Association study of three polymorphisms of TGF-beta1 gene with Alzheimer's disease

Inflammatory Cytokines and Alzheimer's Disease: A Review from the Perspective of Genetic Polymorphisms

Neuroinflammatory processes are a central feature of Alzheimer's disease (AD) in which microglia are over-activated, resulting in the increased production of pro-inflammatory cytokines. Moreover, deficiencies in the anti-inflammatory system may also contribute to neuroinflammation. Recently, advanced methods for the analysis of genetic polymorphisms have further supported the relationship between neuroinflammatory factors and AD risk because a series of polymorphisms in inflammation-related genes have been shown to be associated with AD. In this review, we summarize the polymorphisms of both pro- and anti-inflammatory cytokines related to AD, primarily interleukin-1 (IL-1), IL-6, tumor necrosis factor alpha, IL-4, IL-10, and transforming growth factor beta, as well as their functional activity in AD pathology. Exploration of the relationship between inflammatory cytokine polymorphisms and AD risk may facilitate our understanding of AD pathogenesis and contribute to improved treatment strategies.

The impact of metabotropic glutamate receptors into active neurodegenerative processes: A "dark side" in the development of new symptomatic treatments for neurologic and psychiatric disorders

Metabotropic glutamate (mGlu) receptor ligands are under clinical development for the treatment of CNS disorders with high social and economic burden, such as schizophrenia, major depressive disorder (MDD), and Parkinson's disease (PD), and are promising drug candidates for the treatment of Alzheimer's disease (AD). So far, clinical studies have shown symptomatic effects of mGlu receptor ligands, but it is unknown whether these drugs act as disease modifiers or, at the opposite end, they accelerate disease progression by enhancing neurodegeneration. This is a fundamental issue in the treatment of PD and AD, and is also an emerging theme in the treatment of schizophrenia and MDD, in which neurodegeneration is also present and contribute to disease progression. Moving from in vitro data and preclinical studies, we discuss the potential impact of drugs targeting mGlu2, mGlu3, mGlu4 and mGlu5 receptor ligands on active neurodegeneration associated with AD, PD, schizophrenia, and MDD. We wish to highlight that our final comments on the best drug candidates are not influenced by commercial interests or by previous or ongoing collaborations with drug companies. This article is part of the Special Issue entitled 'Metabotropic Glutamate Receptors, 5 years on'.

Potential neuroprotective role of transforming growth factor β1 (TGFβ1) in the brain

TGFβ1 is a growth factor that is known to be expressed in most neurodegenerative diseases and after vascular accidents in the brain. TGFβ1 downregulates the activity of activated microglia and promotes astrogliosis. It also prevents cell death by a known mechanism dependant on astrocytes and the secretion of the plasminogen activator inhibitor 1 (PAI-1). This mechanism can provide light on what is the mechanism of action of TGFβ1 as a protective factor and it can provide the pharmacological principles in which this pathway could be used with therapeutic purposes. TGFβ1 is upregulated in most neurodegenerative diseases, however, its expression appears dramatically blocked in Huntington's disease, the fastest of those diseases in progress after the onset. This fact suggests that TGFβ1 slows down the neurodegenerative process, preventing tissue damage and neural apoptotic death. However, the exact details of TGFβ1 action are still unknown and the physiological roles on the diseases are still mysterious. Interestingly, all the data regarding the roles of TGFβ1 in health and disease have been also confirmed with the use of transgenic knockouts and TGFβ1 overexpressing mice. What possibly came as a surprise from the study of TGFβ1 overexpressing models is that combining its neuroprotective and antiproliferative effects, this cytokine generates a significant disruption in the hippocampal circuitry with its consequent learning and memory deficit.

