Molecular genetics of Alzheimer's disease

Oxidative stress and amyloid-beta pathology in normal individuals with a maternal history of Alzheimer's

BACKGROUND

Epidemiology and imaging studies showed that cognitively normal (NL) individuals with a maternal history (MH) of late-onset Alzheimer's disease (LOAD) might be at increased risk for Alzheimer's disease (AD) compared with NL with a paternal history (PH) and NL with a negative family history of LOAD (NH). With a panel of cerebrospinal fluid (CSF) markers, this study examined whether NL MH showed evidence for AD pathology compared with PH and NH.

METHODS

Fifty-nine 40-80-year-old NL subjects were examined, including 23 MH and 14 PH whose parents had a clinician-certified diagnosis of LOAD and 22 NH. All subjects completed clinical neuropsychological examinations and a lumbar puncture to measure CSF levels of amyloid-beta (Aβ(40), Aβ(42), Aβ(42/40)), total and hyperphosphorylated tau (T-Tau and P-Tau(231); markers of axonal degeneration and neurofibrillary tangles, respectively), and F₂-isoprostanes (IsoP) (a marker of oxidative stress).

RESULTS

Groups were comparable for demographic and neuropsychological measures. The MH subjects showed higher IsoP and reduced Aβ(42/40) CSF levels compared with NH and with PH (p values ≤ .05), whereas no differences were found between NH and PH. No group differences were found for P-Tau(231) and T-Tau. The IsoP and Aβ(42/40) levels were correlated only within the MH group (R² = .32, p = .005) and discriminated MH from the other subjects with 70% accuracy (relative risk = 3.7%, 95% confidence interval = 1.6-9.7, p < .001). Results remained significant controlling for age, gender, education, and apolipoprotein E genotype.

CONCLUSIONS

Adult children of LOAD-affected mothers express a pathobiological phenotype characterized by Aβ-associated oxidative stress consistent with AD, which might reflect increased risk for developing the disease.

Oleic acid ameliorates amyloidosis in cellular and mouse models of Alzheimer's disease

Several lines of evidence support protective as well as deleterious effects of oleic acid (OA) on Alzheimer's disease (AD) and other neurological disorders; however, the bases of these effects are unclear. Our investigation demonstrates that amyloid precursor protein (APP) 695 transfected Cos-7 cells supplemented with OA have reduced secreted amyloid-beta (Aβ) levels. An early-onset AD transgenic mouse model expressing the double-mutant form of human APP, Swedish (K670N/M671L) and Indiana (V717F), corroborated our in vitro findings when they were fed a high-protein, low-fat (18% reduction), cholesterol-free diet enriched with OA. These mice exhibited an increase in Aβ40/Aβ42 ratio, reduced levels of beta-site APP cleaving enzyme (BACE) and reduced presenilin levels along with reduced amyloid plaques in the brain. The decrease in BACE levels was accompanied by increased levels of a non-amyloidogenic soluble form of APP (sAPPα). Furthermore, the low-fat/+OA diet resulted in an augmentation of insulin-degrading enzyme and insulin-like growth factor-II. These results suggest that OA supplementation and cholesterol intake restriction in a mouse model of AD reduce AD-type neuropathology.

Aberrant amyloid precursor protein (APP) processing in hereditary forms of Alzheimer disease caused by APP familial Alzheimer disease mutations can be rescued by mutations in the APP GxxxG motif

The identification of hereditary familial Alzheimer disease (FAD) mutations in the amyloid precursor protein (APP) and presenilin-1 (PS1) corroborated the causative role of amyloid-beta peptides with 42 amino acid residues (Abeta42) in the pathogenesis of AD. Although most FAD mutations are known to increase Abeta42 levels, mutations within the APP GxxxG motif are known to lower Abeta42 levels by attenuating transmembrane sequence dimerization. Here, we show that aberrant Abeta42 levels of FAD mutations can be rescued by GxxxG mutations. The combination of the APP-GxxxG mutation G33A with APP-FAD mutations yielded a constant 60% decrease of Abeta42 levels and a concomitant 3-fold increase of Abeta38 levels compared with the Gly(33) wild-type as determined by ELISA. In the presence of PS1-FAD mutations, the effects of G33A were attenuated, apparently attributable to a different mechanism of PS1-FAD mutants compared with APP-FAD mutants. Our results contribute to a general understanding of the mechanism how APP is processed by the gamma-secretase module and strongly emphasize the potential of the GxxxG motif in the prevention of sporadic AD as well as FAD.

Neuroprotective mechanism conferred by 17beta-estradiol on the biochemical basis of Alzheimer's disease

Estrogen (17beta-estradiol) plays key regulatory roles in a variety of physiological and biological processes. Several lines of evidence also support its role as a protective factor in Alzheimer's disease; however, the basis of this effect is unclear. Here we show that an early-onset Alzheimer's disease transgenic mouse model expressing the double-mutant form of human amyloid precursor protein (APP); Swedish (K670N/M671L) and Indiana (V717F) undergoing treatment with 17beta-estradiol show significantly lower levels of APP processing through beta-secretase and enhanced alpha-secretase processing resulting in marked reductions of APP-CTFbeta, Abeta42 and plaque burden, along with increased levels of the non-amyloidogenic sAPPalpha. Moreover, 17beta-estradiol resulted in elevated brain levels of transthyretin, which inhibits aggregation of Abeta into plaques; though the insulin-degrading enzyme, which breaks down Abeta, was significantly reduced. These results illustrate a multifaceted effect of 17beta-estradiol on the biochemical basis of Alzheimer's disease, through effects on APP processing, Abeta levels and factors that affect its clearance and aggregation. Overall, these results support the need for further long-term longitudinal studies to elucidate consequences of menopause as well as hormone therapy on Alzheimer's disease, and explore its potential as a therapeutic avenue for the disease.

