S.E. Poduslo

Genetic variants in brain-derived neurotrophic factor associated with Alzheimer’s disease

Background: Alzheimer’s disease is complex, with variants in multiple genes contributing to interactions increasing risk for the disease. Brain-derived neurotrophic factor (BDNF) promotes neuronal survival and modulates hippocampal-dependent memory. Methods: We examined 11 SNPs that spanned the gene on chromosome 11p14 in 220 Alzheimer’s patients and 128 control spouses. Results: Not all of the SNPs were informative, due to minor allele frequencies of <2%. Neither C270T nor two SNPs that reside proximal to exon V had significant association with the disease. However, we did find that the heterozygous form of the rs6265 SNP (Val66Met), as well as the diplotype of three SNPs (rs6265, rs11030104, rs2049045; H1-GTC/H2-ACG) all were highly significant in APOE 4 non-carriers (OR = 2.734; p = 0.0096). Conclusion: The combination of the diplotypes for three SNPs exhibited significant p values for Alzheimer’s APOE 4 non-carriers. The two SNPs (rs11030104 and rs2049045) are found between exons VI and VII, while the Val66Met polymorphism is located in the coding exon VIII; the total distance for the three SNPs is 14308 bp. Whether the SNPs are involved with alternative splicing of the VII/VIII transcript is of considerable interest.

CYP19 haplotypes increase risk for Alzheimer’s disease

Cytochrome P450 aromatase, an enzyme that catalyses the conversion of androgens to oestrogen, is expressed at high levels in the gonads and in the brain. Aromatase activity is increased in the nucleus basalis of Meynert during aging and in Alzheimer’s disease (AD), making the gene (CYP19), at 15q21.1, a potential candidate risk factor.We examined 18 single nucleotide polymorphisms spanning the 5′-untranslated region and the entire coding region of CYP19 in 227 patients with AD and 131 control spouses.We found that the gene region could be divided into two haplotype blocks; a haplotype in block 1 and a haplotype in block 2 increased the risk of developing the disease by twofold in APOE 4 carriers. The implication of two haplotypes conferring increased risk for AD warrants further investigation of the regulation of aromatase activity in brain.

Cystatin C as a risk factor for Alzheimer disease.

Cystatin C, a protease inhibitor with widespread distribution, is upregulated in response to injury. Levels are elevated in the brains of patients with Alzheimer disease (AD). We compared frequencies for the CST 3 exon 1 polymorphism in patients with AD and controls. A proportional odds model indicated that the CST 3 A and APOE4 combination carried a high risk: a 14-fold elevation for men and 16-fold for women. These risks apply to risk at ages older than 64 years and to a shift in onset to ages younger than 65 years.

Functional interaction between APOE4 and LDL receptor isoforms in Alzheimer’s disease

Background: Multiple genes have been provisionally associated with Alzheimer’s disease, including the coding polymorphisms in exons 8 and 13 in the low density lipoprotein receptor gene (LDLR), situated on chromosome 19p13.2. Methods: The sample groups consisted of 180 AD patients and 141 control spouses. We carried out genotyping of LDLR8 and LDLR13. Results: The LDLR8 GG genotype was common, found in 84% of the unaffected control subjects and 91% of the AD patients in our study. There was a ninefold elevation in risk associated with GG:CC versus A– and T– among APOE4+ subjects when compared with APOE4− subjects (odds ratio 9.3; 95% confidence interval 1.8 to 48.2). With the additional information on LDLR polymorphism, we defined an overall 12 fold elevation in risk for APOE4 in combination with LDLR GG:CC (11.9; 2.8 to 50.0; Fisher’s exact test, p = 0.0002; standard power 0.999), compared with other subjects lacking all three of these polymorphisms. Conclusion: These results imply a functional interaction between ApoE and LDL receptor proteins that determines risk for Alzheimer’s disease.

Apolipoprotein gene E4 allele promoter polymorphisms as risk factors for Alzheimer's disease.

Alzheimers disease is a complex neurodegenerative disorder, characterized by progressive cognitive decline and distinct neuropathology. The apolipoprotein gene E4 allele (APOE 4) is a major risk factor for the disease. Promoter polymorphisms at −491 and −427 may also contribute to the risk. We examined the two polymorphisms in 178 Alzheimers patients and 141 controls. The −491AA genotype was overrepresented among the patients (68 versus 54%, P=0.01). However, in patients who were APOE4 carriers, the −491AA genotype more than doubled the risk [odds ratio (OR)=2.5; 95% confidence interval (CI)=1.2–5.4], especially in combination with −427TT [odds ratio (OR)=3.3; 95% confidence interval (CI)=1.5–7.7]. Moreover, the −491A/−427T/APOE4/APOC1A haplotype was threefold higher for patients. These results contribute to the evidence that regulation of APOE4 expression modulates risk for Alzheimers disease.