Role of the Transforming-Growth-Factor-β1 Gene in Late-Onset Alzheimer's Disease: Implications for the Treatment

Late-onset Alzheimer's disease (LOAD) is the most common form of dementia in the elderly. LOAD has a complex and largely unknown etiology with strong genetic determinants. Genetics of LOAD is known to involve several genetic risk factors among which the Apolipoprotein E (APOE) gene seems to be the major recognized genetic determinant. Recent efforts have been made to identify other genetic factors involved in the pathophysiology of LOAD such as genes associated with a deficit of neurotrophic factors in the AD brain. Genetic variations of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), and transforming-growth-factor-β1 (TGF-β1) are known to increase the risk to develop LOAD and have also been related to depression susceptibility in LOAD. Transforming-Growth-Factor-β1 (TGF-β1) is a neurotrophic factor that exerts neuroprotective effects against ß-amyloid-induced neurodegeneration. Recent evidence suggests that a specific impairment in the signaling of TGF-β is an early event in the pathogenesis of AD. TGF-β1 protein levels are predominantly under genetic control, and the TGF-β1 gene, located on chromosome 19q13.1–3, con-tains several single nucleotide polymorphisms (SNPs) upstream and in the transcript region, such as the SNP at codon +10 (T/C) and +25 (G/C), which is known to influence the level of expression of TGF-β1. In the present review, we summarize the current literature on genetic risk factors for LOAD, focusing on the role of the TGF-β1 gene, finally discussing the possible implications of these genetic studies for the selection of patients eligible for neuroprotective strategies in AD.

The CC genotype of transforming growth factor-β1 increases the risk of late-onset Alzheimer's disease and is associated with AD-related depression

Transforming growth factor-β1 (TGF-β1) is a neurotrophic factor that exerts neuroprotective effects against β-amyloid-induced neurodegeneration. Recently, a specific impairment of the TGF-β1 signaling pathway has been demonstrated in Alzheimer's disease (AD) brain. TGF-β1 is also involved in the pathogenesis of depressive disorders, which may occur in 30-40% of AD patients. The TGF-β1 gene contains single nucleotide polymorphisms (SNPs) at codon +10 (T/C) and +25 (G/C), which are known to influence the level of expression of TGF-β1. We investigated TGF-β1 +10 (T/C) and +25 (G/C) SNPs and allele frequencies in 131 sporadic AD patients and in 135 healthy age- and sex-matched controls. Genotypes of the TGF-β1 SNPs at codon +10 (T/C) and +25 (G/C) did not differ between AD patients and controls, whereas the allele frequencies of codon +10 polymorphism showed a significant difference (P = 0.0306). We also found a different distribution of the +10 (C/C) phenotype (continuity-corrected χ(2) test with one degree of freedom = 4.460, P = 0.0347) between late onset AD (LOAD) patients and controls (P = 0.0126), but not between early onset AD (EOAD) patients and controls. In addition, the presence of the C/C genotype increased the risk of LOAD regardless of the status of apolipoprotein E4 (odds ratio [OR] = 2.34; 95% CI = 1.19-4.59). Compared to patients bearing the T/T and C/T polymorphisms, LOAD TGF-β1 C/C carriers also showed > 5-fold risk to develop depressive symptoms independently of a history of depression (OR = 5.50; 95% CI = 1.33-22.69). An association was also found between the TGF-β1 C/C genotype and the severity of depressive symptoms (HAM-D(17) ≥ 14) (P < 0.05). These results suggest that the CC genotype of the TGF-β1 gene increases the risk to develop LOAD and is also associated with depressive symptoms in AD.

Non-apolipoprotein E and apolipoprotein E genetics of sporadic Alzheimer's disease

The genetic epidemiology of sporadic Alzheimer's disease (SAD) remains a very active area of research,making it one of the most prolifically published areas in medicine and biology. Numerous putative candidate genes have been proposed. However, with the exception of apolipoprotein E (APOE), the only confirmed genetic risk factor for SAD, all the other data appear to be not consistent. Nevertheless, the genetic risk for SAD attributable to the APOE gene in the general population is 20-0%, providing a strong evidence for the existence of additional genetic risk factors. The first part of the present article was dedicated to non-APOE genetics of SAD, reviewing chromosomes-by-chromosomes the available data concerning the major candidate genes. The second part of this article focused on some recently discovered aspects of the APOE polymorphism and their implications for SAD. An attempt to identify the future directions for non-APOE genetic research in SAD was also discussed.