Dysregulation of dopamine transporters via dopamine D2 autoreceptors triggers anomalous dopamine efflux associated with attention-deficit hyperactivity disorder

The neurotransmitter dopamine (DA) modulates brain circuits involved in attention, reward, and motor activity. Synaptic DA homeostasis is primarily controlled via two presynaptic regulatory mechanisms, DA D(2) receptor (D(2)R)-mediated inhibition of DA synthesis and release, and DA transporter (DAT)-mediated DA clearance. D(2)Rs can physically associate with DAT and regulate DAT function, linking DA release and reuptake to a common mechanism. We have established that the attention-deficit hyperactivity disorder-associated human DAT coding variant Ala559Val (hDAT A559V) results in anomalous DA efflux (ADE) similar to that caused by amphetamine-like psychostimulants. Here, we show that tonic activation of D(2)R provides support for hDAT A559V-mediated ADE. We determine in hDAT A559V a pertussis toxin-sensitive, CaMKII-dependent phosphorylation mechanism that supports D(2)R-driven DA efflux. These studies identify a signaling network downstream of D(2)R activation, normally constraining DA action at synapses, that may be altered by DAT mutation to impact risk for DA-related disorders.

Cardiovascular dementia - a different perspective

The number of dementia patients has been growing in recent years and dementia represents a significant threat to aging people all over the world. Recent research has shown that the number of people affected by Alzheimer's disease (AD) and dementia is growing at an epidemic pace. The rapidly increasing financial and personal costs will affect the world's economies, health care systems, and many families. Researchers are now exploring a possible connection among AD, vascular dementia (VD), diabetes mellitus (type 2, T2DM) and cardiovascular diseases (CD). This correlation may be due to a strong association of cardiovascular risk factors with AD and VD, suggesting that these diseases share some biologic pathways. Since heart failure is associated with an increased risk of AD and VD, keeping the heart healthy may prove to keep the brain healthy as well. The risk for dementia is especially high when diabetes mellitus is comorbid with severe systolic hypertension or heart disease. In addition, the degree of coronary artery disease (CAD) is independently associated with cardinal neuropathological lesions of AD. Thus, the contribution of T2DM and CD to AD and VD implies that cardiovascular therapies may prove useful in preventing AD and dementia.

Cholinesterase inhibitors in Alzheimer's disease and Lewy body spectrum disorders: the emerging pharmacogenetic story

This review provides an update on the current state of pharmacogenetic research in the treatment of Alzheimer's disease (AD) and Lewy body disease (LBD) as it pertains to the use of cholinesterase inhibitors (ChEI). AD and LBD are first reviewed from clinical and pathophysiological perspectives. This is followed by a discussion of ChEIs used in the symptomatic treatment of these conditions, focusing on their unique and overlapping pharmacokinetic and pharmacodynamic profiles, which can be used to identify candidate genes for pharmacogenetics studies. The literature published to date is then reviewed and limitations are discussed. This is followed by a discussion of potential endophenotypes which may help to refine future pharmacogenetic studies of response and adverse effects to ChEIs.

Maternal transmission of Alzheimer's disease: prodromal metabolic phenotype and the search for genes

After advanced age, having a parent affected with Alzheimer's disease (AD) is the most significant risk factor for developing AD among cognitively normal (NL) individuals. Although rare genetic mutations have been identified among the early-onset forms of familial AD (EOFAD), the genetics of the more common forms of late-onset AD (LOAD) remain elusive. While some LOAD cases appear to be sporadic in nature, genetically mediated risk is evident from the familial aggregation of many LOAD cases. The patterns of transmission and biological mechanisms through which a family history of LOAD confers risk to the offspring are not known. Brain imaging studies using 2-[ (18) F]fluoro-2-deoxy-D-glucose positron emission tomography ((18)F-FDG PET) have shown that NL individuals with a maternal history of LOAD, but not with a paternal family history, express a phenotype characterised by a pattern of progressive reductions of brain glucose metabolism, similar to that in AD patients. As maternally inherited AD may be associated with as many as 20 per cent of the total LOAD population, understanding the causes and mechanisms of expression of this form of AD is of great relevance. This paper reviews known genetic mutations implicated in EOFAD and their effects on brain chemistry, structure and function; epidemiology and clinical research findings in LOAD, including in vivo imaging findings showing selective patterns of hypometabolism in maternally inherited AD; possible genetic mechanisms involved in maternal transmission of AD, including chromosome X mutations, mitochondrial DNA and imprinting; and genetic mechanisms involved in other neurological disorders with known or suspected maternal inheritance. The review concludes with a discussion of the potential role of brain imaging for identifying endophenotypes in NL individuals at risk for AD, and for directing investigation of potential susceptibility genes for AD.

A narrow and highly significant linkage signal for severe bipolar disorder in the chromosome 5q33 region in Latin American pedigrees

We previously reported linkage of bipolar disorder to 5q33-q34 in families from two closely related population isolates, the Central Valley of Costa Rica (CVCR) and Antioquia, Colombia (CO). Here we present follow up results from fine-scale mapping in large CVCR and CO families segregating severe bipolar disorder, BP-I, and in 343 population trios/duos from CVCR and CO. Employing densely spaced SNPs to fine map the prior linkage peak region increases linkage evidence and clarifies the position of the putative BP-I locus. We performed two-point linkage analysis with 1134 SNPs in an approximately 9 Mb region between markers D5S410 and D5S422. Combining pedigrees from CVCR and CO yields a LOD score of 4.9 at SNP rs10035961. Two other SNPs (rs7721142 and rs1422795) within the same 94 kb region also displayed LOD scores greater than 4. This linkage peak coincides with our prior microsatellite results and suggests a narrowed BP-I susceptibility regions in these families. To investigate if the locus implicated in the familial form of BP-I also contributes to disease risk in the population, we followed up the family results with association analysis in duo and trio samples, obtaining signals within 2 Mb of the peak linkage signal in the pedigrees; rs12523547 and rs267015 (P = 0.00004 and 0.00016, respectively) in the CO sample and rs244960 in the CVCR sample and the combined sample, with P = 0.00032 and 0.00016, respectively. It remains unclear whether these association results reflect the same locus contributing to BP susceptibility within the extended pedigrees.

