- Email: [email protected]
Cholesterol in amyloid plaques: Analysis by laser capture microdissection combined with mass spectrometry
P110
Oral O2-04: Disease Mechanisms: APOE
and apoE3 in the e3/4 mouse brains. ApoE4 represented 30-40 % of the total apoE. Moreover, the absolute amount of apoE3 per allele was similar between e3/3 and e3/4 mice, implying that the reduced levels of total apoE in e3/4 mice can be explained by the reduction in apoE4 levels. In culture medium from e3/4 human astrocytoma or e3/3, e4/4 and e3/4 primary astrocytes, apoE4 levels were consistently lower than apoE3. Secreted cholesterol levels were also lower from e4/4 astrocytes. Pulse-chase experiments showed an enhanced degradation and reduced half-life of newly synthesized apoE4 compared to apoE3. Taken together these data suggest that astrocytes preferentially degrade apoE4, leading to reduced apoE4 secretion and ultimately to reduced brain apoE levels. Next we examined the physiological relevance of these findings. Firstly, as apoE has been shown to enhance the degradation of Ab, we measured the endogenous levels of Ab in e4/4 and e3/3 mice. As previously reported for the human population, e4/4 mice had higher levels of Ab42 in their hippocampus and cortex. Next we examined the capacity of astrocytic e3/3 and e4/4 to promote neurite outgrowth. Interestingly, and unlike previous reports, we found that astrocytic lipoproteins prepared from e4/4 mice, was able to promote neurite outgrowth and increase synaptophysin expression, but with 10 fold less potency than particles from e3/3 mice. Conclusions: Taken together these data suggest that the low levels of astrocytic apoE/ cholesterol secreted by e4 carriers may directly contribute to the disease progression by reducing apoE’s capacity to promote synaptic repair and Ab clearance. O2-04-03
APOE GENOTYPE AND AMYLOID BETA EFFECTS ON COGNITION ARE MEDIATED BY CELL INJURY (TAU) AND DEATH (PROGRESSIVE ATROPHY)
Charles DeCarli, Owen Carmichael, Danielle Harvey, Evan Fletcher, Dan Mungas, University of California at Davis, Sacramento, CA, USA. Contact e-mail: [email protected] Background: The amyloid hypothesis suggests a primary role for Ab, although clinical symptoms are most closely associated with neurofibrillary formation and neuronal injury and loss. We hypothesized that CSF tau would therefore mediate the effect of CSF Ab on cognitive performance (Figure). Methods: 313 subjects from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) for whom baseline CSF, repeated MRI and repeated Cognitive measures were evaluated. Subjects included 70 AD, 152, MCI and 91 Cognitively normal individuals mean age 74.8 þ 7.0 years. Baseline brain and hippocampal volumes were calculated as well as yearly rates of both measures using a fluid flow deformation method to determine jacobian determinant expansion or contraction for each image voxel. Cognitive measures included 1-year change in delayed story recall and ADAS-Cog. Multiple regression analysis was used to systematically test the effects of CSF Ab, CSF Tau, baseline and change in brain volume
on change in cognition at 1 year. Results: Significant associations were found between the rate of change of cognitive measures and ApoE4 genotype, CSF Ab, CSF Tau, baseline and rate of whole brain atrophy adjusting for age, education and gender (see table). The impact of CSF Ab remained significantly associated with change in cognitive measures in a multiple regression model that included both CSF Ab and ApoE genotype (p <0.0001). CSF Tau was also significantly associated with change in delayed story recall (p¼0.0002) and ADAS-Cog (p<0.0001) when added to the model. In a model predicting change in ADAS-Cog which included baseline and change in whole brain volume as well as CSF Tau and Ab, CSF Tau (p<0.0002), baseline, longitudinal brain atrophy (p<0.0001), but not CSF Ab were significantly associated with change in ADAS-Cog. Conversely, in a model predicting change in delayed story recall, CSF Ab (p < 0.0001), CSF Tau (p¼0.013), baseline hippocampus (p < 0.0001), change in hippocampal (p ¼0.016) and brain volume (p<0.0011) were each significantly associated with rate of change in delayed story recall. Conclusions: CSF Ab has both direct and mediated effects on specific cognitive domains. Reductions in both CSF Ab and CSF tau, therefore, should be considered good markers of therapeutic efficacy in AD clinical trials.