Evaluation of transforming growth factor and vascular endothelial growth factor polymorphisms in Taiwan Chinese patients with pterygium

PURPOSE

Pterygium is an invasive and highly vascularized growth, thought to arise from activated and proliferating limbal epithelial stem cells. Epidemiologic studies have found the increase of active angiogenic and epithelial growth factors in pterygia, and implicated that these molecules could be involved directly or indirectly in the pathogenesis of pterygia as causative factors. The aim of this study was to investigate the association of polymorphisms of transforming growth factor (TGF) and vascular endothelial growth factor (VEGF) with pterygium.

METHODS

A total of 133 pterygium patients and 105 volunteers without pterygium were enrolled in this study. Polymerase chain reaction based restriction fragment length polymorphism analysis was used to resolve the TGF-Beta1-509 and VEGF-460 genotypes.

RESULTS

There was no significant difference in the allele frequency or genotype of TGF-Beta1-509 or VEGF-460 between total pterygium and the control group. No interaction between TGF-Beta1-509 and VEGF-460 was found either.

CONCLUSIONS

These results indicate that TGF-Beta1-509 and VEGF-460 polymorphisms were not highly associated with the pathology of pterygium. However, it may still be worthwhile to continue to search for angiogenic gene polymorphisms in order to predict the development of pterygium.

Serum levels and genetic variation of TGF-beta1 are not associated with Alzheimer's disease

OBJECTIVE

As transforming growth factor-beta1 (TGF-beta1) determines important neurotrophic and neuroprotective actions, we postulated serum TGF-beta1 levels could be low in Alzheimer's disease (AD), and TGF-beta1 genetic variation could be associated with AD risk through modulating serum TGF-beta1 levels.

METHODS

TGF-beta1 (-800) (rs 1800468), (-509) (rs 1800469) and (+869) (rs 1982073) polymorphisms were genotyped in 412 AD patients and 406 controls. We measured serum TGF-beta1 levels (by ELISA) in 63 AD patients and compared them with 77 age- and gender-matched non-demented controls.

RESULTS

Serum TGF-beta1 levels were not different in AD patients than in controls. Distribution of the allele and genotype frequencies of TGF-beta1 polymorphisms did not differ between AD patients and controls. There was no significant correlation between serum TGF-beta1 levels and TGF-beta1 polymorphisms.

CONCLUSION

Serum TGF-beta1 concentration is not a potential biomarker for AD, and TGF-beta1 genetic variants (-800, -509, and +869) are not risk factors for AD.

+10 T/C polymorphisms in the gene of transforming growth factor-beta1 are associated with neurodegeneration and its clinical evolution

Transforming growth factor-beta1 (TGF-beta1) acts as an immunosuppressant by inhibiting the expression of several pro-inflammatory cytokines. Its gene contains single nucleotide polymorphisms (SNPs) at codon +10 (T-->C) and +25 (G-->C) that appear to influence the level of expression of TGF-beta1. We investigated these SNPs in 198 healthy controls (HC), 193 patients with Alzheimer's disease (AD) and 48 patients with mild cognitive impairment (MCI). Among the latter, after a 4-year follow-up, 21 were diagnosed as AD (MCI-->AD) while 18 did not progress (stable MCI). We observed that both the +10 C allele and the CC genotype were over-represented in AD when compared to HC. These variants significantly raised the risk of disease independently of the status of apolipoprotein E4. The CC genotype was also over-expressed in MCI, especially in MCI-->AD. These results suggest that TGF-beta1 may be one of the early markers involved in the inflammatory mechanisms underlying the pathogenesis of AD.

Analysis of common transforming growth factor beta-1 gene polymorphisms in gastric and duodenal ulcer disease: pilot study

BACKGROUND AND AIM

Transforming growth factor-beta1 (TGF-beta1) has been shown to be an important cytokine that plays a role in cell proliferation, differentiation, tissue injury repair and ulcer healing. The purpose of this pilot study was to investigate if common polymorphisms Leu10Pro, Arg25Pro and C-509T within the TGF-beta1 gene are associated with susceptibility to gastric and duodenal ulcer disease in Russians.

