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Alzheimer’s Disease Susceptibility Loci: Evidence for Natural Selection and Altered Gene Expression
Poster Presentations P1 levels can be measured in the cerebrospinal fluid (CSF) and plasma. Previous studies have failed to detect an association between APOE genotype and CSF levels of APOE. In this project, we tested whether APOE genotype or other variants in the APOE-TOMM40 region are associated with either CSF or plasma APOE levels. Methods: APOE protein levels in the cerebrospinal fluid and plasma were quantified using the Luminex xMAP Multiplexing Technology in 349 samples. Expression studies were carried out using cDNA obtained from the parietal lobes of 82 AD cases and 39 cognitively normal individuals (CDR ¼ 0). The SNPs that determine APOE genotype and 20 other SNPs in the APOETOMM40 region were genotyped by TaqMan or KASpar technology. Results: In our dataset, CSF and plasma APOE levels are not significantly correlated (R2¼0.10;p ¼ 0.08), however APOE genotype is strongly associated with both CSF (R2¼0.14; p ¼ 2.4x1011) and plasma APOE levels (R2¼0.26; p ¼ 2.4x1024). No association was found with any other genotyped SNP in the APOE-TOMM40 region when APOE genotype was included as covariate in the model. No association between APOE genotype and APOE mRNA expression was found (R2¼0.05; p ¼ 0.28). Conclusions: We confirmed that APOE genotype is associated with plasma APOE protein levels and failed to observe evidence for any other variation in this region influencing plasma APOE. In contrast to previous results we also observed a strong association between APOE genotype and APOE protein levels in CSF. This may be due to sample size or differences in the ELISA used to measure APOE levels. We did not find an association with APOE gene expression levels. The differences in APOE protein levels in CSF may be due to differences in APOE clearance or degradation resulting from differences in affinity of the APOE isoforms for its receptor.
P1-225
SYNERGISTIC EFFECTS OF GENETICS AND SPORTS CONCUSSIONS IN AGING
Louis De Beaumont1, Sebastien Tremblay2, Judes Poirier3, 1Douglas Mental Health Institute, Verdun, Quebec, Canada; 2Universite de Montreal, Montreal, Quebec, Canada; 3McGill University, Verdun, Quebec, Canada. Background: Media exposure to career ending concussive injuries among high-profile professional athletes as well as recent associations made between a history of multiple concussions in former professional athletes and the development of both dementia pugilistica and Alzheimer’s disease significantly helped making this epidemic a major public health concern. This study tested whether concussions and the APOE4 genotype synergistically affected measures of hippocampal volume, cortical thickness and magnetic resonance spectroscopy in relation with performance scores on neuropsychological tests highly sensitive to MCI. Methods: Fifteen former athletes who sustained their last sports concussion more than three decades ago were compared to fifteen former athletes with no history of traumatic brain injury. Participants underwent quantitative neuroimaging (optimized voxel-based morphometry, hippocampal volume, cortical thickness), proton magnetic resonance spectroscopy (medial temporal lobes, prefrontal cortices, left primary motor cortex), neuropsychological testing (episodic memory, verbal fluency, implicit motor learning), and were genotyped for APOE polymorphisms. Results: Relative to controls, former athletes with concussions exhibited: (i) Episodic memory, verbal fluency and implicit motor learning decline; (ii) various neurometabolic anomalies in all three regions of interest; (iii) abnormal enlargement of the lateral ventricles; (iv) cortical thinning in regions more vulnerable to the aging process; (v) and hippocampal atrophy resulting from a synergistic effect with APOE-e4. These neuroanatomical findings were associated with cognitive decline in concussed participants. Conclusions: This original study associates neurobiological underpinnings to long term detrimental effects of sports concussion on cognition. More importantly, former athletes with remote concussions exhibit a pattern of cognitive decline and neurobiological anomalies strikingly similar to that of patients diagnosed with mild cognitive impairment (MCI), which refers to a transitional phase between normal aging and Alzheimer’s disease.
