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The butyrylcholinesterase gene is neither independently nor synergistically associated with late-onset AD in clinic- and community-based populations
Neuroscience Letters 249 (1998) 115–118
The butyrylcholinesterase gene is neither independently nor synergistically associated with late-onset AD in clinicand community-based populations F. Crawford a ,*, D. Fallin a, Z. Suo a, L. Abdullah a, M. Gold b, A. Gauntlett a, R. Duara c, M. Mullan a a
Roskamp Laboratories, University of South Florida, Tampa, FL 33613, USA b University of South Florida Memory Disorder Clinic, Tampa, FL USA c Mount Sinai Memory Disorder Clinic, University of Miami, Miami, FL USA Received 3 April 1998; accepted 11 May 1998
Abstract The K variant of the butyrylcholinesterase gene (BChE) was recently found to occur at an increased frequency in a late onset Alzheimer’s disease (AD) population, specifically in individuals carrying the e4 allele of the apolipoprotein E (APOE) gene. This suggested synergy between these two genes resulting in an increased risk of late-onset AD. We have genotyped 62 communitybased and 329 clinic-based AD cases, and 201 community-based controls at BChE and APOE and find no independent association between BChE and AD nor interaction with APOE in risk for AD in either our clinic or community-based samples. 1998 Published by Elsevier Science Ireland Ltd. All rights reserved
Keywords: Alzheimer’s Disease; Genetic association; Butyrylcholinesterase; K variant; Apolipoprotein E
Since the confirmation of the apolipoprotein E (APOE) gene as a risk factor for late onset Alzheimer’s disease (LOAD) [15,18] the identification of other genes which may confer independent or additional risk has been the focus of a number of studies. These have included genes already known to play a role in early-onset AD–presenilin 1 (PS-1)[20], genes whose products are implicated as candidates in AD pathology – alpha-1 antichymotrypsin (a 1ACT) [9], and those encoding proteins known to relate to APOE, such as the genes for the very low density lipoprotein receptor (VLDL-R) [16] or the low density lipoprotein receptor-related protein (LRP) [12]. While initial reports of positive associations at each of these loci have been encouraging, subsequent confirmation has been lacking [1–5,17], with the discrepancies often being attributed to sampling bias.
* Corresponding author. Tel.: +1 813 9793538; fax: +1 813 9793548.
Synergy between the K variant of the butyrylcholinesterase (BChE) gene and the APOE gene was recently reported by Lehmann and colleagues [11] in a late-onset AD population. While the frequency of the K variant was elevated in 74 subjects with LOAD compared to 104 control subjects, the association was limited to those AD cases who carried one or more copies of the APOEe4 allele. The BChE gene is of interest in AD given its association with many aspects of AD pathology including compact b-amyloid plaques, tangles and amyloid angiopathy [13,6], and because it has recently been suggested to be involved in the adoption of b-pleat formation by the b-amyloid peptide [7]. The K variant reduces the activity of the enzyme by approximately one third [10], indicating a possible mechanism by which this functional polymorphism could alter risk for AD. However, one would predict that such a decrease in acetylcholine catabolism would, if anything, be protective, yet the opposite was reported. For this reason, we investigated the occurrence of the BChE-K variant in both communityand clinic-based samples of late onset AD cases compared
0304-3940/98/$19.00 1998 Published by Elsevier Science Ireland Ltd. All rights reserved PII S0304- 3940(98) 00423- 6
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F. Crawford et al. / Neuroscience Letters 249 (1998) 115–118
Table 1 BChE allele and genotype frequencies for late-onset AD cases from community- and clinic-based samples compared to community-based controls Controls
AD Community
Clinic
a
Odds ratio
Odds ratio (C.I.)
Odds ratio
Odds ratio (C.I.)