METHOD

Blood samples from 377 unrelated patients with gastric and duodenal ulcer disease and 226 sex- and age-matched healthy controls were used to determine TGF-beta1 gene polymorphisms by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

Leu10Pro substitution in the signal peptide of TGF-beta1 has been found to be associated with susceptibility to gastric ulcer (odds ratio [OR] 1.76, 95% confidence interval [CI] 1.12-2.77). A genotype combination of 10Leu/Leu x 25Arg/Arg x -509C/C was also associated with susceptibility to gastric ulcer disease (OR 1.81, P = 0.01). In addition, the frequency of a combination of genotypes 10Pro/Pro x 25Arg/Pro x -509C/T was statistically lower in patients with duodenal ulcer than in controls (OR 0.42, P = 0.05). A significant difference (P = 0.04) in the distribution of rare haplotypes of the TGF-beta1 gene between patients with duodenal ulcer and healthy controls has been found. Polymorphism Leu10Pro was in positive linkage disequilibrium with C-509T polymorphism (coefficient D = 0.191; P < 0.0001).

CONCLUSIONS

These findings indicate that the Leu10Pro and C-509T polymorphisms may be involved in the modulation of expression of the TGF-beta1 gene, and therefore a predisposition to peptic ulcer disease could be linked to particular alleles of this gene. In particular, a possible role of TGF-beta1 in the pathogenesis of gastric ulcer disease is discussed.

Polymorphisms in the interleukin 6 and transforming growth factor beta1 gene and risk of dementia. The Rotterdam Study

Inflammatory mechanisms are involved in the pathogenesis of dementia. Inflammatory cytokines, including interleukin-6 (IL-6) and transforming growth factor beta1 (TGFbeta1), have been found in association with Alzheimer pathology and there is evidence for direct involvement of these cytokines in formation of amyloid plaques. Polymorphisms in genes encoding for IL-6 and TGFbeta1 are associated with plasma levels of IL-6 and TGFbeta1. Studies examining the association between polymorphisms in these genes and dementia yielded conflicting results. The purpose of this study was to examine the association between genetic variance in IL-6 and TGFbeta1 and risk of dementia. We examined this association in the Rotterdam Study, a prospective population-based cohort study in the elderly. Polymorphisms in the IL-6 (-174G>C) and TGFbeta1 gene (-800G>A, -509C>T, +10T>C, +25G>C and 263C>T) were genotyped and haplotypes of the TGFbeta1 gene were constructed. In a random subset IL-6 plasma levels were measured. During follow-up (mean 9.2 years), 743 dementia cases were identified. We estimated the association between individual polymorphisms and haplotypes with dementia with Cox' proportional hazard models. No association was found between the -174G>C polymorphism in the IL-6 gene and risk of dementia. No association was found between polymorphisms and constructed haplotypes in the TGFbeta1 gene and risk of dementia or Alzheimer's disease. No association was found between IL-6 genotype and IL-6 plasma levels in the random subset. Associations did not differ across APOE genotypes. Our findings do not suggest involvement of genetic variance in IL-6 and TGFbeta1 in the development of dementia.

Allelic diversity in the TGFB1 regulatory region: characterization of novel functional single nucleotide polymorphisms

Altered TGF-beta1 expression due to polymorphisms affects a wide variety of normal cellular and disease processes such as T cell activation and proliferation, tumor progression, and asthma. In this study, a comprehensive examination of function and diversity was undertaken for the TGFB1 promoter region and exon 1 (-2,665 to +423). The known TGF-beta1 promoter was extended to encompass 463 bases by the identification of a strong enhancer activity for a distal segment (-2,665 to -2,204). Ten novel polymorphisms and 14 novel alleles were identified. Most single nucleotide polymorphisms (SNPs) appear to be randomly associated except c.-768_-769insC and c.+74G > C and a set of five novel polymorphisms present in a single allele in persons of African descent. The TGFB1 alleles clustered into three phylogenetic groups based on the common functional SNPs c.-1347C > T (commonly known as -509C-T) and c.+29T > C (commonly known as +869T-C) suggesting three phenotypic groups. Two SNPs unique to African-Americans affect the TGFB1 regulatory region. The c.-1287G > A SNP in the promoter alters the binding affinity of two unidentified transcription factor complexes which translates into a significant difference in reporter gene expression and the c.-387C > T SNP in the 5' UTR alters the binding of Stimulating protein 1 and 3. Thus, TGFB1 possesses a highly polymorphic, extensive regulatory region that likely impacts the pathogenesis of numerous TGF-beta1 related diseases.