P1-226
S183 ALZHEIMER’S DISEASE SUSCEPTIBILITY LOCI: EVIDENCE FOR NATURAL SELECTION AND ALTERED GENE EXPRESSION
Towfique Raj1, Joshua Shulman1, Lori Chibnik2, Brendan Keenan1, Barbara Stranger1, Denis Evans2, David Bennett3, Philip De Jager1, 1 Brigham and Women’s Hospital, Boston, Massachusetts, United States; 2 Harvard Medical School, Boston, Massachusetts, United States; 3Rush Univ, Chicago, Illinois, United States. Background: Genome-wide association (GWA) studies have identified several Alzheimer’s disease (AD) susceptibility loci. To dissect the functional consequences of the associated genetic variants, we explored large-scale data sets interrogating the human genome for evidence of positive natural selection and of effects on gene expression in each associated locus. Methods: To assess for evidence of natural selection, we used the integrated Haplotype Score (iHS) method and HapMap phaseII data. For the gene expression studies, we used (1) a publicly available dataset generated from purified monocytes of 1,490 healthy individuals and (2) data generated from the peripheral blood mononuclear cells (PBMC) of 228 subjects with demyelinating disease. A quantitative trait analysis using an additive model was implemented (PLINK toolkit). Validated and strongly suggested AD susceptibility loci were considered. Results: We find that the validated CR1 and PICALM as well as the suggested loci GAB2 and MTHFD1L harbor haplotypes with evidence of recent selective sweep. For example, the haplotype carrying the AD risk allele rs2373115*G in GAB2 shows strong evidence of positive selection after correction for genome-wide testing (p < 0.003). Further, using phylogeny-based methods, we report that the CR1 and CLU loci may have experienced adaptive evolution along the human lineage. These results, along with prior reports describing selection in the APOE locus, provides compelling anecdotal evidence of natural selection in AD susceptibility loci. Given that several loci may contain immune system genes, we speculate that the selective pressure underlying adaptive evolution of these genes may have been due to resistance to pathogens. To support the hypothesis that these alleles may influence the function of immune cells, we analyzed gene expression data from monocytes and PBMC and identified 3 cis-regulatory effects among the 24 tested loci, including the rs3826656 variant (Bertram et al. AJHG 2008) which is associated with the expression of CD33 in monocytes (p ¼ 4.07 x 1017) and in PBMC (p ¼ 3.94 x 104). Conclusions: Our data suggest that several different genes implicated in AD susceptibility may have worked together in another context, perhaps in the immune system, to enhance survival over the course of evolution. P1-227
DO AFRICAN AMERICANS HAVE THE SAME TOMM40 DISTRIBUTION AS CAUCASIANS? PRELIMINARY RESULTS FROM WISCONSIN REGISTRY FOR ALZHEIMER’S PREVENTION (WRAP)
Dorothy Edwards1, Rebecca Koscik1, Erin Jonatis1, Asenath LaRue1, Bruce Hermann1, Gina Green-Harris2, Soryal Soryal3, Mark Sager1, 1 University of Wisconsin School of Medicine, Madison, Wisconsin, United States; 2Medical College of Wisconsin, Milwaukee, Wisconsin, United States; 3Aurora Sinai Hospital, Milwaukee, Wisconsin, United States. Background: African Americans are at greater risk for late onset Alzheimer’s disease (LOAD) than other racial groups. Genetic risk factors for (LOAD) include presence of one or more APOEe4 alleles and family history of LOAD. Length of the poly-T sequence, rs10524523, within intron 6 of the TOMM40 gene has been linked to age of onset in a non-Hispanic Caucasian LOAD sample. Using a healthy middleaged sample of African Americans and non-Hispanic Caucasians, we examined the relationships among race, TOMM40, family history of LOAD (FH), and APOE e4status. Methods: Non-Hispanic Caucasian (n ¼ 1242) and African American (n ¼ 77) participants in the Wisconsin Registry for Alzheimer’s Prevention (WRAP) with TOMM40 data were eligible. Using Lutz et al.’s (2010) cutoffs, we categorized allele lengths as short (S;
P1-225
SYNERGISTIC EFFECTS OF GENETICS AND SPORTS CONCUSSIONS IN AGING
Louis De Beaumont1, Sebastien Tremblay2, Judes Poirier3, 1Douglas Mental Health Institute, Verdun, Quebec, Canada; 2Universite de Montreal, Montreal, Quebec, Canada; 3McGill University, Verdun, Quebec, Canada. Background: Media exposure to career ending concussive injuries among high-profile professional athletes as well as recent associations made between a history of multiple concussions in former professional athletes and the development of both dementia pugilistica and Alzheimer’s disease significantly helped making this epidemic a major public health concern. This study tested whether concussions and the APOE4 genotype synergistically affected measures of hippocampal volume, cortical thickness and magnetic resonance spectroscopy in relation with performance scores on neuropsychological tests highly sensitive to MCI. Methods: Fifteen former athletes who sustained their last sports concussion more than three decades ago were compared to fifteen former athletes with no history of traumatic brain injury. Participants underwent quantitative neuroimaging (optimized voxel-based morphometry, hippocampal volume, cortical thickness), proton magnetic resonance spectroscopy (medial temporal lobes, prefrontal cortices, left primary motor cortex), neuropsychological testing (episodic memory, verbal fluency, implicit motor learning), and were genotyped for APOE polymorphisms. Results: Relative to controls, former athletes with concussions exhibited: (i) Episodic memory, verbal fluency and implicit motor learning decline; (ii) various neurometabolic anomalies in all three regions of interest; (iii) abnormal enlargement of the lateral ventricles; (iv) cortical thinning in regions more vulnerable to the aging process; (v) and hippocampal atrophy resulting from a synergistic effect with APOE-e4. These neuroanatomical findings were associated with cognitive decline in concussed participants. Conclusions: This original study associates neurobiological underpinnings to long term detrimental effects of sports concussion on cognition. More importantly, former athletes with remote concussions exhibit a pattern of cognitive decline and neurobiological anomalies strikingly similar to that of patients diagnosed with mild cognitive impairment (MCI), which refers to a transitional phase between normal aging and Alzheimer’s disease.