O2-04-04
CHOLESTEROL IN AMYLOID PLAQUES: ANALYSIS BY LASER CAPTURE MICRODISSECTION COMBINED WITH MASS SPECTROMETRY
Maı¨ Panchal1, Jacqueline Loeper2, Claire Perruchini3, Adina Lazar3, Heidi Vitrac3, Denis Pompon2, Charles Duyckaerts3, 1Hoˆpital de la Salpeˆtrie`re, 75013 Paris, France; 2CNRS-CGM, Gif-sur-Yvette, France; 3Hoˆpital de la Salpeˆtrie`re, Paris, France. Contact e-mail: [email protected] Background: The presence of senile plaques (SP) in the brain is one of the pathological hallmarks of Alzheimer’s disease (AD). Extensive knowledge of the protein components of the SP has been acquired over the years but the lipids associated with amyloid beta-peptide (Ab) deposits remain unknown. Many evidences suggest that cholesterol contributes to the pathogenesis of AD. Two studies have reported that SP were enriched in cholesterol. We provided data suggesting that these results were obtained with poorly specific methods (Lebouvier et al. 2009). The presence of cholesterol in the senile plaque remains to be demonstrated. Methods: Experiments were performed on frozen brain sections (10 um-thick sections from samples of first temporal gyrus) from three sporadic Braak stage
Oral O2-04: Disease Mechanisms: APOE VI AD cases with numerous amyloid cortical plaques. Laser capture microdissection (LCM) of SPs and of Ab free neuropil was performed immediately after Ab immunohistochemistry with short incubation times. The quantity of Ab peptide in an identical volume of Ab-free neuropil and of senile plaque core was compared. After lipid extraction, the samples were analyzed by liquid chromatography combined with mass spectrometry (LC-MS), using cholesterol standards. Results: We demonstrated a statistically significant increase of cholesterol in SPs versus neuropil. These data combined with the known presence of ApoE, the cholesterol transporter, in the SPs suggest that cholesterol plays a role in the formation and/or progression of the plaques. Conclusions: LCM allowed us to isolate a pure preparation of amyloid core. This preparation was enriched in cholesterol when compared to plaque-free neuropil. This methodology can be extended to analyze other pathological structures in various neurodegenerative disorders.
O2-04-05
NOVEL MECHANISM WHERE APOE MIMETICS ACTIVATE PP2A ACTIVITY AND REDUCE ALZHEIMER’S PATHOLOGY IN THREE DIFFERENT TRANSGENIC MODELS
Michael P. Vitek1, Dale J. Christensen1, Donna Wilcock2, Jessica Oddo1, Nastaran Gharkholonarehe2, Nobutaka Ohkubo2, Kazuko Toku2, William E. Van Nostrand3, Fengqiao Li1, Carol A. Colton2, 1Cognosci, Research Triangle Park, NC, USA; 2Duke University Medical Center, Durham, NC, USA; 3Stony Brook University, Stony Brook, NY, USA. Contact e-mail: [email protected] Background: The second largest risk factor for AD is APOE genotype, where APOE4 is also associated with lower apoE levels, more severe brain pathology and inflammation. We reported that small peptides corresponding to the receptor-binding region of apoE could mimic the anti-inflammatory activity of the apoE holoprotein (Lynch et al. 2003). When given systemically after brain trauma and/or hemorrhage, these apoE-mimetics greatly improved behavioral outcomes and neuronal survival (Laskowitz et al. 2007, James et al. 2008). Methods: To understand this protective activity, we employed biotinylated-apoE-mimetics and affinity purified I2PP2A as a major binding protein in mouse and human brains. I2PP2A is a natural inhibitor of PP2A, the key protein phosphatase associated with dephosphorylation of many important proteins. Addition of apoE-mimetics significantly stimulates PP2A’s phosphatase activity resulting in dramatic inhibition of tumor necrosis factor alpha (TNFa) release following stimulation with lipopolysaccharide (LPS). Similarly, siRNA to I2PP2A also reduces phospho-protein and TNFa levels following LPS, and these reductions are not further increased with added apoE-mimetics. Results: Since PP2A can greatly reduce phospho-tau associated with neurofibrillary tangle-like structures (NFTs), we tested the ability of peripherally administered apoE-mimetics to reduce phospho-tau