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Polymorphism at codon 174 of the prion-like protein gene is not associated with sporadic Alzheimer's disease
Neuroscience Letters 332 (2002) 213–215 www.elsevier.com/locate/neulet
Polymorphism at codon 174 of the prion-like protein gene is not associated with sporadic Alzheimer’s disease Jon Infante a, Javier Llorca b, Lucı´a Rodero a, Enrique Palacio a, Jose´ Berciano a, Onofre Combarros a,* a
Service of Neurology, University Hospital “Marque´s de Valdecilla” (University of Cantabria), 39008 Santander, Spain b Division of Preventive Medicine, University of Cantabria School of Medicine, 39008 Santander, Spain Received 1 August 2002; received in revised form 15 August 2002; accepted 15 August 2002
Abstract Alzheimer’s disease (AD) and prion diseases are associated with the occurrence of protein aggregates called amyloid fibrils, containing the amyloid-b peptide in AD, and a modified form (PrP Sc) of the normal cellular prion protein (PrP c) in prion diseases. PrP c is encoded by the prion protein gene, and a common polymorphism at codon 129 of this gene is a determinant of susceptibility to acquired and sporadic prion diseases but not for sporadic AD. A recently identified novel protein, named Doppel, shares biochemical and structural homology with PrP c. Preliminary evidence in a German population indicates that a polymorphism at codon 174 of the prion-like protein (PRND) gene encoding for Doppel protein is a predisposing factor for both prion diseases and sporadic AD. A case-control study utilizing a clinically well-defined group of 283 sporadic AD patients and 288 control subjects was performed to test this association. The current study does not demonstrate any significant difference in T174M PRND genotype or allele frequencies between AD patients and controls. Our study in the Spanish population argues against the hypothesis that the PRND gene is causally related to AD. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Alzheimer’s disease; Prion-like protein gene; Doppel; Prion
Alzheimer’s disease (AD) and prion diseases such as Creutzfeldt–Jakob disease (CJD) share many similarities, and both are associated with the occurrence of protein aggregates called amyloid fibrils, or plaques [5]. In AD, two types of aggregates are associated with brain damage, fibrillar tangles of the tau protein inside neurons, and amyloid fibrils containing many copies of the 40–42amino-acid amyloid-b peptide outside. In CJD, the normal cellular prion protein (PrP c) is converted in a modified protein (PrP Sc) through a posttranslational process during which it acquires a high b-sheet content [12]. Around 15% of human prion disease is inherited, and all cases to date have been associated with coding mutations in the prion protein (PRNP) gene [17]. No such pathogenic PRNP mutations are present in sporadic and acquired prion disease. However, a common PRNP polymorphism at residue 129 (where methionine or valine can be encoded) is a key determinant of genetic susceptibility to acquired and * Corresponding author. Tel.: 134-942-202-520; fax: 134-942202-655. E-mail address: [email protected] (O. Combarros).
sporadic prion diseases, which occur mostly in homozygous individuals [1,10]. On the basis of the pathophysiologic similarity between prion diseases such as CJD and AD, homozygosity at codon 129 of the PRNP gene could also be important in conferring susceptibility to sporadic AD. However, in a large Spanish case-control analysis comparing AD cases with individuals who were cognitively intact, homozygosity for the methionine or valine alleles at this genetic locus was not a risk factor for sporadic AD, either in itself or interacting with the Apolipoprotein E (APOE) 14 allele [4]. These results were confirmed in an independent Italian study [3]. Transgenetic studies argue that PrP Sc acts as a template upon which PrP c is refolded into a nascent PrP Sc molecule through a process facilitated by another protein (molecular chaperone) [12,15]. Attention has been focused on the identification of PrP c-binding proteins, and recently, a novel protein, named Doppel (Dpl), was identified that shares significant biochemical and structural homology with PrP c [2,6,9]. In specific strains of PrP c-deficient mouse lines, Dpl is overexpressed and causes apoptotic cerebellar cell death that is counteracted and prevented by PrP c, indicating that
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 94 1- 2
J. Infante et al. / Neuroscience Letters 332 (2002) 213–215
214
