApoE Locus. Journal of Neuroscience, 26, 4985-4994.

http://www.eurekalert.org/pub_releases/2006-05/gi-gsp051006.php

Protein identified as cause of memory loss

Researchers have identified a substance in the brain that is proven to cause memory loss, giving drug developers a target for creating drugs to treat memory loss in people with dementia. The substance is a form of the amyloid-beta protein that is distinct from plaques and has been given the name Ab*56. Ab*56 impairs memory independently of plaques or neuronal loss, and may contribute to cognitive deficits associated with Alzheimer's disease.

Lesné, S. et al. 2006. A specific amyloid-beta protein assembly in the brain impairs memory. Nature, 440, 352-357.

http://www.eurekalert.org/pub_releases/2006-03/uom-uom_1031306.php

Reduced insulin in the brain triggers Alzheimer's degeneration

By depleting insulin and its related proteins in the brain, researchers have replicated the progression of Alzheimer's disease – including plaque deposits, neurofibrillary tangles, impaired cognitive functioning, cell loss and overall brain deterioration – in an experimental animal model. Brain deterioration was not related to the pancreas, raising the possibility that Alzheimer's is a neuroendocrine disorder, or a Type 3 diabetes.

Lester-Coll, N. et al. 2006. Intracerebral streptozotocin model of type 3 diabetes: relevance to sporadic Alzheimer’s disease. Journal of Alzheimer’s Disease, 9(1)

http://www.eurekalert.org/pub_releases/2006-03/l-rii031606.php

Pin1 enzyme key in preventing onset of Alzheimer's disease

An enzyme called Pin1, previously shown to prevent the formation of the tangles characteristic of Alzheimer's brains, has now been shown to also play a pivotal role in guarding against the development of the plaques that are also characteristic of Alzheimer's. These findings establish a direct link between amyloid plaques and tau tangles, and provide further evidence that Pin1 (prolyl isomerase) is essential to protect individuals from age-related neurodegeneration.

Pastorino, L. et al. 2006. The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production Nature, 440, 528-534.

http://www.eurekalert.org/pub_releases/2006-03/hms-nrs032006.php

Link between APOE and memory neurotransmitter

A new link in the complex chain of Alzheimer’s development has been found. It’s been found that receptors that bind apolipoprotein E (APOE) and those that bind glutamate are in fact connected, separated only by a small protein. It may be that inefficient or high levels of APOE are clogging these binding sites, preventing glutamate from activating the processes necessary to form memories. It may also be that the APOE4 variant — associated with Alzheimer's — is less efficient at removing lipid debris in the brain than is APOE2 or APOE3.

Hoe, H-S. et al. 2006. Apolipoprotein E Receptor 2 Interactions with the N-Methyl-D-aspartate Receptor. Journal of Biological Chemistry, 281, 3425-3431.

http://www.eurekalert.org/pub_releases/2006-02/gumc-nrr020906.php

Two pathways lead to Alzheimer's disease

Mild cognitive impairment (MCI), a transitional stage between normal cognition and Alzheimer's disease, has been categorized into two sub-types on the basis of differing symptoms. Those with the amnesic subtype (MCI-A) have memory impairments only, while those with the multiple cognitive domain subtype (MCI-MCD) have other types of mild impairments, such as in judgment or language, and mild or no memory loss. Both sub-types progress to Alzheimer's disease at the same rate. A new imaging technique has now revealed that these types do in fact have different pathologies. The hippocampus of patients with MCI-A was not significantly different from that of Alzheimer's patients (who show substantial shrinkage), but the hippocampus of those with MCI-MCD was not significantly different from that of the healthy controls.