Polymorphism for transforming growth factor beta 1-509 (TGF-B1-509): association with endometriosis

Transforming growth factor beta (TGF-B) family members are multi-functional cytokines that play a key role in cellular growth, proliferation, and differentiation. The aim of the study was to investigate whether the TGF-B1-509 gene polymorphism could be used as a marker of susceptibility in endometriosis. Women were divided into two groups: endometriosis (n = 150) and non-endometriosis (n = 159). Polymorphisms for TGF-B 1-509 genes were amplified by polymerase chain reaction and detected after restriction enzyme digestion. Genotypes and allelic frequencies in both groups were compared. Genotype proportions and allele frequencies of TGF-B1 gene polymorphisms differed significantly in both groups. Proportions of C homozygote, heterozygote, and T homozygote for TGF-B1 gene polymorphisms were 9.3/61.3/29.4% in the endometriosis group and 41.3158.510% in the non-endometriosis group. Alleles C and T for TGF-B1 gene polymorphism were 40/60% (endometriosis) and 70.8/29.2% (non-endometriosis). Association of endometriosis with TGF-B 1-509 gene polymorphism exists. T homozygote and T allele for TGF-B1 are associated with higher susceptibility to endometriosis.

Association studies of transforming growth factor-beta 1 and Alzheimer's disease

Substantial laboratory evidence suggests Transforming Growth Factor-beta1 (TGFB1) is linked to Alzheimer's Disease (AD) pathology. The purpose of the study was to estimate the genetic association of TGFB1 with AD while controlling for apolipoprotein E4 allele (APOE4) status, the only well-established genetic risk factor for AD. Two study populations were genotyped for the TGFB1-509 and +869 single nucleotide polymorphisms (SNPs) that have been associated with TGFB1 levels. Constituting these populations were 203 families from the NIMH AD Genetic Initiative with at least two affected siblings and a normal sibling, and a population of 126 African-American (AA) AD cases versus 93 age matched controls. Results from family-based analyses showed a significant association between the TGFB1 -509 SNP and AD for the entire set of 203 families (P = 0.007), and a subset of these families without a homozygous APOE4 family member (P = 0.026). Results from family-based analyses on the TGFB1 +869 SNP were not significant in the 203 families. While associations for the main effects of the TGFB1 +869 and -509 SNP with AD in the AA case-control study were also not significant, results did indicate that TGFB1 may function as an effect modifier of APOE4 risk. Specifically, the odds of AD associated with having at least one APOE4 allele increased in an additive fashion with one or two copies of the higher producer allele when stratified by TGFB1 -509 genotype and by TGFB1 +869 genotype. Results support a role for TGFB1 in AD pathogenesis.

Influence of polymorphisms in the genes for cytokines and glutathione S-transferase omega on sporadic Alzheimer's disease

We studied promoter region polymorphisms in the interleukin (IL)-1alpha, IL-1beta, IL-6, IL-10, tumor necrosis factor, and transforming growth factor (TGF)-beta1 genes in Japanese patients with Alzheimer's disease (AD) (n = 172) and normal controls (n = 163). We also examined an association of a polymorphism located in the glutathione S-transferase omega 1 (GSTO-1) gene region with AD patients. None of these genotypes or allele frequencies showed a significant difference between AD patients and controls. We also failed to detect any difference in the disease onset between each genotype of the seven polymorphisms. Although AD patients carrying high producer alleles of TGF-beta1 and IL-1beta or TGF-beta1 and IL-6 showed a tendency for an early onset of the disease, neither of these combined effects reached a significant level after multiple comparisons. Our findings suggest that genetic polymorphisms in the cytokines and GSTO do not play a major role in Japanese AD patients.