range 63–99 years) randomly selected from a nursing home; these subjects had complete neurological and medical examinations that showed that they were free of significant illness and had mini mental state examination scores of 28 or more, which were verified by at least one subsequent annual follow-up assessment. Control subject group age and AD group age at onset distributions did differ (P , 0:0001); however, a significantly older control group might only overestimate the effect size, if there were an association between the T174M PRND polymorphism and AD. The controls arose from the same base population as the cases. The AD and control samples were Caucasians originating from a limited geographical area in Northern Spain. The T174M PRND and APOE polymorphisms were determined as described previously [4,14]. Statistical methods: association between dichotomous variables was analyzed with odds ratio, and 95% confidence intervals were estimated by the Cornfield method or the Fisher exact method. Means of quantitative variables were compared using the Student’s t-test. P-values were estimated by chi-square or Fisher exact tests. Interrelations were analyzed by stratification. All statistical analysis were performed with the package Stata Intercooled, version 6 (Stata Corporation, College Station, Texas, USA). The distribution of T174M PRND genotypes and alleles for AD patients and controls were in Hardy–Weinberg equilibrium. As shown in Table 1, there were no statistical differences either in the AD group as a whole or when AD was categorized by age at onset in early-onset (,70 years) and late-onset ($70 years) subsets, when compared to controls. In the total sample and when compared to TT genotype, the odds ratio (OR) for the TM genotype was 1.13 (95% CI ¼ 0:75–1:69), and 0.98 (95% CI ¼ 0:62–1:54) for the MM genotype. Similarly, no significantly different risk of AD was observed when our data set was stratified by gender: in women, the OR for the TM genotype was of 0.98 (95% CI ¼ 0:60–1:60), and 0.85 (95% CI ¼ 0:50–1:47) for the MM genotype; in men, the
these two proteins can act in a common pathway [6,13,16]. Dpl is encoded by the prion-like protein (PRND) gene, 27 kb downstream from the human PRNP gene. Recently, the human PRND gene has been sequenced to determine whether mutations or polymorphisms within PRND play a role in prion diseases or other neurodegenerative disorders [8,11,14]. The major PRND polymorphism observed corresponded to substitution from threonine to methionine at codon 174 (T174M). In sharp contrast with two independent research groups that found no association between this polymorphism and sporadic and acquired CJD [8,11], Schro¨ der et al. [14] provided preliminary evidence that T174M PRND polymorphism was a predisposition factor for both CJD and AD in a German population. Although the number of individuals studied by these authors was very limited (21 sporadic CJD, 21 sporadic AD, and 111 healthy controls), their data showed a 5.1-fold (95% CI ¼ 1:51–17:1, P ¼ 0:007) increased risk of sporadic CJD and a 2.7-fold (95% CI ¼ 0:96–7:64, P ¼ 0:06) increased risk of sporadic AD, in subjects that were M-carriers (TM and MM genotypes). Therefore, we decided to investigate whether the T174M PRND polymorphism was also associated to an increased risk for developing sporadic AD in a large Spanish population. The study included 283 AD patients (69% women; mean age at the time of study 75.8 years, SD 8.9, range 50–98 years; mean age at onset 72.1 years, SD 8.6, range 48–95 years) who met NINCDS/ADRDA criteria for probable AD [7]. All AD cases were defined as sporadic because their family history did not mention any first-degree relative with dementia. AD patients were consecutively admitted to the Department of Neurology, University Hospital “Marque´ s de Valdecilla”, Santander, Spain, from January, 1997, to June 2000. The large majority of patients were living in the community and had been referred by their general practitioner; few had been admitted from hospital wards or nursing home facilities. Control subjects were 288 unrelated individuals (71% women; mean age 80.3 years, SD 7.8,
Table 1 T174M PRND genotype and allele frequencies in AD patients and control subjects a. Genotype, n (%)
AD ,70 years* $ 70 years* Total Controls APOE e4 (2) subjects AD Controls APOE e4 (1) subjects AD Controls a
Allele Frequency
n
TT
TM
MM
T
M
103 180 283 288
17 (16.5) 52 (28.9) 69 (24.4) 74 (25.7)
60 (58.2) 80 (44.4) 140 (49.5) 133 (46.2)
26 (25.3) 48 (26.7) 74 (26.1) 81 (28.1)
0.46 0.51 0.49 0.49
0.54 0.49 0.51 0.51
124 232
30 (24.2) 62 (26.7)
59 (47.6) 107 (46.1)
35 (28.2) 63 (27.2)
0.48 0.50
0.52 0.50
159 56
39 (24.5) 12 (21.4)
81 (50.9) 26 (46.4)
39 (24.6) 18 (32.2)
0.50 0.45
0.50 0.55
n, number of cases; TT, threonine/threonine; TM, threonine/methionine; MM, methionine/methionine; T, threonine; M, methionine; AD, Alzheimer’s disease; *age at onset; APOE 14 (2), no copies of 14; APOE 14 (1), one or two copies of 14.