AT8-immunoreactive staining in the brains of transgenic mice. After nine months, JNPL3 (P301L tau) mice on a NOS2-/- background (Colton et al. unpublished), Tg2576 (APPsw) on a NOS2-/- background (Colton et al. 2006), and APP-SwDI on a NOS2-/- background (Wilcock et al. 2008) were treated with apoE-mimetics for three months and brain pathology was evaluated. In each case, an obvious reduction in AT8-labeled NFT-like structures was observed in the apoE-mimetic treated animals. Additionally, in APP-Sw/NOS2-/- and APP-SwDI/NOS2-/- mice treated with apoE-mimetics, there was also a clear reduction in Abeta-immunostained amyloid deposits. Since they also improve outcomes after brain hemorrhage, we are currently testing the effect of apoE-mimetics on Abeta-immunized APP-transgenics, which show increased incidence of microhemorrhage. Conclusions: In addition to replacing the lost function of lowered apoE levels, apoE-mimetics cross the blood brain barrier to bind I2PP2A and antagonize this inhibitor, resulting in activation of PP2A. Increased PP2A activity reduces phospho-tau levels and amyloid deposits in multiple Alzheimer’s transgenics suggesting the use of apoE-mimetics as therapeutics in AD.
O2-04-06
P111
GRB-ASSOCIATED BINDING PROTEIN 2 (GAB2) INTERACTS WITH APOE TO ALTER RISK OF LATE-ONSET ALZHEIMER’S DISEASE
Gary W. Beecham1, Adam C. Naj1, Guiqing Cai2, Yuji Kajiwara2, Vahram Haroutunian2, Ioanna Konidari1, Paul Gallins1, Patrice Whitehead1, John R. Gilbert1, Michael A. Slifer1, Harry Gwirstman3, Eden R. Martin1, Joseph Buxbaum2, Jonathan L. Haines4, Margaret A. Pericak-Vance1, 1University of Miami, Miller School of Medicine, Miami, FL, USA; 2Mount Sinai School of Medicine, Department of Psychiatry, New York, NY, USA; 3VA Hospital Medical Center, Department of Psychiatry, Nashville, TN, USA; 4Vanderbilt University, Center for Human Genetics Research, Nashville, TN, USA. Contact e-mail: [email protected] Background: Other than the apolipoprotein E (APOE) gene, there have been no consistently replicated genetic risk factors for late-onset Alzheimer disease (LOAD). Numerous candidate genes have been proposed but validation of genetic association signals has proven difficult. One such candidate gene is GRB-associated binding protein 2 (GAB2). GAB2, associated with LOAD in APOE-4 carriers in a published genome-wide association study (p-value ¼ 9 x 10-11), is over expressed in LOAD brain, and has been shown to influence Alzheimer’s neuropathology. Methods: To investigate the role of GAB2 in LOAD we examined 22 SNPs across the GAB2 gene in a large cohort of 876 LOAD cases and 804 cognitive controls. Cases and controls were gender and age matched, and affection status was confirmed through either 3MS or MMSE batteries. Genotypes were obtained from Illumina HumanHap beadchips and extensive quality-control measures were implemented, including correction for population substructure. Association was tested under an additive model and interaction with APOE was considered in the model. IMPUTE was used to infer genotypes at the rs2373115 SNP, the SNP with strong association in the previous association study. Results: We confirm the association of GAB2 with LOAD. Of the 22 SNPs genotyped, 19 showed significant interaction with APOE (p-values ¼ 0.04 to 0.004; odds ratio ¼ 1.5 to 1.9 for the interaction term). The additive effect of GAB2 was not significant, even after controlling for APOE genotype. The rs2373115 SNP was successfully imputed and also shows significant interaction with apoE genotypes (p-value¼0.015; OR¼1.63). The interaction appears to be largely driven by the APOE-4 positive controls; the e4 positive controls have an excess of the major GAB2 homozygote (p-value ¼ 0.0013), implying that the genotype mitigates the effect of the e4 allele. Conclusions: We have replicated the GAB2 interaction with APOE, showing statistical significance in a large cohort. This analysis confirms that GAB2 is an excellent candidate gene for late-onset Alzheimer disease, and highlights the need for further delineation of interaction effects in the search for genetic risk factors.