Cluster analysis of risk factor genetic polymorphisms in Alzheimer's disease.

Multiple genetic variants may contribute to the risk of developing Alzheimer’s disease. We have analyzed polymorphisms in 9 genes to determine whether particular combinations would contribute to this risk. The genes were APOE, LDLr, CST3, CTSD, TNF, BACE1, MAPT, STH, eNOS, and TFCP2. Three risk groups for the disease were identified. Risk group I was younger, was heterozygous for the CST3 (GA), CTSD2936 (AG), TNF -308 (AG) genetic variants. Risk group II was older, was homozygous for the −427 APOE promoter polymorphism (TT), and heterozygous for the MAPT deletion and for the STH variant (QR). Group III had both the youngest and oldest subjects, were heterozygous for the −863 (AC) and −1031 (CT) TNF promoter polymorphisms. All three groups carried the APOE 4 allele and were heterozygous for both BACE1 polymorphisms. The control groups were carriers of the APOE 3 allele and were homozygous for the BACE1 genetic variants.

APOE genotypes in African American female multiple sclerosis patients

Multiple sclerosis (MS) is a chronic inflammatory CNS disorder, resulting in progressive neurological dysfunction. The disease has a higher incidence in Caucasian Americans (CA) than African Americans (AA); however, the latter may have a more aggressive disease course. We used cluster analysis to determine whether there is a difference in disease progression between the races and whether the APOE AND APOC1 genotypes influence the disease progression. AA female patients were younger and had a higher progression index and MS severity score than CA female MS patients. AA females who were APOE 4/4, 2/4, or 2/3 and APOC1 AA had a younger age-of-onset, had primarily a relapsing remitting disease course, with a higher progression index and MS severity score, as assessed by cluster analysis. Cluster analysis also indicated that CA female patients were of two groups. One group was younger, had the APOE 3/3 genotype with relapsing remitting less severe disease. The second CA group was older, had the APOE 3/4 or 2/3 genotypes with more of the secondary progressive more severe disease phenotype. Thus, the AA MS female patients who were APOE 4 carriers had an earlier age-of-onset and more severe disease course than CA MS female patients.

The frequency of the TRPC4AP haplotype in Alzheimer's patients.

A haplotype in the gene for transient receptor potential cation channel, subfamily C, member 4 associated protein (TRPC4AP), has been identified in two extended pedigrees with late-onset Alzheimers disease. Nine of the SNPs in the haplotype were analyzed in our unrelated Alzheimers patients and controls. The H1 haplotype was found in 36% of the patients (199 patients) and in 26% of the controls (85 controls) (P=0.0282; OR=1.56; 95%CI=1.05-2.32). The latent classification method of analysis showed that the H1 haplotype was characteristic of Alzheimers patients, with ages-of-onset between 66 and 80 years. When clinical phenotypes were analyzed, there was a suggestion that the patients with this haplotype may have more behavioral changes and hallucinations. Moreover, both the latent classification analysis and logistic regression analysis indicated that there was no association of the haplotype with either APOE status or gender. The gene is part of a superfamily of cation channels that are involved with calcium entry into cells.

P1-301: Genetic studies of a late-onset Alzheimer’s extended pedigree

aging. This observation is consistent with the idea that the gradual downregulation of NEP expression, resulting in a corresponding elevation in the steady-state levels of A , over a decade or more, may cause A accumulation that triggers the AD pathological cascade. Additionally, higher mRNA levels of IDE and NEP were detected in the human cerebellum than in the frontal cortex, which may partly explain why cerebellum exhibits only minor plaque pathology. Conclusions: These data suggest that ageand region-specific changes in the proteolytic clearance of A make an important contribution to pathogenic mechanisms in AD.

P3-252: Genome screen of extended families with late-onset Alzheimer's disease versus successful aging

Paola Piscopo, Giuseppina Talarico, Ornella Spadoni, Lorenzo Malvezzi-Campeggi, Alessio Crestini, Marina Gasparini, Nicola Vanacore, Gian Luigi Lenzi, Maurizio Pocchiari, Annamaria Confaloni, Giuseppe Bruno, Dept of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy; Memory Clinic, Dept. Neurological Sciences, University of Rome “Sapienza”, Rome, Italy. Contact e-mail: paola.piscopo@iss.it