J. Infante et al. / Neuroscience Letters 332 (2002) 213–215
OR for the TM genotype was of 1.55 (95% CI ¼ 0:75–3:17), and 1.36 (95% CI ¼ 0:59–3:12) for the MM genotype. Next, we split the data based upon APOE carrier status and there was no significant association between the Mcarrying genotypes and the risk of AD in either APOE 14 carriers (TM genotype, OR ¼ 0:96, 95% CI ¼ 0:44–2:08; MM genotype, OR ¼ 0:67, 95% CI ¼ 0:29–1:55) and non-14 carriers (TM genotype, OR ¼ 1:14, 95% CI ¼ 0:67–1:95; MM genotype, OR ¼ 1:15, 95% CI ¼ 0:63–2:09). Our analysis showed the expected association between the APOE 14 alele and AD with an OR of 4.61 (95% CI ¼ 3:14–6:76, P , 0:0001) for carrying one copy of 14, and an OR of 24.32 (95% CI ¼ 6:28–1, P , 0:0001) for carrying two copies of 14. We then examined the influence of T174M PRND genotypes on the age at onset of AD, and no significant variation existed among TT (mean age of 73.3, SD 6.9 years), TM (mean age of 71.2, SD 9.2 years), and MM (mean age of 72.8, SD 9.0 years) genotypes. The present study failed to replicate the findings of Schro¨ der et al. [14], and there were no significant differences in the percentage of patients with AD and controls with the T174M PRND M-carrying genotype (TM and MM genotypes), even after stratifying by age, sex, and APOE carrier status. The previous positive results of Schro¨ der et al. may have arisen by chance due to the very small sample size of sporadic AD cases studied. In the present report we have employed larger numbers of patients and controls compared to that previous study. Alternatively, an interpretation of this discrepancy would be an ethnic difference in AD susceptibility associated with the T174M PRND polymorphism. In fact, it is noteworthy that the difference in M allele frequency in controls produced in our study (51%) is large when compared to the frequency reported by Schro¨ der in a German population (37%). Our data for the M allele frequency in controls concurs with two independent reports in Great Britain (52%) [8] and France (49%) [11], that did not find any association between this polymorphism and CJD. Therefore, the association found in the German AD population might be due to a linkage disequilibrium between the PRND and other susceptibility gene located nearby, and not present in our Spanish patients. Our negative results with PRND polymorphism together with our previously reported failure to detect a significant association between 129 PRNP polymorphism and AD [4], indicates that the prion gene complex comprising PRNP and PRND is not a major locus conferring susceptibility to sporadic AD in the Spanish population. [1] Alperovitch, A., Zerr, I., Pocchiari, M., Mitrova, E., dePedroCuesta, J., Hegyi, I., Collins, S., Kretzschmar, H., vanDuijn, C. and Will, R.G., Codon 129 prion protein genotype and sporadic Creutzfeldt–Jakob disease, Lancet, 353 (1999) 1673–1674.