Becker, J.T., Davis, S.W., Hayashi, K.M., Meltzer, C.C., Toga, A.W., Lopez, O.L., Thompson, P.M., for the Imaging Methods and Analysis in Geriatrics Research Group. 2006. Three-dimensional Patterns of Hippocampal Atrophy in Mild Cognitive Impairment. Archives of Neurology, 63, 97-101.

http://www.eurekalert.org/pub_releases/2006-01/uopm-tpf010606.php

Key genetic risk for Alzheimer's linked to myelin breakdown

Myelin, the fatty insulation coating the brain's internal wiring, builds up in childhood, and breaks down as we age. Myelin is critical for speedy communication between neurons. A new study supports a growing body of evidence that myelin breakdown is a key contributor to the onset of Alzheimer disease later in life. Moreover, it has also revealed that the severity and rate of myelin breakdown in healthy older individuals is associated with ApoE status. Thus both age, the most important risk factor for Alzheimer disease, and ApoE status, the second-most important risk factor, seem to act through the process of myelin breakdown.

Bartzokis, G., Lu, P.H., Geschwind, D.H., Edwards, N., Mintz, J. & Cummings, J.L. 2006. Apolipoprotein E Genotype and Age-Related Myelin Breakdown in Healthy Individuals: Implications for Cognitive Decline and Dementia. Archives of General Psychiatry, 63, 63-72.

http://www.eurekalert.org/pub_releases/2006-01/uoc--isl122805.php

Study links Alzheimer's and Down’s syndrome

New research suggests the cognitive problems observed in Alzheimer’s are related to defects in the machinery controlling neuronal connections — PAK enzyme signaling pathways. PAK (p21-activated kinase) enzymes form a family that includes two members (PAK1 and PAK3) that play critical roles in learning and memory. Humans with genetic loss of PAK3 have severe mental retardation. The study reveals that both PAK1 and PAK3 are abnormally distributed and reduced in Alzheimer patients, and that beta-amyloid was directly involved in PAK signaling deficits. The finding suggests therapies designed to address the PAK defect could treat cognitive problems in both patient populations.

Zhao, L. et al. 2006. Role of p21-activated kinase pathway defects in the cognitive deficits of Alzheimer disease. Nature Neuroscience, 9, 234–242.

http://www.eurekalert.org/pub_releases/2006-01/uoc--sid012506.php

New technique finds higher levels of creatine in Alzheimer’s brains

Creatine is involved in the maintaining the energy balance in the brain, but creatine, being small and very soluble, is difficult to detect. A new study has now succeeded in detecting creatine in situ, in brain tissue, and has found relatively large deposits in the hippocampus of Alzheimer’s brains. The finding suggests an overlooked aspect of energy disturbance in Alzheimer's disease, but further research is needed to understand it.
Gallant, M. et al. 2006. Focally Elevated Creatine Detected in Amyloid Precursor Protein (APP) Transgenic Mice and Alzheimer Disease Brain Tissue. Journal of Biological Chemistry, 281, 5-8.
http://www.eurekalert.org/pub_releases/2005-12/uow-iar122105.php

More light on apoE4 and Alzheimer’s

A mutant form of a protein that transports cholesterol, apolipoprotein E (apoE) has long been recognized as a causative factor for Alzheimer's disease, but exactly how has been unclear. 299 amino acids are associated with apoE4, but new research has now found which of these amino acids are toxic. These toxic fragments all reside in the mitochondria (the “energy powerhouse” of the cell). The finding suggests a new therapeutic approach, involving blocking interaction of apoE4 fragments with the mitochondria.

Ye, S. et al. 2005. Apolipoprotein (apo) E4 enhances amyloid peptide production in cultured neuronal cells: ApoE structure as a potential therapeutic target. Proceedings of the National Academy of Science, 102 (51), 18700-18705.

http://www.eurekalert.org/pub_releases/2005-12/gi-gsl121405.php

p25 only good in small doses

Elevated levels of a key brain regulatory enzyme called Cdk5 and an associated regulatory protein called p25 have been found in the brains of Alzheimer’s patients. A new mouse study has found that switching on p25 in the hippocampus for only two weeks actually enhanced learning and memory compared to normal mice; however mice in which p25 had been switched on for six weeks showed impaired learning and memory. These mice also showed significant brain atrophy and loss of hippocampal neurons. The two-week pulse of p25 did not cause neurodegeneration and had long-lasting effects on enhancing memory. The researchers suggest that p25 might be produced to compensate for the loss of Cdk5 activity during aging, however chronically high levels lead to neuronal cell death. The findings are consistent with several recent studies suggesting that in the development of Alzheimer’s, compensatory mechanisms that initially enhance neuroplasticity eventually become maladaptive when chronically activated.