O2-04-07
MOST RAPID COGNITIVE DECLINE IN APOE4 NEGATIVE ALZHEIMER’S DISEASE WITH EARLY ONSET
Wiesje M. van der Flier, Annelies E. van der Vlies, Esther L. Koedam, Yolande A. L. Pijnenburg, Jos W. R. Twisk, Philip Scheltens, VU Medical Center, Amsterdam, Netherlands. Contact e-mail: [email protected] Background: We aimed to compare the rate of cognitive decline in patients with early and late onset Alzheimer’s Disease (AD) and to investigate the potentially modifying influence of APOE genotype. Methods: We included 99 patients with early onset AD (age 65 years) and 192 patients with late onset AD (age >65 years) who had at least 2 MMSE scores (range 2-14) obtained at least one year apart. Linear mixed models were performed to investigate the rate of cognitive decline dependent on age-at-onset and APOE genotype. Results: Mean (sd) age for patients with early onset was 57.7 (4.5) years, and 74.5 (5.1) for patients with late onset. Age-at-onset was not associated with baseline MMSE (b(SE)¼ 0.8 (0.5), p¼ 0.14). However, patients with early onset showed faster decline on the MMSE of (b(SE)) 2.4 (0.1) points/year, whereas those with late onset showed decline of 1.7 (0.1) points/year
Oral O2-04: Disease Mechanisms: APOE
and apoE3 in the e3/4 mouse brains. ApoE4 represented 30-40 % of the total apoE. Moreover, the absolute amount of apoE3 per allele was similar between e3/3 and e3/4 mice, implying that the reduced levels of total apoE in e3/4 mice can be explained by the reduction in apoE4 levels. In culture medium from e3/4 human astrocytoma or e3/3, e4/4 and e3/4 primary astrocytes, apoE4 levels were consistently lower than apoE3. Secreted cholesterol levels were also lower from e4/4 astrocytes. Pulse-chase experiments showed an enhanced degradation and reduced half-life of newly synthesized apoE4 compared to apoE3. Taken together these data suggest that astrocytes preferentially degrade apoE4, leading to reduced apoE4 secretion and ultimately to reduced brain apoE levels. Next we examined the physiological relevance of these findings. Firstly, as apoE has been shown to enhance the degradation of Ab, we measured the endogenous levels of Ab in e4/4 and e3/3 mice. As previously reported for the human population, e4/4 mice had higher levels of Ab42 in their hippocampus and cortex. Next we examined the capacity of astrocytic e3/3 and e4/4 to promote neurite outgrowth. Interestingly, and unlike previous reports, we found that astrocytic lipoproteins prepared from e4/4 mice, was able to promote neurite outgrowth and increase synaptophysin expression, but with 10 fold less potency than particles from e3/3 mice. Conclusions: Taken together these data suggest that the low levels of astrocytic apoE/ cholesterol secreted by e4 carriers may directly contribute to the disease progression by reducing apoE’s capacity to promote synaptic repair and Ab clearance. O2-04-03
APOE GENOTYPE AND AMYLOID BETA EFFECTS ON COGNITION ARE MEDIATED BY CELL INJURY (TAU) AND DEATH (PROGRESSIVE ATROPHY)
Charles DeCarli, Owen Carmichael, Danielle Harvey, Evan Fletcher, Dan Mungas, University of California at Davis, Sacramento, CA, USA. Contact e-mail: [email protected] Background: The amyloid hypothesis suggests a primary role for Ab, although clinical symptoms are most closely associated with neurofibrillary formation and neuronal injury and loss. We hypothesized that CSF tau would therefore mediate the effect of CSF Ab on cognitive performance (Figure). Methods: 313 subjects from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) for whom baseline CSF, repeated MRI and repeated Cognitive measures were evaluated. Subjects included 70 AD, 152, MCI and 91 Cognitively normal individuals mean age 74.8 þ 7.0 years. Baseline brain and hippocampal volumes were calculated as well as yearly rates of both measures using a fluid flow deformation method to determine jacobian determinant expansion or contraction for each image voxel. Cognitive measures included 1-year change in delayed story recall and ADAS-Cog. Multiple regression analysis was used to systematically test the effects of CSF Ab, CSF Tau, baseline and change in brain volume