Differential damage in the frontal cortex with aging, sporadic and familial Alzheimer's disease

In order to understand relationships between executive and structural deficits in the frontal cortex of patients within normal aging or Alzheimer's disease, we studied frontal pathological changes in young and old controls compared to cases with sporadic (AD) or familial Alzheimer's disease (FAD). We performed a semi-automatic computer assisted analysis of the distribution of beta-amyloid (Abeta) deposits revealed by Abeta immunostaining as well as of neurofibrillary tangles (NFT) revealed by Gallyas silver staining in Brodman areas 10 (frontal polar), 12 (ventro-infero-median) and 24 (anterior cingular), using tissue samples from 5 FAD, 6 sporadic AD and 10 control brains. We also performed densitometric measurements of glial fibrillary acidic protein, principal compound of intermediate filaments of astrocytes, and of phosphorylated neurofilament H and M epitopes in areas 10 and 24. All regions studied seem almost completely spared in normal old controls, with only the oldest ones exhibiting a weak percentage of beta-amyloid deposit and hardly any NFT. On the contrary, all AD and FAD cases were severely damaged as shown by statistically significant increased percentages of beta-amyloid deposit, as well as by a high number of NFT. FAD cases (all from the same family) had statistically more beta-amyloid and GFAP than sporadic AD cases in both areas 10 and 24 and statistically more NFT only in area 24. The correlation between the percentage of beta-amyloid and the number of NFT was significant only for area 24. Altogether, these data suggest that the frontal cortex can be spared by AD type lesions in normal aging, but is severely damaged in sporadic and still more in familial Alzheimer's disease. The frontal regions appear to be differentially vulnerable, with area 12 having the less amyloid burden, area 24 the less NFT and area 10 having both more amyloid and more NFT. This pattern of damage in frontal regions may represent a strong neuroanatomical support for the deterioration of attention and cognitive capacities as well as for the presence of emotional and behavioral troubles in AD patients.

Variability of AChE, BChE, and ChAT genes in the late-onset form of Alzheimer's disease and relationships with response to treatment with Donepezil and Rivastigmine

Several factors are believed to give rise to the late onset sporadic form of Alzheimer's disease (LOAD). We have studied the variation at the genes of three enzymes of the cholinergic system: acetylcholinesterase, butyrylcholinesterase, and choline acetyltransferase. The single nucleotide polymorphisms (SNPs) examined were: AChE rs2571598, BChE rs1355534, BChE rs1803274, and ChAT rs2177369. The sample for the case-control study was 471 LOAD patients aged 60 years or older, and 254 subjects with no neurodegenerative disorders as the control group. A significant difference in the genotype distribution between patients and controls was observed only for ChAT rs2177369, showing that the G/G genotype was to be considered a risk factor with respect to the G/A + A/A genotypes (odds ratio = 1.56; 95% Confidence Interval = 1.10-2.22; P = 0.01). Though indicating a significant association with AD onset, our results are far from definitive since contrast with the ones reported by other authors in a previous case-control study, and call for further investigations. Among patients, 171 took part in an observational study concerning the possible role of the genetic composition on the efficacy of treatment with Donepezil and Rivastigmine. We related the SNPs of the above cited genes with cognitive status measured by MMSE. Carrying an allele or a genotype of these SNPs does not seem to play a relevant role in the response to treatment with the two cholinesterase inhibitors, though some significant results were found associated with the AChE A/A genotype that had the best response when treated with Rivastigmine.

What is 'early onset dementia'?

There are two types of dementia with early onset: (i) presenile dementias; and (ii) senile dementias with early onset. Most patients who develop dementia before 65 years of age have Alzheimer's disease (AD). The remainder are likely to have vascular dementia (VaD), frontotemporal dementia, head injury, alcohol intoxication, or metabolic disorder. Presenile dementias, caused by frontotemporal lobar degeneration, progressive supranuclear palsy, and corticobasal degeneration, usually occur in patients of presenile and are rarely seen in patients of senile age. Although the factors responsible for the accelerated onset of the illness are not fully known, genetic abnormalities appear to be important in some types of presenile dementia, such as frontotemporal dementia with parkinsonism linked to chromosome 17. Conversely, senile dementias such as sporadic AD and VaD commonly occur in patients of senile age. These disorders may also occur in patients of presenile age, although less frequently. Alzheimer's disease was originally classified as a 'presenile dementia'. Since the 1980s, 'senile dementia of Alzheimer type' (SDAT) and 'Alzheimer's disease' have been considered to belong to the same pathological entity and both are now known as 'dementia of Alzheimer's type (DAT)' or merely 'Alzheimer's disease'. Rapid progression of cognitive impairment with neuropsychological syndromes and neurological symptoms has been considered a characteristic of early onset AD. However, recently, neurological symptoms such as spastic paraparesis, seizures, and myoclonic convulsions have been reported to occur infrequently in early onset AD, although language problems and visuospatial dysfunctions are common. There are at least three dominant genes that have been identified in cases of familial Alzheimer's disease with early onset, namely the amyloid precursor gene (APP), and the genes encoding presenilin 1 (PSEN1) and presenilin 2 (PSEN2). Therefore, genetic abnormalities are important factors contributing to the earlier onset of the illness. It is also important to investigate the pathophysiological mechanism in relation to genetic abnormalities, environmental factors, physical illnesses, and metabolic disturbances to understand the processes underlying the development of dementia with early onset.

A recessive mutation in the APP gene with dominant-negative effect on amyloidogenesis

beta-Amyloid precursor protein (APP) mutations cause familial Alzheimer's disease with nearly complete penetrance. We found an APP mutation [alanine-673-->valine-673 (A673V)] that causes disease only in the homozygous state, whereas heterozygous carriers were unaffected, consistent with a recessive Mendelian trait of inheritance. The A673V mutation affected APP processing, resulting in enhanced beta-amyloid (Abeta) production and formation of amyloid fibrils in vitro. Co-incubation of mutated and wild-type peptides conferred instability on Abeta aggregates and inhibited amyloidogenesis and neurotoxicity. The highly amyloidogenic effect of the A673V mutation in the homozygous state and its anti-amyloidogenic effect in the heterozygous state account for the autosomal recessive pattern of inheritance and have implications for genetic screening and the potential treatment of Alzheimer's disease.

Cortical development in the presenilin-1 null mutant mouse fails after splitting of the preplate and is not due to a failure of reelin-dependent signaling

Cortical development is disrupted in presenilin-1 null mutant (Psen1-/-) mice. Prior studies have commented on similarities between Psen1-/- and reeler mice. Reelin induces phosphorylation of Dab1 and activates the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Psen1 is known to modulate PI3K/Akt signaling and both known reelin receptors (apoER2 and VLDLR) are substrates for Psen1 associated gamma-secretase activity. The purpose of this study was to determine whether reelin signaling is disrupted in Psen1-/- mice. We show that, while Dab1 is hypophosphorylated late in cortical development in Psen1-/- mice, it is normally phosphorylated at earlier ages and reelin signaling is intact in Psen1-/- primary neuronal cultures. gamma-secretase activity was also not required for reelin-induced phosphorylation of Dab1. Unlike reeler mice the preplate splits in Psen1-/- brain. Thus cortical development in Psen1-/- mice fails only after splitting of the preplate and is not due to an intrinsic failure of reelin signaling.