Fischer, A., Sananbenesi, F., Pang, P.T., Lu, B. & Tsai, L-H. 2005. Opposing roles of transient and prolonged expression of p25 in synaptic plasticity and hippocampus-dependent memory. Neuron, 48, 825–838.

http://www.eurekalert.org/pub_releases/2005-12/cp-aje120505.php

“Default” brain activity implicated in Alzheimer's disease

Here’s an unexpected finding: imaging of the brains of 764 adults of various ages has revealed that the regions that are active when people are in “default mode” — not concentrating on anything in particular, just musing to yourself — are the same regions that develop plaques in Alzheimer’s. They also found that, when asked to concentrate on a specific task, individuals with Alzheimer’s showed increased activity in these posterior cortical regions, rather than the decreased activity seen in young, healthy adults. The researchers speculate that dementia may in fact be a consequence of normal cognitive function — a possibility that hasn’t heretofore been considered. The findings raise the hope of developing methods to detect precursors of the disease long before it develops.

Buckner, R.L. et al. 2005. Molecular, Structural, and Functional Characterization of Alzheimer's Disease: Evidence for a Relationship between Default Activity, Amyloid, and Memory. Journal of Neuroscience, 25, 7709-7717.

http://www.eurekalert.org/pub_releases/2005-08/hhmi-bai082405.php

How Alzheimer's impacts important brain cell function

Researchers have found that synaptic proteins, proteins involved in brain cell communications, decrease in the brains of Alzheimer's patients compared to healthy brains from people in the same age range. The decrease in the frontal cortex was more severe than in other portions of the brain. They also found synaptic protein levels were even lower in the brains of patients in the early stages of Alzheimer's disease, suggesting that the loss of these proteins happens very early in the disease process. The reduction of synaptic proteins may be caused by mitochondrial dysfunction, a well-documented occurrence in Alzheimer's.

Reddy, P.H., Mani, G., Park, B.S., Jacques, J., Murdoch, G., Whetsell, W.Jr., Kaye, J. & Manczak, M. 2005. Differential loss of synaptic proteins in Alzheimer’s disease: Implications for synaptic dysfunction Journal of Alzheimer's Disease, 7(2),103-117.

http://www.eurekalert.org/pub_releases/2005-04/ohs-ord040605.php

Research clarifies how Alzheimer's medicines work

New research clarifies how cholinesterase inhibitors alleviate mild-to-moderate Alzheimer's. When scientists chemically blocked receptors for an important neurotransmitter called acetylcholine, even healthy young people found it significantly harder to learn and remember – especially in the face of interference. Cholinesterase inhibitors slow the breakdown of acetylcholine. The finding also helps explain why Parkinson's disease, dementia due to multiple strokes, multiple sclerosis and schizophrenia, are all also associated with memory problems — all these conditions, like Alzheimer’s, are associated with lower levels of acetylcholine in the brain.