BChE genotype +/+ K/+ K/K n
0.741 0.229 0.030 201
0.823 0.161 0.016 62 P = 0.394*
1 0.59 (0.25–1.4) 0.004 (10−15–1.6 × 1010)
0.684 0.289 0.027 329 P = 0.313*
1 1.33 (0.88–2.02) 0.90 (0.30–2.7)
BChE alleles + K n
0.856 0.144 402
0.903 0.097 124 P = 0.160*
1 0.64 (0.33–1.2)
0.828 0.172 658 P = 0.236*
1 1.23 (0.87–1.7)
*x2 comparison to controls. aOdds ratios were calculated through logistic regression controlling for age and gender.
with community-based control individuals, all previously genotyped at the APOE locus. We have genotyped 62 community-based AD cases (51.6% men; average age at onset = 76.4, SD = 7.5), 329 clinic-based AD cases (54.2% men; average age at onset = 72.4, SD = 6.0) and 201 aged controls (39.7% men; average age = 72.33, SD = 7.08) at APOE and BChE. The community-based AD cases and controls were recruited as part of a community screen for dementia among those aged 60 years or above in the Miami-Dade County area of Florida. Details of recruitment and screening have previously been described by Fallin et al. [4]. Participants from residential elderly communities were recruited through invitation in the local media and through community leaders. Community members scoring well on the screen were included in the control population, while those scoring poorly were asked to undergo further examination at the Mount Sinai
Memory Disorder Clinic, and individuals subsequently diagnosed with probable or possible AD (according to NINCDS–ADRDA criteria), were included in the case group. Those individuals diagnosed with other dementias or those with indeterminate diagnoses were not included in this study. Samples in the clinic-based AD group were collected as part of a multi-center clinical trial and all met NINCDS-ADRDA criteria for probable or possible AD. As the age and gender distributions were significantly different in normals compared to cases, all odds ratios were computed controlling for gender and age. APOE genotyping was carried out by PCR amplification (94°C, 68°C, 72°C; 30-s cycling for 40 cycles) and CfoI digestion using previously-described primers and scoring methods [19]. The BChE-K variant was detected by PCR amplification (94°C, 57°C, 72°C; 30-s cycling for 35 cycles) using primers published by Jensen and colleagues [8] which
Table 2 Risk for BChE-K carriers stratified by APOE-e4 carrier status for clinic and community-based samples Controls
AD Community a
Clinic
Odds ratio
Odds ratio (C.I.)
Odds ratio
Odds ratio (C.I.)
e4−
K carriers +/+ n
0.241 0.759 158
0.118 0.882 34
0.42 (0.14–1.27) 1 P = 0.18
0.374 0.626 107
1.89 (1.10–3.22) 1 P = 0.028
e4+
K carriers +/+ n
0.326 0.674 43
0.250 0.750 28
0.69 (0.24–2.01) 1 P = 0.67 common ORa = 0.53 [0.27–1.06] P . 0.50b
0.288 0.712 222
0.84 (0.42–1.69) 1 P = 0.758 Common ORa = 1.4 (0.89–2.20) P . 0.05b
a
Mantel-Haenszel odds ratio and test-based 95% confidence limits. **Test for homogeneity of the odds ratio indicating level of significance of interaction.