Lithium may be useful in the prevention of Alzheimer's disease in individuals at risk of presenile familial Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia among older people. Presenile familial AD (FAD) and sporadic Alzheimer's disease (SAD) have identical brain lesions, containing senile plaques with beta-amyloid (Abeta) peptide and neurofibrillary tangles formed by hyperphosphorylation of a microtubule-associated protein known as tau. However, FAD and SAD differ in onset and genetic transmission. Unlike SAD, presenile FAD is transmitted as a pure autosomal dominant trait. The authors suggest that lithium could be used for AD prevention, particularly in individuals at risk of presenile FAD, which has early onset. Evidence supporting this hypothesis suggests that lithium decreases Abeta peptide production and inhibits the activity of glycogen synthase kinase-3 which induces aggregation of tau protein into tangles, and tau hyperphosphorylation. Prevalence of AD is lower in patients with chronic lithium treatment, which also increases brain-derived neurotrophic factor activity, so might prevent onset in patients at risk for AD. Several considerations are suggested for prevention trials: the effect of lithium could be evaluated in young animal models that express presenile FAD mutant genes; the time, dose, duration and monitoring of lithium therapy are considered; early phenotypes could be monitored for treatment effect; and some other agents, like valproic acid, could also be candidates for prevention.

Anomalous dopamine release associated with a human dopamine transporter coding variant

Dopamine (DA) signaling at synapses is tightly coordinated through opposing mechanisms of vesicular fusion-mediated DA release and transporter-mediated DA clearance. Altered brain DA signaling is suspected to underlie multiple brain disorders, including schizophrenia, Parkinson's disease, bipolar disorder, and attention-deficit hyperactivity disorder (ADHD). We identified a pedigree containing two male children diagnosed with ADHD who share a rare human DA transporter (DAT; SLC6A3) coding variant, Ala559Val. Among >1000 control and affected subjects, the Val559 variant has only been isolated once previously, in a female subject with bipolar disorder. Although hDAT Ala559Val supports normal DAT protein and cell surface expression, as well as normal DA uptake, the variant exhibits anomalous DA efflux from DA-loaded cells. We also demonstrate that hDAT Ala599Val exhibits increased sensitivity to intracellular Na(+), but not intracellular DA, and displays exaggerated DA efflux at depolarized potentials. Remarkably, the two most common ADHD medications, amphetamine and methylphenidate, both block hDAT Ala559Val-mediated DA efflux, whereas these drugs have opposite actions at wild-type hDAT. Our findings reveal that DA efflux, typically associated with amphetamine-like psychostimulants, can be produced through a heritable change in hDAT structure. Because multiple gene products are known to coordinate to support amphetamine-mediated DA efflux, the properties of hDAT Ala559Val may have broader significance in identifying a new mechanism through which DA signaling disorders arise. Additionally, they suggest that block of inappropriate neurotransmitter efflux may be an unsuspected mechanism supporting the therapeutic actions of existing transporter-directed medications.

Presenilin 1 interacts with acetylcholinesterase and alters its enzymatic activity and glycosylation

Presenilin 1 (PS1) plays a critical role in the gamma-secretase processing of the amyloid precursor protein to generate the beta-amyloid peptide, which accumulates in plaques in the pathogenesis of Alzheimer's disease (AD). Mutations in PS1 cause early onset AD, and proteins that interact with PS1 are of major functional importance. We report here the coimmunoprecipitation of PS1 and acetylcholinesterase (AChE), an enzyme associated with amyloid plaques. Binding occurs through PS1 N-terminal fragment independent of the peripheral binding site of AChE. Subcellular colocalization of PS1 and AChE in cultured cells and coexpression patterns of PS1 and AChE in brain sections from controls and subjects with sporadic or familial AD indicated that PS1 and AChE are located in the same intracellular compartments, including the perinuclear compartments. A PS1-A246E pathogenic mutation expressed in transgenic mice leads to decreased AChE activity and alteration of AChE glycosylation and the peripheral binding site, which may reflect a shift in protein conformation and disturbed AChE maturation. In both the transgenic mice and humans, mutant PS1 impairs coimmunoprecipitation with AChE. The results indicate that PS1 can interact with AChE and influence its expression, supporting the notion of cholinergic-amyloid interrelationships.

Motor impairment in Alzheimer's disease and transgenic Alzheimer's disease mouse models

In this commentary, we accent the accumulating evidence for motor impairment as a common feature of early Alzheimer's disease (AD) pathology. In addition, we summarize the state of knowledge on this phenotype in experimental mouse models, expressing AD-associated genes like tau or amyloid precursor protein.

Coenzyme Q10 attenuates beta-amyloid pathology in the aged transgenic mice with Alzheimer presenilin 1 mutation

One of the neuropathological features of Alzheimer's disease (AD) is the deposition of senile plaques containing beta-amyloid (A beta). There is limited evidence for the treatment to arrest A beta pathology of AD. In our present study, we tested the effect of coenzyme Q10 (CoQ10), an endogenous antioxidant and a powerful free radical scavenger, on A beta in the aged transgenic mice overexpressing Alzheimer presenilin 1-L235P (leucine-to-proline mutation at codon 235, 16-17 months old). The treatment by feeding the transgenic mice with CoQ10 for 60 days (1,200 mg kg(-1) day(-1)) partially attenuated A beta overproduction and intracellular A beta deposit in the cortex of the transgenic mice compared with the age-matched untreated transgenic mice. Meanwhile, an increased oxidative stress reaction was detected as evidenced by elevated level of malondialdehyde (MDA) and decreased activity of superoxide dismutase (SOD) in the transgenic mice relative to the wild-type mice, and supplementation of CoQ10 partially decreased MDA level and upregulated the activity of SOD. The results indicate that oxidative stress is enhanced in the brain of the transgenic mice, that this enhancement may further promote A beta 42 overproduction in a vicious formation, and that CoQ10 would be beneficial for the therapy of AD.