Atri, A., Norman, K.A., Nicolas, M.M., Cramer, S.C., Hasselmo, M.E., Sherman, S., Kirchhoff, B.A., Greicius, M.D., Breiter, H.C. & Stern, C.E. 2004. Central Cholinergic Receptors Impairs New Learning and Increases Proactive Interference in a Word Paired-Associate Memory Task. Behavioral Neuroscience, 118 (1).

http://www.eurekalert.org/pub_releases/2004-02/apa-rch020904.php

Why diet, hormones, exercise might delay Alzheimer’s

A theory that changes in fat metabolism in the membranes of nerve cells play a role in Alzheimer's has been supported in a recent study. The study found significantly higher levels of ceramide and cholesterol in the middle frontal gyrus of Alzheimer's patients. The researchers suggest that alterations in fats (especially cholesterol and ceramide) may contribute to a "neurodegenerative cascade" that destroys neurons in Alzheimer's, and that the accumulation of ceramide and cholesterol is triggered by the oxidative stress brought on by the presence of the toxic beta amyloid peptide. The study also suggests a reason for why antioxidants such as vitamin E might delay the onset of Alzheimer's: treatment with Vitamin E reduced the levels of ceramide and cholesterol, resulting in a significant decrease in the number of neurons killed by the beta amyloid and oxidative stress.

Cutler, R.G., Kelly, J., Storie, K., Pedersen, W.A., Tammara, A., Hatanpaa, K., Troncoso, J.C. & Mattson, M.P. 2004. Involvement of oxidative stress-induced abnormalities in ceramide and cholesterol metabolism in brain aging and Alzheimer's disease. PNAS, 101, 2070-5.

http://www.eurekalert.org/pub_releases/2004-02/aaft-nsm021004.php

Late-life Alzheimer's begins in midlife

A new model of human brain aging identifies midlife breakdown of myelin, a fatty insulation with very high cholesterol content that wraps tightly around axons (part of the neurons) and enables messages to pass along the “wiring” of the brain speedily, as a possible key to the onset of Alzheimer's disease later in life. Imaging studies and examination of brain tissue shows that the brain's wiring develops until middle age and then begins to decline as the breakdown of myelin triggers a destructive domino affect. It is suggested that genetic factors coupled with the brain's own developmental process of increasing cholesterol and iron levels in middle age help degrade the myelin. The complex connections that take the longest to develop and allow humans to think at their highest level are among the first to deteriorate as the brain's myelin breaks down in reverse order of development. The model suggests that the best time to address the inevitability of myelin breakdown is when it begins, in middle age. Possible preventive therapies include cholesterol- and iron-lowering medications, anti-inflammatory medications, diet and exercise programs and possibly hormone replacement therapy designed to prevent menopause rather than simply ease the symptoms. Education and cognitively stimulating activities may also stimulate the production of myelin.

Bartzokis, G. 2003. Age-related myelin breakdown: a developmental model of cognitive decline and Alzheimer's disease. Neurobiology of Aging, 25(1), 5-18.

http://www.eurekalert.org/pub_releases/2003-12/uoc--mbc122303.php

A nicotine by-product implicated in Alzheimer’s

A previously unrecognized chemical process has been discovered, by which a chemical called nornicotine, naturally present in tobacco and produced as a metabolite of nicotine, permanently and irreversibly modifies proteins in the body. These modified proteins interact with other chemicals in the body to form a variety of compounds known as advanced glycation endproducts. Advanced glycation endproducts have previously been implicated in numerous diseases including diabetes, cancer, atherosclerosis, and Alzheimer’s disease.

Dickerson, T.J. & Janda, K.D. 2002. A previously undescribed chemical link between smoking and metabolic disease. Proc. Natl. Acad. Sci. USA, 99 (23), 15084-15088.

http://www.eurekalert.org/pub_releases/2002-10/sri-aka102402.php

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Are sleep problems a key factor in Alzheimer’s?

October, 2012

A mouse study shows that sleep deprivation and aggregation of amyloid beta go hand in hand, and may be key players on the road to Alzheimer’s.

I reported a few months ago on some evidence of a link between disturbed sleep and the development of Alzheimer’s. Now a mouse study adds to this evidence.

The mouse study follows on from an earlier study showing that brain levels of amyloid beta naturally rise when healthy young mice are awake and drop after they go to sleep, and that sleep deprivation disrupted this cycle and accelerated the development of amyloid plaques. This natural rhythm was confirmed in humans.