P1-226
S183 ALZHEIMER’S DISEASE SUSCEPTIBILITY LOCI: EVIDENCE FOR NATURAL SELECTION AND ALTERED GENE EXPRESSION
Towfique Raj1, Joshua Shulman1, Lori Chibnik2, Brendan Keenan1, Barbara Stranger1, Denis Evans2, David Bennett3, Philip De Jager1, 1 Brigham and Women’s Hospital, Boston, Massachusetts, United States; 2 Harvard Medical School, Boston, Massachusetts, United States; 3Rush Univ, Chicago, Illinois, United States. Background: Genome-wide association (GWA) studies have identified several Alzheimer’s disease (AD) susceptibility loci. To dissect the functional consequences of the associated genetic variants, we explored large-scale data sets interrogating the human genome for evidence of positive natural selection and of effects on gene expression in each associated locus. Methods: To assess for evidence of natural selection, we used the integrated Haplotype Score (iHS) method and HapMap phaseII data. For the gene expression studies, we used (1) a publicly available dataset generated from purified monocytes of 1,490 healthy individuals and (2) data generated from the peripheral blood mononuclear cells (PBMC) of 228 subjects with demyelinating disease. A quantitative trait analysis using an additive model was implemented (PLINK toolkit). Validated and strongly suggested AD susceptibility loci were considered. Results: We find that the validated CR1 and PICALM as well as the suggested loci GAB2 and MTHFD1L harbor haplotypes with evidence of recent selective sweep. For example, the haplotype carrying the AD risk allele rs2373115*G in GAB2 shows strong evidence of positive selection after correction for genome-wide testing (p < 0.003). Further, using phylogeny-based methods, we report that the CR1 and CLU loci may have experienced adaptive evolution along the human lineage. These results, along with prior reports describing selection in the APOE locus, provides compelling anecdotal evidence of natural selection in AD susceptibility loci. Given that several loci may contain immune system genes, we speculate that the selective pressure underlying adaptive evolution of these genes may have been due to resistance to pathogens. To support the hypothesis that these alleles may influence the function of immune cells, we analyzed gene expression data from monocytes and PBMC and identified 3 cis-regulatory effects among the 24 tested loci, including the rs3826656 variant (Bertram et al. AJHG 2008) which is associated with the expression of CD33 in monocytes (p ¼ 4.07 x 1017) and in PBMC (p ¼ 3.94 x 104). Conclusions: Our data suggest that several different genes implicated in AD susceptibility may have worked together in another context, perhaps in the immune system, to enhance survival over the course of evolution. P1-227
DO AFRICAN AMERICANS HAVE THE SAME TOMM40 DISTRIBUTION AS CAUCASIANS? PRELIMINARY RESULTS FROM WISCONSIN REGISTRY FOR ALZHEIMER’S PREVENTION (WRAP)
Dorothy Edwards1, Rebecca Koscik1, Erin Jonatis1, Asenath LaRue1, Bruce Hermann1, Gina Green-Harris2, Soryal Soryal3, Mark Sager1, 1 University of Wisconsin School of Medicine, Madison, Wisconsin, United States; 2Medical College of Wisconsin, Milwaukee, Wisconsin, United States; 3Aurora Sinai Hospital, Milwaukee, Wisconsin, United States. Background: African Americans are at greater risk for late onset Alzheimer’s disease (LOAD) than other racial groups. Genetic risk factors for (LOAD) include presence of one or more APOEe4 alleles and family history of LOAD. Length of the poly-T sequence, rs10524523, within intron 6 of the TOMM40 gene has been linked to age of onset in a non-Hispanic Caucasian LOAD sample. Using a healthy middleaged sample of African Americans and non-Hispanic Caucasians, we examined the relationships among race, TOMM40, family history of LOAD (FH), and APOE e4status. Methods: Non-Hispanic Caucasian (n ¼ 1242) and African American (n ¼ 77) participants in the Wisconsin Registry for Alzheimer’s Prevention (WRAP) with TOMM40 data were eligible. Using Lutz et al.’s (2010) cutoffs, we categorized allele lengths as short (S;