Advances on the understanding of the origins of synaptic pathology in AD

Although Alzheimer's disease (AD) was first discovered a century ago, we are still facing a lack of definitive diagnosis during the patient's lifetime and are unable to prescribe a curative treatment. However, the past 10 years have seen a "revamping" of the main hypothesis about AD pathogenesis and the hope to foresee possible treatment. AD is no longer considered an irreversible disease. A major refinement of the classic beta-amyloid cascade describing amyloid fibrils as neurotoxins has been made to integrate the key scientific evidences demonstrating that the first pathological event occurring in AD early stages affects synaptic function and maintenance. A concept fully compatible with synapse loss being the best pathological correlate of AD rather than other described neuropathological hallmarks (amyloid plaques, neurofibrillary tangles or neuronal death). The notion that synaptic alterations might be reverted, thus offering a potential curability, was confirmed by immunotherapy experiments targeting beta-amyloid protein in transgenic AD mice in which cognitive functions were improved despite no reduction in the amyloid plaques burden. The updated amyloid cascade now integrates the synapse failure triggered by soluble Abeta-oligomers. Still no consensus has been reached on the most toxic Abeta conformations, neither on their site of production nor on their extra- versus intra-cellular actions. Evidence shows that soluble Abeta oligomers or ADDLs bind selectively to neurons at their synaptic loci, and trigger major changes in synapse composition and morphology, which ultimately leads to dendritic spine loss. However, the exact mechanism is not yet fully understood but is suspected to involve some membrane receptor(s).

Positron Emission Tomography Diagnosis of Alzheimer's Disease

Positron emission tomography (PET) imaging of [18F]-2-fluoro-2-deoxy-D-glucose (FDG) is accurate in the early detection of Alzheimer's disease (AD) and in the differentiation of AD from the other causes of dementia. FDG-PET imaging is available widely and performed easily. Different patterns of abnormality with the various causes of dementia are well described. Semiquantitative methods of image interpretation are available. Medicare covers FDG-PET imaging for the narrow indication of differentiation of possible AD from frontotemporal dementia.

Amyloid beta peptides and glutamatergic synaptic dysregulation

Alzheimer's disease (AD) is a major neurodegenerative disorder in which overproduction and accumulation of amyloid beta (Abeta) peptides result in synaptic dysfunction. Recent reports strongly suggest that in the initial stages of AD glutamate receptors are dysregulated by Abeta accumulation resulting in disruption of glutamatergic synaptic transmission which parallels early cognitive deficits. In the presence of Abeta, 2-amino-3-(3-hydoxy-5-methylisoxazol-4-yl) propionic acid (AMPA) glutamate receptor function is disrupted and the surface expression is reduced. Abeta has also been shown to modulate N-methyl-d-aspartate receptors (NMDARs) and metabotropic glutamate receptors. The Abeta mediated glutamate receptor modifications can lead to synaptic dysfunction resulting in excitotoxic neurodegeneration during the progression of AD. This review discusses the recent findings that glutamatergic signaling could be compromised by Abeta induced modulation of synaptic glutamate receptors in specific brain regions.

Gene variations in GSTM3 are a risk factor for Alzheimer's disease

Oxidative stress is a relevant pathomechanism in Alzheimer's disease (AD) and gene variations in the glutathione S-transferase M3 gene (GSTM3), involved in the detoxification of oxygen radicals, might influence the risk of AD. We investigated the effect of three polymorphisms in GSTM3: rs1332018 (C/A); rs1799735 (del/AGG); rs7483 (G/A), on the risk of AD in 363 AD patients and 358 healthy controls. Single marker association analyses revealed that the AGG/AGG genotype of the GSTM3 rs1799735 (del/AGG) polymorphism was associated with an increased risk of AD (p=0.05), especially in the group of APOE4-allele non-carriers (p=0.004; OR=2.07). Examination of the haplotypes identified a two-marker haplotype (C/AGG) consisting of rs1332018 (C/A) and rs1799735 (del/AGG) to increase the risk of AD (p=0.029), this effect was also most prevalent in APOE4-allele non-carriers (p=0.009; OR=1.95). The population attributable risk of this haplotype in APOE4-allele non-carriers was 32.2%. Our results suggest that there is a group of AD patients in which variations in metabolism of oxidative stress play an important role.

Modulation of Abeta generation by small ubiquitin-like modifiers does not require conjugation to target proteins

The sequential processing of the APP (amyloid precursor protein) by the beta- and gamma-secretase and generation of the Abeta (amyloid-beta) peptide is a primary pathological factor in AD (Alzheimer's disease). Regulation of the processing or turnover of these proteins represents potential targets for the development of AD therapies. Sumoylation is a process by which SUMOs (small ubiquitin-like modifiers) are covalently conjugated to target proteins, resulting in a number of functional consequences. These include regulation of protein-protein interactions, intracellular trafficking and protein stability, which all have the potential to impact on several aspects of the amyloidogenic pathway. The present study examines the effects of overexpression and knockdown of the major SUMO isoforms (SUMO1, 2 and 3) on APP processing and the production of Abeta peptides. SUMO3 overexpression significantly increased Abeta40 and Abeta42 secretion, which was accompanied by an increase in full-length APP and its C-terminal fragments. These effects of SUMO3 were independent of its covalent attachment or chain formation, as mutants lacking the motifs responsible for SUMO chain formation or SUMO conjugation led to similar changes in Abeta. SUMO3 overexpression also up-regulated the expression of the transmembrane protease BACE (beta-amyloid-cleaving enzyme), but failed to affect levels of several other unrelated proteins. Suppression of SUMO1 or combined SUMO2+3 by RNA interference did not affect APP levels or Abeta production. These findings confirm a specific effect of SUMO3 overexpression on APP processing and the production of Abeta peptides but also suggest that endogenous sumoylation is not essential and likely plays an indirect role in modulating the amyloid processing pathway.