In the new study, it was found that this circadian rhythm showed the first signs of disruption as soon as Alzheimer’s plaques began forming in the mice’s brains. When the genetically engineered mice were given a vaccine against amyloid beta, the mice didn’t develop plaques in old age, the natural fluctuations in amyloid beta levels continued, and sleep patterns remained normal.

Research with humans in now underway to see whether patients with early markers of Alzheimer’s show sleep problems, and what the nature of these problems is.

Just to make it clear: the point is not so much that Alzheimer’s patients are more likely to have sleep problems, but that the sleep problems may in fact be part of the cause of Alzheimer’s disease development. The big question, of course, is whether you can prevent its development by attacking the dysfunction in circadian rhythm. (See more on this debate at Biomed)

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Genes, brain size, brain atrophy, and Alzheimer’s risk

May, 2012

A round-up of genetic news.

  • Several genes are linked to smaller brain size and faster brain atrophy in middle- & old age.
  • The main Alzheimer's gene is implicated in leaky blood vessels, and shown to interact with brain size, white matter lesions, and dementia risk.
  • Some evidence suggests early-onset Alzheimer's is not so dissimilar to late-onset Alzheimer's.

Genetic analysis of 9,232 older adults (average age 67; range 56-84) has implicated four genes in how fast your hippocampus shrinks with age (rs7294919 at 12q24, rs17178006 at 12q14, rs6741949 at 2q24, rs7852872 at 9p33). The first of these (implicated in cell death) showed a particularly strong link to a reduced hippocampus volume — with average consequence being a hippocampus of the same size as that of a person 4-5 years older.

Faster atrophy in this crucial brain region would increase people’s risk of Alzheimer’s and cognitive decline, by reducing their cognitive reserve. Reduced hippocampal volume is also associated with schizophrenia, major depression, and some forms of epilepsy.

In addition to cell death, the genes linked to this faster atrophy are involved in oxidative stress, ubiquitination, diabetes, embryonic development and neuronal migration.

A younger cohort, of 7,794 normal and cognitively compromised people with an average age of 40, showed that these suspect gene variants were also linked to smaller hippocampus volume in this age group. A third cohort, comprised of 1,563 primarily older people, showed a significant association between the ASTN2 variant (linked to neuronal migration) and faster memory loss.

In another analysis, researchers looked at intracranial volume and brain volume in 8,175 elderly. While they found no genetic associations for brain volume (although there was one suggestive association), they did discover that intracranial volume (the space occupied by the fully developed brain within the skull — this remains unchanged with age, reflecting brain size at full maturity) was significantly associated with two gene variants (at loci rs4273712, on chromosome 6q22, and rs9915547, on 17q21). These associations were replicated in a different sample of 1,752 older adults. One of these genes is already known to play a unique evolutionary role in human development.

A meta-analysis of seven genome-wide association studies, involving 10,768 infants (average age 14.5 months), found two loci robustly associated with head circumference in infancy (rs7980687 on chromosome 12q24 and rs1042725 on chromosome 12q15). These loci have previously been associated with adult height, but these effects on infant head circumference were largely independent of height. A third variant (rs11655470 on chromosome 17q21 — note that this is the same chromosome implicated in the study of older adults) showed suggestive evidence of association with head circumference; this chromosome has also been implicated in Parkinson's disease and other neurodegenerative diseases.

Previous research has found an association between head size in infancy and later development of Alzheimer’s. It has been thought that this may have to do with cognitive reserve.

Interestingly, the analyses also revealed that a variant in a gene called HMGA2 (rs10784502 on 12q14.3) affected intelligence as well as brain size.