on change in cognition at 1 year. Results: Significant associations were found between the rate of change of cognitive measures and ApoE4 genotype, CSF Ab, CSF Tau, baseline and rate of whole brain atrophy adjusting for age, education and gender (see table). The impact of CSF Ab remained significantly associated with change in cognitive measures in a multiple regression model that included both CSF Ab and ApoE genotype (p <0.0001). CSF Tau was also significantly associated with change in delayed story recall (p¼0.0002) and ADAS-Cog (p<0.0001) when added to the model. In a model predicting change in ADAS-Cog which included baseline and change in whole brain volume as well as CSF Tau and Ab, CSF Tau (p<0.0002), baseline, longitudinal brain atrophy (p<0.0001), but not CSF Ab were significantly associated with change in ADAS-Cog. Conversely, in a model predicting change in delayed story recall, CSF Ab (p < 0.0001), CSF Tau (p¼0.013), baseline hippocampus (p < 0.0001), change in hippocampal (p ¼0.016) and brain volume (p<0.0011) were each significantly associated with rate of change in delayed story recall. Conclusions: CSF Ab has both direct and mediated effects on specific cognitive domains. Reductions in both CSF Ab and CSF tau, therefore, should be considered good markers of therapeutic efficacy in AD clinical trials.
O2-04-04
CHOLESTEROL IN AMYLOID PLAQUES: ANALYSIS BY LASER CAPTURE MICRODISSECTION COMBINED WITH MASS SPECTROMETRY
Maı¨ Panchal1, Jacqueline Loeper2, Claire Perruchini3, Adina Lazar3, Heidi Vitrac3, Denis Pompon2, Charles Duyckaerts3, 1Hoˆpital de la Salpeˆtrie`re, 75013 Paris, France; 2CNRS-CGM, Gif-sur-Yvette, France; 3Hoˆpital de la Salpeˆtrie`re, Paris, France. Contact e-mail: [email protected] Background: The presence of senile plaques (SP) in the brain is one of the pathological hallmarks of Alzheimer’s disease (AD). Extensive knowledge of the protein components of the SP has been acquired over the years but the lipids associated with amyloid beta-peptide (Ab) deposits remain unknown. Many evidences suggest that cholesterol contributes to the pathogenesis of AD. Two studies have reported that SP were enriched in cholesterol. We provided data suggesting that these results were obtained with poorly specific methods (Lebouvier et al. 2009). The presence of cholesterol in the senile plaque remains to be demonstrated. Methods: Experiments were performed on frozen brain sections (10 um-thick sections from samples of first temporal gyrus) from three sporadic Braak stage
Oral O2-04: Disease Mechanisms: APOE VI AD cases with numerous amyloid cortical plaques. Laser capture microdissection (LCM) of SPs and of Ab free neuropil was performed immediately after Ab immunohistochemistry with short incubation times. The quantity of Ab peptide in an identical volume of Ab-free neuropil and of senile plaque core was compared. After lipid extraction, the samples were analyzed by liquid chromatography combined with mass spectrometry (LC-MS), using cholesterol standards. Results: We demonstrated a statistically significant increase of cholesterol in SPs versus neuropil. These data combined with the known presence of ApoE, the cholesterol transporter, in the SPs suggest that cholesterol plays a role in the formation and/or progression of the plaques. Conclusions: LCM allowed us to isolate a pure preparation of amyloid core. This preparation was enriched in cholesterol when compared to plaque-free neuropil. This methodology can be extended to analyze other pathological structures in various neurodegenerative disorders.