Analysis of the transforming growth factor-beta1 (TGF-beta1) codon 25 gene polymorphism by LightCycler-analysis in patients with chronic hepatitis C infection

The polymorphism at position 25 of the gene encoding transforming growth factor-beta1 (TGF-beta1), which changes the amino acid sequence of the signal peptide sequence (arginine to proline), is causing a variation in TGF-beta1 production. The homozygous genotype (Arg25Arg) is associated with higher TGF-beta1 production than the heterozygous (Arg25Pro) genotype. Therefore, the possible involvement of this genetic variation in the TGF-beta1 gene for induction and progression of various diseases is under close investigation. At present, several labor-intensive established assays ranging from amplification refractory mutation system (ARMS)-PCR methodologies, sequence specific oligonucleotide probing (SSOP), restriction fragment length polymorphism (RFLP) analysis, 5' nuclease assays, and specialized fingerprinting protocols are applied to analyze the polymorphism in question. We developed a novel approach for analyzing this polymorphism in a LightCycler system and determined the allele frequency distributions between patients with different degrees of hepatic fibrosis induced by chronic hepatitis C virus infection. In patients with severe hepatic fibrosis (METAVIR-score 3-4), the Pro25 allele was twice as frequent compared to patients with mild fibrosis (METAVIR-score 0-2). However, we found no association of necroinflammatory activity and genotype distribution. This suggests that the stage of hepatic fibrosis, rather than the grade (inflammation), is influenced by the presence of proline at codon 25 in patients with chronic hepatitis C.

Mutations in presenilin 1, presenilin 2 and amyloid precursor protein genes in patients with early-onset Alzheimer's disease in Poland

Mutations in three causative genes have been identified in patients with an autosomal-dominant form of early-onset Alzheimer's disease (EOAD). To determine the spectrum of mutations in a group consisting of 40 Polish patients with clinically diagnosed familial EOAD and 1 patient with mild cognitive impairment (MCI) and family history of AD, we performed a screening for mutations in the presenilin 1 (PSEN1), presenilin 2 (PSEN2) and amyloid precursor protein (APP) genes. Four previously recognized pathogenic mutations in PSEN1 gene (H163R, M139V) and APP gene (T714A, V715A), and three novel putative mutations in PSEN1 gene (P117R and I213F) and PSEN2 gene (Q228L) were identified. The 34 patients with no mutations detected were older than the patients with mutations. A frequency of APOE4 allele was higher in this group. Frequency of mutations is relatively low (17%), possibly due to used operational definition of a patient with familial EOAD (a patient having at least one relative with early-onset dementia). It could be concluded that screening for mutations in the three genes could be included in a diagnostic program directed at patients with a positive family history or age of onset before 55 years.

Promoter haplotypes of interleukin-10 gene and sporadic Alzheimer's disease

Clinical and immunopathological evidence support a potential role of the pro- and anti-inflammatory cytokine network in neurodegeneration of Alzheimer's disease (AD). Moreover, association studies suggest a possible involvement of cytokine-related genes in the susceptibility to sporadic AD. Since conflicting results are associated with the pro-inflammatory pathway, we investigated a putative effect of the anti-inflammatory counterpart focusing on the interleukin-10 (IL-10) gene. The 5' flanking region contains numerous polymorphisms; in particular, three single nucleotide polymorphisms (-1082 G/A, -819 T/C, -592 C/A) are in linkage disequilibrium resulting in three haplotypes GCC, ACC and ATA. We analyzed the IL-10 haplotype distributions in 215 Italian sporadic AD patients and 153 controls in an association case-control study. Haplotype frequencies did not reveal differences between the two samples, however the genotype GCC/ACC was more represented in AD patients (OR 1.91, 95% CI: 1.18-3.07). This putative risk factor could be independent of the presence of the ApoE epsilon 4 allele. Our results provide new insights on a possible involvement of the IL-10 gene in susceptibility to sporadic AD even though further functional and genetic investigations are necessary to clarify its role in AD.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.