Why ‘Alzheimer’s gene’ increases Alzheimer’s risk

Investigation into the so-called ‘Alzheimer’s gene’ ApoE4 (those who carry two copies of this variant have roughly eight to 10 times the risk of getting Alzheimer’s disease) has found that ApoE4 causes an increase in cyclophilin A, which in turn causes a breakdown of the cells lining the blood vessels. Blood vessels become leaky, making it more likely that toxic substances will leak into the brain.

The study found that mice carrying the ApoE4 gene had five times as much cyclophilin A as normal, in cells crucial to maintaining the integrity of the blood-brain barrier. Blocking the action of cyclophilin A brought blood flow back to normal and reduced the leakage of toxic substances by 80%.

The finding is in keeping with the idea that vascular problems are at the heart of Alzheimer’s disease — although it should not be assumed from that, that other problems (such as amyloid-beta plaques and tau tangles) are not also important. However, one thing that does seem clear now is that there is not one single pathway to Alzheimer’s. This research suggests a possible treatment approach for those carrying this risky gene variant.

Note also that this gene variant is not only associated with Alzheimer’s risk, but also Down’s syndrome dementia, poor outcome following TBI, and age-related cognitive decline.

On which note, I’d like to point out recent findings from the long-running Nurses' Health Study, involving 16,514 older women (70-81), that suggest that effects of postmenopausal hormone therapy for cognition may depend on apolipoprotein E (APOE) status, with the fastest rate of decline being observed among HT users who carried the APOe4 variant (in general HT was associated with poorer cognitive performance).

It’s also interesting to note another recent finding: that intracranial volume modifies the effect of apoE4 and white matter lesions on dementia risk. The study, involving 104 demented and 135 nondemented 85-year-olds, found that smaller intracranial volume increased the risk of dementia, Alzheimer's disease, and vascular dementia in participants with white matter lesions. However, white matter lesions were not associated with increased dementia risk in those with the largest intracranial volume. But intracranial volume did not modify dementia risk in those with the apoE4 gene.

More genes involved in Alzheimer’s

More genome-wide association studies of Alzheimer's disease have now identified variants in BIN1, CLU, CR1 and PICALM genes that increase Alzheimer’s risk, although it is not yet known how these gene variants affect risk (the present study ruled out effects on the two biomarkers, amyloid-beta 42 and phosphorylated tau).

Same genes linked to early- and late-onset Alzheimer's

Traditionally, we’ve made a distinction between early-onset Alzheimer's disease, which is thought to be inherited, and the more common late-onset Alzheimer’s. New findings, however, suggest we should re-think that distinction. While the genetic case for early-onset might seem to be stronger, sporadic (non-familial) cases do occur, and familial cases occur with late-onset.

New DNA sequencing techniques applied to the APP (amyloid precursor protein) gene, and the PSEN1 and PSEN2 (presenilin) genes (the three genes linked to early-onset Alzheimer's) has found that rare variants in these genes are more common in families where four or more members were affected with late-onset Alzheimer’s, compared to normal individuals. Additionally, mutations in the MAPT (microtubule associated protein tau) gene and GRN (progranulin) gene (both linked to frontotemporal dementia) were also found in some Alzheimer's patients, suggesting they had been incorrectly diagnosed as having Alzheimer's disease when they instead had frontotemporal dementia.

Of the 439 patients in which at least four individuals per family had been diagnosed with Alzheimer's disease, rare variants in the 3 Alzheimer's-related genes were found in 60 (13.7%) of them. While not all of these variants are known to be pathogenic, the frequency of mutations in these genes is significantly higher than it is in the general population.

The researchers estimate that about 5% of those with late-onset Alzheimer's disease have changes in these genes. They suggest that, at least in some cases, the same causes may underlie both early- and late-onset disease. The difference being that those that develop it later have more protective factors.

Another gene identified in early-onset Alzheimer's

A study of the genes from 130 families suffering from early-onset Alzheimer's disease has found that 116 had mutations on genes already known to be involved (APP, PSEN1, PSEN2 — see below for some older reports on these genes), while five of the other 14 families all showed mutations on a new gene: SORL1.