215
[2] Behrens, A. and Aguzzi, A., Small is not beautiful: antagonizing functions for the prion protein PrP c and its homologue Dpl, Trends Neurosci., 25 (2002) 150–154. [3] Casadei, V.M., Ferri, C., Calabrese, E., Franceschi, M., Veglia, F., Licastro, F., Mariani, C. and Grimaldi, L.M.E., Prion protein gene polymorphism and Alzheimer’s disease: one modulatory trait of cognitive decline? J. Neurol. Neurosurg. Psychiatry, 71 (2001) 279–280. [4] Combarros, O., Sa´ nchez-Guerra, M., Llorca, J., AlvarezArcaya, A., Berciano, J., Pen˜ a, N. and Ferna´ ndez-Viadero, C., Polymorphism at codon 129 of the prion protein gene is not associated with sporadic AD, Neurology, 55 (2000) 593– 595. [5] Ellis, R.J. and Pinheiro, T.J.T., Danger - misfolding proteins, Nature, 416 (2002) 483–484. [6] Mastrangelo, P. and Westaway, D., The prion gene complex encoding PrP c and Doppel: insights from mutational analysis, Gene, 275 (2001) 1–18. [7] McKhaan, G., Drachman, D., Folstein, M., Katzman, R., Price, D. and Stadlan, E.M., Clinical diagnosis of Alzheimer’s disease: report of the NINCDA-ADRDA Work Group under the auspices of Department of Health and Human Services Task Force on Alzheimer’s Disease, Neurology, 34 (1984) 934–944. [8] Mead, S., Beck, J., Dickinson, A., Fisher, E.M.C. and Collinge, J., Examination of the human prion protein-like gene Doppel for genetic susceptibility to sporadic and variant Creutzfeldt–Jakob disease, Neurosci. Lett., 290 (2000) 117–120. [9] Mo, H., Moore, R.C., Cohen, F.E., Westaway, D., Prusiner, S.B., Wright, P.E. and Dyson, H.J., Two different neurodegenerative diseases caused by proteins with similar structures, Proc. Natl. Acad. Sci. USA, 98 (2001) 2352–2357. [10] Palmer, M.S., Dryden, A.J., Hughes, J.T. and Collinge, J., Homozygous prion protein genotype predisposes to sporadic Creutzfeldt–Jakob disease, Nature, 352 (1991) 340–342. [11] Peoch, K., Gue´ rin, C., Brandel, J.P., Launay, J.M. and Laplanche, J.L., First report of polymorphisms in the prion-like protein gene (PRND): implications for human prion diseases, Neurosci. Lett., 286 (2000) 144–148. [12] Prusiner, S.B., Prions, Proc. Natl. Acad. Sci. USA, 95 (1998) 13363–13383. [13] Rossi, D., Cozzio, A., Flechsig, E., Klein, M.A., Ru¨ licke, T., Aguzzi, A. and Weissmann, C., Onset of ataxia and Purkinje cell loss in PrP null mice inversely correlated with Dpl level in brain, EMBO J., 20 (2001) 694–702. [14] Schro¨ der, B., Franz, B., Hempfling, P., Selbert, M., Ju¨ rgens, T., Kretzschmar, H.A., Bodemer, M., Poser, S. and Zerr, I., Polymorphisms within the prion-like protein gene (Prnd) and their implications in human prion diseases: Alzheimer’s disease and other neurological disorders, Hum. Genet., 109 (2001) 319–325. [15] Welch, W.J. and Gambetti, P., Chaperoning brain diseases, Nature, 392 (1998) 23–24. [16] Westaway, D. and Carlson, G.A., Mammalian prion proteins: enigma, variation and vaccination, Trends Biochem. Sci., 27 (2002) 301–307. [17] Windl, O., Dempster, M., Estibeiro, J.P., Lathe, R., de Silva, R., Esmonde, T., Will, R., Springbett, A., Campbell, T.A., Sidle, K.C.L., Palmer, M.S. and Collinge, J., Genetic basis of Creutzfeldt–Jakob disease in the United Kingdom: a systematic analysis of predisposing mutations and allelic variation in the PRNP gene, Hum. Genet., 98 (1996) 259–264.