117
F. Crawford et al. / Neuroscience Letters 249 (1998) 115–118 Table 3
Odds ratios for carriers of the BChE-K variant, the APOE-e4, or both compared to those with neither among all subjects, and among those above age 75 in both community- and clinic-based samples Subjects . 75yrs
All Subjects BChE-K Community
n Clinic
n
APOE-e4
− + − +
− − + +
− + − +
− − + +
OR
CI
OR
CI
1 0.43 2.92 2.35 62 AD, 201 controls 1 1.85 9.59 7.96 329 AD, 201 controls
– 0.14–1.34 1.41–6.02 0.82–6.69
1 1.03 2.36 0.50 31 AD, 65 controls 1 2.31 6.17 5.98 102 AD, 65 controls
– 0.27–4.04 0.74–7.50 0.05–5.24
in the presence of the K variant create a MaeIII restriction site. The BChE allele and genotype frequencies for our clinic and community-based populations are displayed in Table 1. There is no significant difference in these frequencies between either case group and controls. Further, the oddsratio trend for the clinic-based cases is in the opposite direction from the community-based AD sample. Because APOE e4 is a known risk factor for late-onset AD which may confound or interact with BChE association, we then stratified the populations by e4 carrier status as shown in Table 2. These analyses also show opposite directions for risk between the clinic and community-based AD samples. Further, the common odds ratio and chi-square statistics for each case group is not significant. A test of the homogeneity of the odds ratios (OR) across strata also shows no interaction between APOE and BChE in the communitybased AD group (P . 0.50), but indicates possible interaction within the clinic-based analyses (0.05 , P , 0.10). Within these clinic-based cases and community controls, a likelihood ratio test between a logistic regression model including APOE e4 carrier status, BChE-K carrier status, and their interaction (and age and gender as controlling factors) versus a model without an interactive term, also indicates a marginally-significant contribution by adding an interactive term (0.05 , P , .10). The nature of this possible interaction is apparent in Table 2 showing an OR . 1 among non e4 carriers in the clinic sample and an OR , 1 among those carrying an APOE e4. This is an opposite effect to that reported by Lehmann and colleagues which found significant synergistic association of the BChE-K variant in the e4 positive carriers. This can also be examined by calculating the odds ratios for those who carry one or the other allele (compared to those who carry neither) and for those who carry both. Should a synergistic interaction between these factors exist, the OR for carrying a risk allele at both genes should be largely greater than the predicted OR for the combination of each separately. These calculations (shown in Table 3) indicate that no such interaction exists in these populations. Finally, the previous
– 1.07–3.23 5.78–15.9 4.09–15.4
– 0.87–6.02 2.57–14.8 1.78–20.0
report suggested that the association with BChE-K and AD, and the synergistic interaction with APOE-e4 were enhanced in the above age 75 individuals. We do not see an association in this .75 age group in any of the analyses presented, and have shown this for the final set of analyses reported in Table 3. The failure to replicate the results of Lehmann and colleagues [11] in populations which are comparable in terms of age and ethnicity, suggests differences in sampling strategy, or else reflects a true genetic difference between the populations. We have previously reported the distortion of allele frequencies due to ascertainment bias [14]. This is true in the current study as well – the BChE frequencies are significantly different between community and clinic AD samples. Recruitment of cases for the Lehmann study is probably most comparable to our clinic-based sample as theirs is specifically recruited for the Oxford Project to investigate memory and aging (the OPTIMA project). The difference in findings may also be due to true genetic differences between populations as BChE frequencies for our control population are most similar to the OPTIMA case population, while our community-based cases are most similar to their controls. The most likely conclusion, however, is that no true synergistic effect exists but that stratification by a known genetic risk factor among clinic samples may lead to spurious associations with further genes. This work was supported by the generosity of Mr. and Mrs. R. Roskamp, by NIH grant RO1-AG12412 and Sandoz Pharmaceuticals. [1] Cai, X., Stanton, J., Fallin, D., Hoyne, J., Duara, R., Gold, M., Sevush, S., Scibelli, P., Crawford, F. and Mullan, M., No association between the intronic preselnilin-1 polymorphism and Alzheimer’s disease in clinic and population-based samples, Am. J. Med. Genet. (Neuropsychiatric genet.), 74 (1997) 202– 203. [2] Chung, H., Roberts, C., Greenberg, S., Rebeck, W., Christie, R., Wallace, R., Jacob, H. and Hyman, B., Lack of association of trinucleotide repeat polymorphisms in the very-low-density lipoprotein receptor gene with Alzheimer’s disease, Ann. Neurol., 6 (1996) 800–803.