O2-04-05
NOVEL MECHANISM WHERE APOE MIMETICS ACTIVATE PP2A ACTIVITY AND REDUCE ALZHEIMER’S PATHOLOGY IN THREE DIFFERENT TRANSGENIC MODELS
Michael P. Vitek1, Dale J. Christensen1, Donna Wilcock2, Jessica Oddo1, Nastaran Gharkholonarehe2, Nobutaka Ohkubo2, Kazuko Toku2, William E. Van Nostrand3, Fengqiao Li1, Carol A. Colton2, 1Cognosci, Research Triangle Park, NC, USA; 2Duke University Medical Center, Durham, NC, USA; 3Stony Brook University, Stony Brook, NY, USA. Contact e-mail: [email protected] Background: The second largest risk factor for AD is APOE genotype, where APOE4 is also associated with lower apoE levels, more severe brain pathology and inflammation. We reported that small peptides corresponding to the receptor-binding region of apoE could mimic the anti-inflammatory activity of the apoE holoprotein (Lynch et al. 2003). When given systemically after brain trauma and/or hemorrhage, these apoE-mimetics greatly improved behavioral outcomes and neuronal survival (Laskowitz et al. 2007, James et al. 2008). Methods: To understand this protective activity, we employed biotinylated-apoE-mimetics and affinity purified I2PP2A as a major binding protein in mouse and human brains. I2PP2A is a natural inhibitor of PP2A, the key protein phosphatase associated with dephosphorylation of many important proteins. Addition of apoE-mimetics significantly stimulates PP2A’s phosphatase activity resulting in dramatic inhibition of tumor necrosis factor alpha (TNFa) release following stimulation with lipopolysaccharide (LPS). Similarly, siRNA to I2PP2A also reduces phospho-protein and TNFa levels following LPS, and these reductions are not further increased with added apoE-mimetics. Results: Since PP2A can greatly reduce phospho-tau associated with neurofibrillary tangle-like structures (NFTs), we tested the ability of peripherally administered apoE-mimetics to reduce phospho-tau AT8-immunoreactive staining in the brains of transgenic mice. After nine months, JNPL3 (P301L tau) mice on a NOS2-/- background (Colton et al. unpublished), Tg2576 (APPsw) on a NOS2-/- background (Colton et al. 2006), and APP-SwDI on a NOS2-/- background (Wilcock et al. 2008) were treated with apoE-mimetics for three months and brain pathology was evaluated. In each case, an obvious reduction in AT8-labeled NFT-like structures was observed in the apoE-mimetic treated animals. Additionally, in APP-Sw/NOS2-/- and APP-SwDI/NOS2-/- mice treated with apoE-mimetics, there was also a clear reduction in Abeta-immunostained amyloid deposits. Since they also improve outcomes after brain hemorrhage, we are currently testing the effect of apoE-mimetics on Abeta-immunized APP-transgenics, which show increased incidence of microhemorrhage. Conclusions: In addition to replacing the lost function of lowered apoE levels, apoE-mimetics cross the blood brain barrier to bind I2PP2A and antagonize this inhibitor, resulting in activation of PP2A. Increased PP2A activity reduces phospho-tau levels and amyloid deposits in multiple Alzheimer’s transgenics suggesting the use of apoE-mimetics as therapeutics in AD.