Interaction between the APOE epsilon4 allele and the APH-1b c + 651T > G SNP in Alzheimer's disease

The gamma-secretase complex is a multimeric aspartyl protease which plays a pivotal role in the production of amyloid beta-peptide, the main component of senile plaques in Alzheimer's disease (AD). APH-1a and APH-1b have been recently identified as important subunits of the gamma-secretase complex. We previously studied sequence variations in both genes and their association with AD in a small Italian population. The rare polymorphism c + 651T > G in APH-1b showed a possible interaction with the Apolipoprotein E (APOE) epsilon4 allele in the AD population sample. We extended our genetic analysis to 449 AD patients and 435 controls and, in AD cases, we found a significant interaction (P=0.001) between the allelic variants in the two genes, resulting in a marked increase of the relative risk for AD (OR=28.6). Despite the amino acid substitution does not seem to modify either the intracellular localization or the half-life of APH-1b protein, these data suggest that a cooperative mechanism involving APOE and APH-1b plays a role in the susceptibility to develop AD.

A mutation screening by DHPLC of PSEN1 and APP genes reveals no significant variation associated with the sporadic late-onset form of Alzheimer's disease

Alzheimer's disease (AD), the most common cause of dementia in the elderly, is usually divided into familial and sporadic forms, according to family history. The familial form has often been reportedly caused by mutations in amyloid precursor protein (APP), presenilin-1 (PSEN1), or presenilin-2 (PSEN2) genes, whereas the genetic component for the sporadic form is less clear. We carried out mutation screening in exons 16 and 17 of APP, and in exons 3, 4, 5, 6, 7, 10 of PSEN1 genes in patients with the sporadic late-onset form of AD (LOAD). The aim of this study was to ascertain whether any variation in these genes, besides that of the well-known apolipoprotein E common polymorphism, could be involved in the onset of the disease. To search for the single nucleotide substitutions, we examined 172 LOAD patients by the denaturing high-performance liquid chromatography (DHPLC) technique. Only one same-sense mutation in exon 4 of PSEN1 gene (N32) was observed in this patient group. We concluded that the variation in the screened exons of the APP and PSEN1 genes, reportedly associated with familial AD, is not present in LOAD.

Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina

Accumulating evidence indicates that mutations in the presenilin 1 (PS1) gene are responsible for most cases of familial Alzheimer's disease (AD). Although its biological functions are not yet fully understood, it appears that PS1 plays a role in the processing and trafficking of the amyloid precursor protein (APP). However, little is known about factors that are involved in regulating the metabolism of PS1 especially in relation to AD pathology. In this study, we have examined the effect of optic nerve crush, intravitreal injection of the inflammatory agent lipopolysaccharide (LPS) or injection of amyloid beta(1-42) (A beta(1-42)) on the expression and processing of PS1 in the rat retina. We found that 48 h after injection of A beta(1-42) there was a dramatic alteration in the banding pattern of PS1 on Western blots, as indicated by marked changes in the levels of expression of some of its C- and N-terminal fragments in retinal homogenates. These results suggest an A beta(1-42)-induced potentiation of a non-specific stress-related but inflammation-independent alteration of processing of PS1 in this in vivo model.

Excess of nicastrin in brain results in heterozygosity having no effect on endogenous APP processing and amyloid peptide levels in vivo

Nicastrin is an integral member of PS-complexes that perform gamma-secretase cleavage of numerous type I membrane proteins including amyloid precursor protein that underlies Alzheimer's disease; thus, diminishing gamma-secretase activity by reducing levels of functional PS-complexes is suggested as a possible preventative/therapeutic avenue for the disease. One means of reducing PS-complex activity entails decreasing the levels of one or more of its components, such as nicastrin, which is fundamental to its assembly. Two previous studies detailing the effects of decreased nicastrin on gamma-secretase cleavage of APP in nicastrin heterozygous mouse fibroblast, which express relatively low levels of endogenous nicastrin compared to neurons, were contradictory. One report documented a 50% reduction in gamma-secretase cleavage of APP while the second showed markedly higher levels of this activity. Here we report that brains of heterozygous nicastrin mice show no difference in levels of APP gamma-secretase cleavage, APP C-terminal fragments or beta-amyloid peptides, compared to wild-type. This result is explained by the levels of nicastrin protein and functional presenilin complexes being similar between the heterozygous and wild-type brains, though nicastrin mRNA levels were diminished appropriately in the former. These in vivo results indicate that nicastrin mRNA and its immature protein are likely in overabundance in neurons and not limiting for assembly of PS-complexes, and that a 50% reduction of its mRNA or protein production would not affect APP processing, in contrast to fibroblast. Thus, partial reduction (maintaining a level above 50% of normal) of brain nicastrin would likely not be efficacious in reducing functional PS-complexes and gamma-secretase activity as a therapeutic strategy for Alzheimer's disease.

Involvement of the nitric oxide pathway in synaptic dysfunction following amyloid elevation in Alzheimer's disease

Amyloid-beta (Abeta), a peptide thought to play a crucial role in Alzheimer's disease (AD), has attracted scientific interest with the aim of characterizing the mechanisms by which it is involved in AD pathogenesis. Abeta has been found to markedly impair hippocampal long-term potentiation (LTP), a widely studied cellular model of synaptic plasticity that is thought to underlie learning and memory. The overall purpose of this review is to define the role of the nitric oxide (NO)/cGMP/cAMP-regulatory element binding (CREB) pathway in beta-amyloid-induced changes of basal neurotransmission and synaptic plasticity in the hippocampus, a structure within the temporal lobe of the brain critical for memory storage.

Drug discovery in dementia: the role of rodent models

Recent advances in the understanding of the pathophysiological mechanisms underlying Alzheimer's disease have pointed to novel strategies for drug development. Animal models have contributed considerably to these advances, and will have a key role in the evaluation of therapeutics that could have the potential not just to alleviate the dementia associated with Alzheimer's disease, but to modify the disease process. Here, we summarize and critically evaluate current rodent models of dementia, and discuss their role in drug discovery and development.

Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis

Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.