118
F. Crawford et al. / Neuroscience Letters 249 (1998) 115–118
[3] Fallin, D., Reading, S., Schinka, J., Hoyne, J., Scibelli, P., Gold, M., Crawford, F. and Mullan, M., No interaction between the APOE and the alpha-1-antichymotrypsin genes on risk for Alzheimer’s disease, Am. J. Med. Genet., 74 (2) (1997) 192–194. [4] Fallin, D., Gauntlett, A., Scibelli, P., Cai, X., Duara, R., Gold, M., Crawford, F. and Mullan, M., No association between the VLDL-R gene and late-onset Alzheimer’s disease nor interaction with the APOE gene in population-based and clinic samples, Genet. Epidemiol., 14 (1997) 299–305. [5] Fallin, D., Kundtz, A., Town, T., Gauntlett, A., Duara, R., Barker, W., Crawford, F. and Mullan, M., No association between the low density lipoprotein receptor-related protein (LRP) gene and late-onset Alzheimer’s disease in a community-based sample, Neurosci. Lett., 233 (1997) 145–147. [6] Gomez-Ramos, P., Bouras, C. and Moran, M., Ultrastructural localization of butyrylcholinesterase on neurofibrillary degeneration sites in the brains of aged and Alzheimer’s disease patients, Brain Res., 640 (1994) 17–24. [7] Guillozet, A., Smiley, J., Mash, D. and Mesulam, M., Butyrylcholinesterase in the life cycle of amyloid plaques, Ann Neurol., 42 (6 )(1997) 909–918. [8] Jensen, F., Nielsen, L. and Schwartz, M., Detection of the plasma cholinesterase K variant by PCR using an amplification-created restriction site, Hum. Hered., 46 (1996) 26–31. [9] Kamboh, M., Sanghera, D., Rerrell, R. and DeKosky, S., APOE 4-associated Alzheimer’s disease risk is modified by alpha-1antichymotrypsin polymorphism, Nat. Genet., 10 (1995) 486– 488. [10] La Du, B.N., Bartels, C.F., Nogueira, C.P., Hajra, A., Lightstone, H., Van der Spek, A. and Lockridge, O., Phenotypic and molecular biological analysis of human butyrylcholinesterase variants, Clin. Biochem., 23 (5) (1990) 423–431. [11] Lehmann, D.J., Johnston, C. and Smith, A.D., Synergy between the genes for butyrylcholinesterase K variant and apolipoprotein E4 in late-onset confirmed Alzheimer’s disease, Hum. Mol. Genet., 6 (11) (1997) 1933–1936. [12] Lendon, C., Talbot, C., Craddock, N., Jan, S.W., Wragg, M.,
[13]
[14]
[15]
[16]
[17]
[18]
[19] [20]
Morris, J. and Goate, A., Genetic association studies between dementia of the Alzheimer’s type and three receptors for apolipoprotein E in a Caucasian population, Neurosci. Lett., 222 (1997) 187–190. Mesulam, M. and Geula, C., Butyrylcholinesterase reactivity differentiates the amyloid plaques of aging from those of dementia, Ann. Neurol., 31 (1994) 722–727. Mullan, M., Scibelli, P., Duara, R., Fallin, D., Gold, M., Schinka, J., Hoyne, J., Osborne, A., Sevush, S. and Crawford, F., Familial and population-based studies of apolipoprotein E and Alzheimer’s disease, Ann. NY. Acad. Sci., 802 (1996) 16–26. National Institute of Aging/Alzheimer’s Association Working Group, Apolipoprotein E Genotyping in Alzheimer’s Disease, Lancet, 347 (1996) 1091–1095. Okuizumi, K., Onedera, O., Seki, K., Namba, Y., Ikeda, K., Yamamoto, T., Seki, K., Ueki, A., Nanko, S., Tanaka, H., Takahashi, H., Oyanagi, K., Mizusawa, H., Kanazawa, I. and Tsuji, S., Genetic association of very low density lipoprotein (VLDL) receptor gene with sporadic Alzheimer’s disease, Nat. Genet., 11 (1995) 207–209. Pritchard, M.L., Saunders, P.C., Gaskell, G.W., Small, G.W., Conneally, P.M., Rosi, B., Yamaoka, L.H., Rose, A.D., Haines, J.L., Pericak-Vance, M.A. and Risch, N., No association between very low density lipoprotein receptor (VLDL-R) and Alzheimer’s disease in American Caucasians, Neurosci Lett., 209 (1996) 105–108. Strittmatter, W.H., Saunders, A.M., Schmechel, D., Pericak Vance, M., Enghild, I., Salvesen, G. and Roses, A., Apolipoprotein E: high avidity binding to b-amyloid and increased frequency of type 4 allele in late onset Alzheimer’s Disease, Proc. Natl. Acad Sci. (USA), 90 (1993) 1977–1981. Wenham, P., Price, W. and Blundell, G., Apolipoprotein E genotyping by one-stage PCR, Lancet, 337 (1991) 1158–1159. Wragg, M., Hutton, M. and Talbot, C., Genetic association between intronic polymorphism in presenilin-1 gene and lateonset Alzheimer’s disease. Alzheimer’s Disease Collaborative Group, Lancet, 347 (1996) 509–512.