O2-04-06
P111
GRB-ASSOCIATED BINDING PROTEIN 2 (GAB2) INTERACTS WITH APOE TO ALTER RISK OF LATE-ONSET ALZHEIMER’S DISEASE
Gary W. Beecham1, Adam C. Naj1, Guiqing Cai2, Yuji Kajiwara2, Vahram Haroutunian2, Ioanna Konidari1, Paul Gallins1, Patrice Whitehead1, John R. Gilbert1, Michael A. Slifer1, Harry Gwirstman3, Eden R. Martin1, Joseph Buxbaum2, Jonathan L. Haines4, Margaret A. Pericak-Vance1, 1University of Miami, Miller School of Medicine, Miami, FL, USA; 2Mount Sinai School of Medicine, Department of Psychiatry, New York, NY, USA; 3VA Hospital Medical Center, Department of Psychiatry, Nashville, TN, USA; 4Vanderbilt University, Center for Human Genetics Research, Nashville, TN, USA. Contact e-mail: [email protected] Background: Other than the apolipoprotein E (APOE) gene, there have been no consistently replicated genetic risk factors for late-onset Alzheimer disease (LOAD). Numerous candidate genes have been proposed but validation of genetic association signals has proven difficult. One such candidate gene is GRB-associated binding protein 2 (GAB2). GAB2, associated with LOAD in APOE-4 carriers in a published genome-wide association study (p-value ¼ 9 x 10-11), is over expressed in LOAD brain, and has been shown to influence Alzheimer’s neuropathology. Methods: To investigate the role of GAB2 in LOAD we examined 22 SNPs across the GAB2 gene in a large cohort of 876 LOAD cases and 804 cognitive controls. Cases and controls were gender and age matched, and affection status was confirmed through either 3MS or MMSE batteries. Genotypes were obtained from Illumina HumanHap beadchips and extensive quality-control measures were implemented, including correction for population substructure. Association was tested under an additive model and interaction with APOE was considered in the model. IMPUTE was used to infer genotypes at the rs2373115 SNP, the SNP with strong association in the previous association study. Results: We confirm the association of GAB2 with LOAD. Of the 22 SNPs genotyped, 19 showed significant interaction with APOE (p-values ¼ 0.04 to 0.004; odds ratio ¼ 1.5 to 1.9 for the interaction term). The additive effect of GAB2 was not significant, even after controlling for APOE genotype. The rs2373115 SNP was successfully imputed and also shows significant interaction with apoE genotypes (p-value¼0.015; OR¼1.63). The interaction appears to be largely driven by the APOE-4 positive controls; the e4 positive controls have an excess of the major GAB2 homozygote (p-value ¼ 0.0013), implying that the genotype mitigates the effect of the e4 allele. Conclusions: We have replicated the GAB2 interaction with APOE, showing statistical significance in a large cohort. This analysis confirms that GAB2 is an excellent candidate gene for late-onset Alzheimer disease, and highlights the need for further delineation of interaction effects in the search for genetic risk factors.
O2-04-07
MOST RAPID COGNITIVE DECLINE IN APOE4 NEGATIVE ALZHEIMER’S DISEASE WITH EARLY ONSET
Wiesje M. van der Flier, Annelies E. van der Vlies, Esther L. Koedam, Yolande A. L. Pijnenburg, Jos W. R. Twisk, Philip Scheltens, VU Medical Center, Amsterdam, Netherlands. Contact e-mail: [email protected] Background: We aimed to compare the rate of cognitive decline in patients with early and late onset Alzheimer’s Disease (AD) and to investigate the potentially modifying influence of APOE genotype. Methods: We included 99 patients with early onset AD (age 65 years) and 192 patients with late onset AD (age >65 years) who had at least 2 MMSE scores (range 2-14) obtained at least one year apart. Linear mixed models were performed to investigate the rate of cognitive decline dependent on age-at-onset and APOE genotype. Results: Mean (sd) age for patients with early onset was 57.7 (4.5) years, and 74.5 (5.1) for patients with late onset. Age-at-onset was not associated with baseline MMSE (b(SE)¼ 0.8 (0.5), p¼ 0.14). However, patients with early onset showed faster decline on the MMSE of (b(SE)) 2.4 (0.1) points/year, whereas those with late onset showed decline of 1.7 (0.1) points/year