Influence of lysosomal acid lipase polymorphisms on chromosome 10 on the risk of Alzheimer's disease and cholesterol metabolism

Linkage analyses have identified a possible hot spot for a late-onset Alzheimer's disease (LOAD) risk gene on chromosome 10q21-22 and 10q25. It was also shown that cholesterol metabolism is involved in the pathogenic mechanisms of AD. The gene of lysosomal acid lipase (LIPA) is located next to the putative hot spot on chromosome 10. Its protein is involved in cholesterol metabolism and responsible for catalysing the hydrolysis of cholesteryl esters and triglycerides inside the lysosome. Previous publications reported controversial results on the role of LIPA polymorphisms on the risk of LOAD. We investigated two LIPA polymorphisms (rs1051338 and rs2297472) for their putative effect on the risk of LOAD in a homogenous sample of German origin. Genotypes of the investigated polymorphisms in AD patients and controls were compared. Also the effect of the LIPA gene polymorphisms on plasma cholesterol levels and 24S-hydroxycholesterol/cholesterol ratios on AD patients were investigated. None of the observed polymorphisms showed a significant influence on the risk of AD. We found that LIPA exon 2 polymorphism (rs1051338) influenced plasma 24S-hydroxycholesterol/cholesterol ratios in AD patients where carriers of the C/C allele presented with higher ratios than heterozygote carriers of the LIPA allele. Even though the biological function and gene location of LIPA on chromosome 10 suggest that LIPA might be a candidate for an AD risk gene, our results revealed that polymorphisms in LIPA did not influence the risk of AD in our study.

Loss of nicastrin elicits an apoptotic phenotype in mouse embryos

Nicastrin is a member of the high molecular weight presenilin complex that plays a central role in gamma-secretase cleavage of numerous type-1 membrane-associated proteins required for cell signaling, proliferation and lineage development. We have generated a nicastrin-null mouse line by disruption of exon 3. Similar to previously described nicastrin-null mice, these animals demonstrate severe growth retardation, mortality beginning at embryonic age 10.5 days, and marked developmental abnormalities indicative of a severe Notch phenotype. Preceding their mortality, 10.5-day-old nicastrin-null embryos were found to also exhibit specific apoptosis within regions showing profound deformities, particularly in the developing heart and brain. This result suggests that complete disruption of presenilin complexes elicits programmed cell death, in addition to a Notch phenotype, which may contribute to the developmental abnormalities and embryonic mortality of nicastrin-null mice and possibly neurodegeneration in Alzheimer's disease.

Transcriptional regulation of PEN-2, a key component of the gamma-secretase complex, by CREB

Gamma-secretase, which is responsible for the intramembranous cleavage of Alzheimer's beta-amyloid precursor protein (APP), the signaling receptor Notch, and many other substrates, is a multiprotein complex consisting of at least four components: presenilin (PS), nicastrin, APH-1, and PEN-2. Despite the fact that PEN-2 is known to mediate endoproteolytic cleavage of full-length PS and APH-1 and nicastrin are required for maintaining the stability of the complex, the detailed physiological function of each component remain elusive. Unlike that of PS, the transcriptional regulation of PEN-2, APH-1, and nicastrin has not been investigated. Here, we characterized the upstream regions of the human PEN-2 gene and identified a 238-bp fragment located 353 bp upstream of the translational start codon as the key region necessary for the promoter activity. Further analysis revealed a CREB binding site located in the 238-bp region that is essential for the transcriptional activity of the PEN-2 promoter. Mutation of the CREB site abolished the transcriptional activity of the PEN-2 promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation analysis showed the binding of CREB to the PEN-2 promoter region both in vitro and in vivo. Activation of the CREB transcriptional factor by forskolin dramatically promoted the expression of PEN-2 mRNA and protein, whereas the other components of the gamma-secretase complex remained unaffected. Forskolin treatment slightly increases the secretion of soluble APPalpha and Abeta without affecting Notch cleavage. These results demonstrate that expression of PEN-2 is regulated by CREB and suggest that the specific control of PEN-2 expression may imply additional physiological functions uniquely assigned to PEN-2.

Alzheimer's disease and post-operative cognitive dysfunction

Alzheimer's disease (AD), an insidious and progressive neurodegenerative disorder accounting for the vast majority of dementia, is characterized by global cognitive decline and the robust accumulation of amyloid deposits and neurofibrillary tangles in the brain. This review article is based on the currently published literature regarding molecular studies of AD and the potential involvement of AD neuropathogenesis in post-operative cognitive dysfunction (POCD). Genetic evidence, confirmed by neuropathological and biochemical studies, indicates that excessive beta-amyloid protein (Abeta) generated from amyloidogenic processing of the beta-amyloid precursor protein (APP) plays a fundamental role in the AD neuropathogenesis. Abeta is produced from APP by beta-secretase, and then gamma-secretase complex, consisting of presenilins, nicastrin (NCSTN), APH-1 and PEN-2. Additionally, Abeta clearance and APP adaptor proteins can contribute to AD neuropathogenesis via affecting Abeta levels. Finally, cellular apoptosis may also be involved in AD neuropathogenesis. Surgery and anesthesia can cause cognitive disorders, especially in elderly patients. Even the molecular mechanisms underlying these disorders are largely unknown; several perioperative factors such as hypoxia, hypocapnia and anesthetics may be associated with AD and render POCD via trigging AD neuropathogenesis. More studies to assess the potential relationship between anesthesia/surgery and AD dementia are, therefore, urgently needed.

Polymorphisms of the cholesterol 24-hydroxylase (CYP46A1) gene and the risk of Alzheimer's disease in a Chinese population

BACKGROUND

An increasing number of studies have suggested a link between cholesterol metabolism and Alzheimer's disease (AD), which may be mediated by its effect on amyloid processing. Intracranial cholesterol is primarily eliminated into the bloodstream through conversion into 24-hydroxycholesterol by the enzyme cholesterol 24-hydroxylase (encoded by the CYP46A1 gene). CYP46A1 is an essential gene modulating cholesterol metabolism in the brain.

METHOD

To investigate whether polymorphisms in the CYP46A1 gene modulate the risk of AD, we studied four common polymorphisms (IVS1-192, IVS2-150, IVS3-128 and IVS4-122) in 182 Chinese AD patients and 179 age-matched healthy Chinese subjects.

RESULTS AND CONCLUSION

We found that the IVS3-128 polymorphism was associated with the risk of AD (p < 0.05). Subjects homozygous for the C alleles were protected from AD with an adjusted odds ratio (OR) of 1.53 [95% confidence interval (95% CI) 0.98-2.37, p = 0.047]. However, another minor allele, IVS1-192 C, was more prevalent in the AD group and was associated with an increased risk. Haplotype analysis revealed that two of the eight common haplotypes formed by the four polymorphisms were rarely found in the AD group, suggesting a protective effect of these two haplotypes (GTCA and CCTA). The results supported the involvement of the CYP46A1 gene and cholesterol metabolism in the pathogenesis of AD.