The butyrylcholinesterase gene is neither independently nor synergistically associated with late-onset AD in clinicand community-based populations F. Crawford a ,*, D. Fallin a, Z. Suo a, L. Abdullah a, M. Gold b, A. Gauntlett a, R. Duara c, M. Mullan a a
Roskamp Laboratories, University of South Florida, Tampa, FL 33613, USA b University of South Florida Memory Disorder Clinic, Tampa, FL USA c Mount Sinai Memory Disorder Clinic, University of Miami, Miami, FL USA Received 3 April 1998; accepted 11 May 1998
Abstract The K variant of the butyrylcholinesterase gene (BChE) was recently found to occur at an increased frequency in a late onset Alzheimer’s disease (AD) population, specifically in individuals carrying the e4 allele of the apolipoprotein E (APOE) gene. This suggested synergy between these two genes resulting in an increased risk of late-onset AD. We have genotyped 62 communitybased and 329 clinic-based AD cases, and 201 community-based controls at BChE and APOE and find no independent association between BChE and AD nor interaction with APOE in risk for AD in either our clinic or community-based samples. 1998 Published by Elsevier Science Ireland Ltd. All rights reserved
Keywords: Alzheimer’s Disease; Genetic association; Butyrylcholinesterase; K variant; Apolipoprotein E
Since the confirmation of the apolipoprotein E (APOE) gene as a risk factor for late onset Alzheimer’s disease (LOAD) [15,18] the identification of other genes which may confer independent or additional risk has been the focus of a number of studies. These have included genes already known to play a role in early-onset AD–presenilin 1 (PS-1)[20], genes whose products are implicated as candidates in AD pathology – alpha-1 antichymotrypsin (a 1ACT) [9], and those encoding proteins known to relate to APOE, such as the genes for the very low density lipoprotein receptor (VLDL-R) [16] or the low density lipoprotein receptor-related protein (LRP) [12]. While initial reports of positive associations at each of these loci have been encouraging, subsequent confirmation has been lacking [1–5,17], with the discrepancies often being attributed to sampling bias.
* Corresponding author. Tel.: +1 813 9793538; fax: +1 813 9793548.
Synergy between the K variant of the butyrylcholinesterase (BChE) gene and the APOE gene was recently reported by Lehmann and colleagues [11] in a late-onset AD population. While the frequency of the K variant was elevated in 74 subjects with LOAD compared to 104 control subjects, the association was limited to those AD cases who carried one or more copies of the APOEe4 allele. The BChE gene is of interest in AD given its association with many aspects of AD pathology including compact b-amyloid plaques, tangles and amyloid angiopathy [13,6], and because it has recently been suggested to be involved in the adoption of b-pleat formation by the b-amyloid peptide [7]. The K variant reduces the activity of the enzyme by approximately one third [10], indicating a possible mechanism by which this functional polymorphism could alter risk for AD. However, one would predict that such a decrease in acetylcholine catabolism would, if anything, be protective, yet the opposite was reported. For this reason, we investigated the occurrence of the BChE-K variant in both communityand clinic-based samples of late onset AD cases compared
0304-3940/98/$19.00 1998 Published by Elsevier Science Ireland Ltd. All rights reserved PII S0304- 3940(98) 00423- 6
116
F. Crawford et al. / Neuroscience Letters 249 (1998) 115–118
Table 1 BChE allele and genotype frequencies for late-onset AD cases from community- and clinic-based samples compared to community-based controls Controls
AD Community
Clinic
a
Odds ratio
Odds ratio (C.I.)