I say ‘new gene’ because it hasn’t been implicated in early-onset Alzheimer’s before. However, it has been implicated in the more common late-onset Alzheimer’s, and last year a study reported that the gene was associated with differences in hippocampal volume in young, healthy adults.

The finding, then, provides more support for the idea that some cases of early-onset and late-onset Alzheimer’s have the same causes.

The SORL1 gene codes for a protein involved in the production of the beta-amyloid peptide, and the mutations seen in this study appear to cause an under-expression of SORL1, resulting in an increase in the production of the beta-amyloid peptide. Such mutations were not found in the 1500 ethnicity-matched controls.

 

Older news reports on these other early-onset genes (brought over from the old website):

New genetic cause of Alzheimer's disease

Amyloid protein originates when it is cut by enzymes from a larger precursor protein. In very rare cases, mutations appear in the amyloid precursor protein (APP), causing it to change shape and be cut differently. The amyloid protein that is formed now has different characteristics, causing it to begin to stick together and precipitate as amyloid plaques. A genetic study of Alzheimer's patients younger than 70 has found genetic variations in the promoter that increases the gene expression and thus the formation of the amyloid precursor protein. The higher the expression (up to 150% as in Down syndrome), the younger the patient (starting between 50 and 60 years of age). Thus, the amount of amyloid precursor protein is a genetic risk factor for Alzheimer's disease.

Theuns, J. et al. 2006. Promoter Mutations That Increase Amyloid Precursor-Protein Expression Are Associated with Alzheimer Disease. American Journal of Human Genetics, 78, 936-946.

http://www.eurekalert.org/pub_releases/2006-04/vfii-rda041906.php

Evidence that Alzheimer's protein switches on genes

Amyloid b-protein precursor (APP) is snipped apart by enzymes to produce three protein fragments. Two fragments remain outside the cell and one stays inside. When APP is produced in excessive quantities, one of the cleaved segments that remains outside the cell, called the amyloid b-peptides, clumps together to form amyloid plaques that kill brain cells and may lead to the development of Alzheimer’s disease. New research indicates that the short "tail" segment of APP that is trapped inside the cell might also contribute to Alzheimer’s disease, through a process called transcriptional activation - switching on genes within the cell. Researchers speculate that creation of amyloid plaque is a byproduct of a misregulation in normal APP processing.

[2866] Cao, X., & Südhof T. C.
(2001).  A Transcriptively Active Complex of APP with Fe65 and Histone Acetyltransferase Tip60.
Science. 293(5527), 115 - 120.

http://www.eurekalert.org/pub_releases/2001-07/aaft-eta070201.php

Inactivation of Alzheimer's genes in mice causes dementia and brain degeneration

Mutations in two related genes known as presenilins are the major cause of early onset, inherited forms of Alzheimer's disease, but how these mutations cause the disease has not been clear. Since presenilins are involved in the production of amyloid peptides (the major components of amyloid plaques), it was thought that such mutations might cause Alzheimer’s by increasing brain levels of amyloid peptides. Accordingly, much effort has gone into identifying compounds that could block presenilin function. Now, however, genetic engineering in mice has revealed that deletion of these genes causes memory loss and gradual death of nerve cells in the mouse brain, demonstrating that the protein products of these genes are essential for normal learning, memory and nerve cell survival.

Saura, C.A., Choi, S-Y., Beglopoulos, V., Malkani, S., Zhang, D., Shankaranarayana Rao, B.S., Chattarji, S., Kelleher, R.J.III, Kandel, E.R., Duff, K., Kirkwood, A. & Shen, J. 2004. Loss of Presenilin Function Causes Impairments of Memory and Synaptic Plasticity Followed by Age-Dependent Neurodegeneration. Neuron, 42 (1), 23-36.

http://www.eurekalert.org/pub_releases/2004-04/cp-ioa032904.php

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