Aging sensitizes toward ROS formation and lipid peroxidation in PS1M146L transgenic mice

Mutations in the presenilins (PS) account for the majority of familial Alzheimer disease (FAD) cases. To test the hypothesis that oxidative stress can underlie the deleterious effects of presenilin mutations, we analyzed lipid peroxidation products (4-hydroxynonenal (HNE) and malondialdehyde) and antioxidant defenses in brain tissue and levels of reactive oxygen species (ROS) in splenic lymphocytes from transgenic mice bearing human PS1 with the M146L mutation (PS1M146L) compared to those from mice transgenic for wild-type human PS1 (PS1wt) and nontransgenic littermate control mice. In brain tissue, HNE levels were increased only in aged (19-22 months) PS1M146L transgenic animals compared to PS1wt mice and not in young (3-4 months) or middle-aged mice (13-15 months). Similarly, in splenic lymphocytes expressing the transgenic PS1 proteins, mitochondrial and cytosolic ROS levels were elevated to 142.1 and 120.5% relative to controls only in cells from aged PS1M146L animals. Additionally, brain tissue HNE levels were positively correlated with mitochondrial ROS levels in splenic lymphocytes, indicating that oxidative stress can be detected in different tissues of PS1 transgenic mice. Antioxidant defenses (activities of antioxidant enzymes Cu/Zn-SOD, GPx, or GR) or susceptibility to in vitro oxidative stimulation was unaltered. In summary, these results demonstrate that the PS1M146L mutation increases mitochondrial ROS formation and oxidative damage in aged mice. Hence, oxidative stress caused by the combined effects of aging and PS1 mutations may be causative for triggering neurodegenerative events in FAD patients.

Formation of tau inclusions in knock-in mice with familial Alzheimer disease (FAD) mutation of presenilin 1 (PS1)

Mutations in the presenilin 1 (PS1) gene are responsible for the early onset of familial Alzheimer disease (FAD). Accumulating evidence shows that PS1 is involved in gamma-secretase activity and that FAD-associated mutations of PS1 commonly accelerate Abeta(1-42) production, which causes Alzheimer disease (AD). Recent studies suggest, however, that PS1 is involved not only in Abeta production but also in other processes that lead to neurodegeneration. To better understand the causes of neurodegeneration linked to the PS1 mutation, we analyzed the development of tau pathology, another key feature of AD, in PS1 knock-in mice. Hippocampal samples taken from FAD mutant (I213T) PS1 knock-in mice contained hyperphosphorylated tau that reacted with various phosphodependent tau antibodies and with Alz50, which recognizes the conformational change of PHF tau. Some neurons exhibited Congo red birefringence and Thioflavin T reactivity, both of which are histological criteria for neurofibrillary tangles (NFTs). Biochemical analysis of the samples revealed SDS-insoluble tau, which under electron microscopy examination, resembled tau fibrils. These results indicate that our mutant PS1 knock-in mice exhibited NFT-like tau pathology in the absence of Abeta deposition, suggesting that PS1 mutations contribute to the onset of AD not only by enhancing Abeta(1-42) production but by also accelerating the formation and accumulation of filamentous tau.

Presenilins in the developing, adult, and aging cerebral cortex

Mutations in presenilins are the major cause of familial Alzheimer disease. The involvement of presenilins in the pathogenesis of Alzheimer disease, therefore, has been the subject of intense investigation during the past decade. Genetic analysis of phenotypes associated with presenilin mutations in invertebrate and vertebrate systems has greatly advanced our understanding of the in vivo functions of presenilins. In this review, the authors will summarize the current understanding of presenilin function, with an emphasis on the mammalian cerebral cortex. During development, presenilins play crucial roles in the maintenance of neural progenitor cell proliferation, the temporal control of neuronal differentiation, the survival of Cajal-Retzius neurons, and proper neuronal migration in the developing cerebral cortex. Analysis of presenilin function in the adult cerebral cortex has revealed essential roles for presenilins in synaptic plasticity, long-term memory, and neuronal survival. The authors will also discuss the molecular mechanisms through which presenilins may mediate these functions, including the Notch, CREB, and NMDA receptor-mediated signaling pathways. These diverse functions of presenilins in cortical development and function and neuronal survival have important implications for the pathogenesis of neurodegenerative dementia.

Sequence variation in the human dopamine transporter gene in children with attention deficit hyperactivity disorder

The activity of the presynaptic dopamine (DA) transporter (DAT) is critical in mediating the magnitude and duration of dopaminergic signaling in the brain. Multiple genetic studies have found an association between attention deficit hyperactivity disorder (ADHD) and a variable number tandem repeat (VNTR) in the 3'-untranslated region (3'VNTR) of the hDAT gene (SLC6A3), however none of these studies examined the hDAT coding region for polymorphisms. Thus, we sought evidence of polymorphisms in hDAT, focusing on the coding region and splice junctions, utilizing genomic DNA from children diagnosed with ADHD. Two separate ADHD cohorts (N=70 and N=42) were screened and sampled for both status of the 3'VNTR and for common/novel genomic variants. We found evidence of increased DAT variation in African-American subjects as well as in predominantely hyperactive-impulsive probands. Cumulatively, multiple hDAT sequence variants were identified, including five novel variants, as well as one nonsynonymous single nucleotide polymorphism (SNP), converting Ala559 to Val (A559V). A559V was identified in two Caucasian male siblings with ADHD and both subjects were homozygous for the ADHD-associated, 10-repeat 3'VNTR allele. Interestingly, the A559V variant was previously identified in a subject with bipolar disorder [. Molecular Psychiatry 5, 275], a psychiatric disorder that has a significant number of overlapping symptoms with ADHD.

Positron Emission Tomography Diagnosis of Alzheimer's Disease

Positron emission tomography (PET) imaging of [18F]-2-fluoro-2-deoxy-D-glucose (FDG) is accurate in the early detection of Alzheimer's disease (AD) and in the differentiation of AD from the other causes of dementia. FDG-PET imaging is available widely and performed easily. Different patterns of abnormality with the various causes of dementia are well described. Semiquantitative methods of image interpretation are available. Medicare covers FDG-PET imaging for the narrow indication of differentiation of possible AD from frontotemporal dementia.