Odds ratio
Odds ratio (C.I.)
BChE genotype +/+ K/+ K/K n
0.741 0.229 0.030 201
0.823 0.161 0.016 62 P = 0.394*
1 0.59 (0.25–1.4) 0.004 (10−15–1.6 × 1010)
0.684 0.289 0.027 329 P = 0.313*
1 1.33 (0.88–2.02) 0.90 (0.30–2.7)
BChE alleles + K n
0.856 0.144 402
0.903 0.097 124 P = 0.160*
1 0.64 (0.33–1.2)
0.828 0.172 658 P = 0.236*
1 1.23 (0.87–1.7)
*x2 comparison to controls. aOdds ratios were calculated through logistic regression controlling for age and gender.
with community-based control individuals, all previously genotyped at the APOE locus. We have genotyped 62 community-based AD cases (51.6% men; average age at onset = 76.4, SD = 7.5), 329 clinic-based AD cases (54.2% men; average age at onset = 72.4, SD = 6.0) and 201 aged controls (39.7% men; average age = 72.33, SD = 7.08) at APOE and BChE. The community-based AD cases and controls were recruited as part of a community screen for dementia among those aged 60 years or above in the Miami-Dade County area of Florida. Details of recruitment and screening have previously been described by Fallin et al. [4]. Participants from residential elderly communities were recruited through invitation in the local media and through community leaders. Community members scoring well on the screen were included in the control population, while those scoring poorly were asked to undergo further examination at the Mount Sinai
Memory Disorder Clinic, and individuals subsequently diagnosed with probable or possible AD (according to NINCDS–ADRDA criteria), were included in the case group. Those individuals diagnosed with other dementias or those with indeterminate diagnoses were not included in this study. Samples in the clinic-based AD group were collected as part of a multi-center clinical trial and all met NINCDS-ADRDA criteria for probable or possible AD. As the age and gender distributions were significantly different in normals compared to cases, all odds ratios were computed controlling for gender and age. APOE genotyping was carried out by PCR amplification (94°C, 68°C, 72°C; 30-s cycling for 40 cycles) and CfoI digestion using previously-described primers and scoring methods [19]. The BChE-K variant was detected by PCR amplification (94°C, 57°C, 72°C; 30-s cycling for 35 cycles) using primers published by Jensen and colleagues [8] which
Table 2 Risk for BChE-K carriers stratified by APOE-e4 carrier status for clinic and community-based samples Controls
AD Community a
Clinic
Odds ratio
Odds ratio (C.I.)
Odds ratio
Odds ratio (C.I.)
e4−
K carriers +/+ n
0.241 0.759 158
0.118 0.882 34
0.42 (0.14–1.27) 1 P = 0.18
0.374 0.626 107
1.89 (1.10–3.22) 1 P = 0.028
e4+
K carriers +/+ n
0.326 0.674 43
0.250 0.750 28
0.69 (0.24–2.01) 1 P = 0.67 common ORa = 0.53 [0.27–1.06] P . 0.50b
0.288 0.712 222
0.84 (0.42–1.69) 1 P = 0.758 Common ORa = 1.4 (0.89–2.20) P . 0.05b
a
Mantel-Haenszel odds ratio and test-based 95% confidence limits. **Test for homogeneity of the odds ratio indicating level of significance of interaction.
117
F. Crawford et al. / Neuroscience Letters 249 (1998) 115–118 Table 3
Odds ratios for carriers of the BChE-K variant, the APOE-e4, or both compared to those with neither among all subjects, and among those above age 75 in both community- and clinic-based samples Subjects . 75yrs
All Subjects BChE-K Community
n Clinic
n
APOE-e4
− + − +
− − + +
− + − +
− − + +
OR
CI
OR
CI
1 0.43 2.92 2.35 62 AD, 201 controls 1 1.85 9.59 7.96 329 AD, 201 controls
– 0.14–1.34 1.41–6.02 0.82–6.69
1 1.03 2.36 0.50 31 AD, 65 controls 1 2.31 6.17 5.98 102 AD, 65 controls
– 0.27–4.04 0.74–7.50 0.05–5.24
in the presence of the K variant create a MaeIII restriction site. The BChE allele and genotype frequencies for our clinic and community-based populations are displayed in Table 1. There is no significant difference in these frequencies between either case group and controls. Further, the oddsratio trend for the clinic-based cases is in the opposite direction from the community-based AD sample. Because APOE e4 is a known risk factor for late-onset AD which may confound or interact with BChE association, we then stratified the populations by e4 carrier status as shown in Table 2. These analyses also show opposite directions for risk between the clinic and community-based AD samples. Further, the common odds ratio and chi-square statistics for each case group is not significant. A test of the homogeneity of the odds ratios (OR) across strata also shows no interaction between APOE and BChE in the communitybased AD group (P . 0.50), but indicates possible interaction within the clinic-based analyses (0.05 , P , 0.10). Within these clinic-based cases and community controls, a likelihood ratio test between a logistic regression model including APOE e4 carrier status, BChE-K carrier status, and their interaction (and age and gender as controlling factors) versus a model without an interactive term, also indicates a marginally-significant contribution by adding an interactive term (0.05 , P , .10). The nature of this possible interaction is apparent in Table 2 showing an OR . 1 among non e4 carriers in the clinic sample and an OR , 1 among those carrying an APOE e4. This is an opposite effect to that reported by Lehmann and colleagues which found significant synergistic association of the BChE-K variant in the e4 positive carriers. This can also be examined by calculating the odds ratios for those who carry one or the other allele (compared to those who carry neither) and for those who carry both. Should a synergistic interaction between these factors exist, the OR for carrying a risk allele at both genes should be largely greater than the predicted OR for the combination of each separately. These calculations (shown in Table 3) indicate that no such interaction exists in these populations. Finally, the previous
– 1.07–3.23 5.78–15.9 4.09–15.4
– 0.87–6.02 2.57–14.8 1.78–20.0
report suggested that the association with BChE-K and AD, and the synergistic interaction with APOE-e4 were enhanced in the above age 75 individuals. We do not see an association in this .75 age group in any of the analyses presented, and have shown this for the final set of analyses reported in Table 3. The failure to replicate the results of Lehmann and colleagues [11] in populations which are comparable in terms of age and ethnicity, suggests differences in sampling strategy, or else reflects a true genetic difference between the populations. We have previously reported the distortion of allele frequencies due to ascertainment bias [14]. This is true in the current study as well – the BChE frequencies are significantly different between community and clinic AD samples. Recruitment of cases for the Lehmann study is probably most comparable to our clinic-based sample as theirs is specifically recruited for the Oxford Project to investigate memory and aging (the OPTIMA project). The difference in findings may also be due to true genetic differences between populations as BChE frequencies for our control population are most similar to the OPTIMA case population, while our community-based cases are most similar to their controls. The most likely conclusion, however, is that no true synergistic effect exists but that stratification by a known genetic risk factor among clinic samples may lead to spurious associations with further genes. This work was supported by the generosity of Mr. and Mrs. R. Roskamp, by NIH grant RO1-AG12412 and Sandoz Pharmaceuticals. [1] Cai, X., Stanton, J., Fallin, D., Hoyne, J., Duara, R., Gold, M., Sevush, S., Scibelli, P., Crawford, F. and Mullan, M., No association between the intronic preselnilin-1 polymorphism and Alzheimer’s disease in clinic and population-based samples, Am. J. Med. Genet. (Neuropsychiatric genet.), 74 (1997) 202– 203. [2] Chung, H., Roberts, C., Greenberg, S., Rebeck, W., Christie, R., Wallace, R., Jacob, H. and Hyman, B., Lack of association of trinucleotide repeat polymorphisms in the very-low-density lipoprotein receptor gene with Alzheimer’s disease, Ann. Neurol., 6 (1996) 800–803.
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