Polymorphism at codon 174 of the prion-like protein gene is not associated with sporadic Alzheimer’s disease Jon Infante a, Javier Llorca b, Lucı´a Rodero a, Enrique Palacio a, Jose´ Berciano a, Onofre Combarros a,* a
Service of Neurology, University Hospital “Marque´s de Valdecilla” (University of Cantabria), 39008 Santander, Spain b Division of Preventive Medicine, University of Cantabria School of Medicine, 39008 Santander, Spain Received 1 August 2002; received in revised form 15 August 2002; accepted 15 August 2002
Abstract Alzheimer’s disease (AD) and prion diseases are associated with the occurrence of protein aggregates called amyloid fibrils, containing the amyloid-b peptide in AD, and a modified form (PrP Sc) of the normal cellular prion protein (PrP c) in prion diseases. PrP c is encoded by the prion protein gene, and a common polymorphism at codon 129 of this gene is a determinant of susceptibility to acquired and sporadic prion diseases but not for sporadic AD. A recently identified novel protein, named Doppel, shares biochemical and structural homology with PrP c. Preliminary evidence in a German population indicates that a polymorphism at codon 174 of the prion-like protein (PRND) gene encoding for Doppel protein is a predisposing factor for both prion diseases and sporadic AD. A case-control study utilizing a clinically well-defined group of 283 sporadic AD patients and 288 control subjects was performed to test this association. The current study does not demonstrate any significant difference in T174M PRND genotype or allele frequencies between AD patients and controls. Our study in the Spanish population argues against the hypothesis that the PRND gene is causally related to AD. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Alzheimer’s disease; Prion-like protein gene; Doppel; Prion
Alzheimer’s disease (AD) and prion diseases such as Creutzfeldt–Jakob disease (CJD) share many similarities, and both are associated with the occurrence of protein aggregates called amyloid fibrils, or plaques [5]. In AD, two types of aggregates are associated with brain damage, fibrillar tangles of the tau protein inside neurons, and amyloid fibrils containing many copies of the 40–42amino-acid amyloid-b peptide outside. In CJD, the normal cellular prion protein (PrP c) is converted in a modified protein (PrP Sc) through a posttranslational process during which it acquires a high b-sheet content [12]. Around 15% of human prion disease is inherited, and all cases to date have been associated with coding mutations in the prion protein (PRNP) gene [17]. No such pathogenic PRNP mutations are present in sporadic and acquired prion disease. However, a common PRNP polymorphism at residue 129 (where methionine or valine can be encoded) is a key determinant of genetic susceptibility to acquired and * Corresponding author. Tel.: 134-942-202-520; fax: 134-942202-655. E-mail address: [email protected] (O. Combarros).
sporadic prion diseases, which occur mostly in homozygous individuals [1,10]. On the basis of the pathophysiologic similarity between prion diseases such as CJD and AD, homozygosity at codon 129 of the PRNP gene could also be important in conferring susceptibility to sporadic AD. However, in a large Spanish case-control analysis comparing AD cases with individuals who were cognitively intact, homozygosity for the methionine or valine alleles at this genetic locus was not a risk factor for sporadic AD, either in itself or interacting with the Apolipoprotein E (APOE) 14 allele [4]. These results were confirmed in an independent Italian study [3]. Transgenetic studies argue that PrP Sc acts as a template upon which PrP c is refolded into a nascent PrP Sc molecule through a process facilitated by another protein (molecular chaperone) [12,15]. Attention has been focused on the identification of PrP c-binding proteins, and recently, a novel protein, named Doppel (Dpl), was identified that shares significant biochemical and structural homology with PrP c [2,6,9]. In specific strains of PrP c-deficient mouse lines, Dpl is overexpressed and causes apoptotic cerebellar cell death that is counteracted and prevented by PrP c, indicating that
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 94 1- 2
J. Infante et al. / Neuroscience Letters 332 (2002) 213–215
214
range 63–99 years) randomly selected from a nursing home; these subjects had complete neurological and medical examinations that showed that they were free of significant illness and had mini mental state examination scores of 28 or more, which were verified by at least one subsequent annual follow-up assessment. Control subject group age and AD group age at onset distributions did differ (P , 0:0001); however, a significantly older control group might only overestimate the effect size, if there were an association between the T174M PRND polymorphism and AD. The controls arose from the same base population as the cases. The AD and control samples were Caucasians originating from a limited geographical area in Northern Spain. The T174M PRND and APOE polymorphisms were determined as described previously [4,14]. Statistical methods: association between dichotomous variables was analyzed with odds ratio, and 95% confidence intervals were estimated by the Cornfield method or the Fisher exact method. Means of quantitative variables were compared using the Student’s t-test. P-values were estimated by chi-square or Fisher exact tests. Interrelations were analyzed by stratification. All statistical analysis were performed with the package Stata Intercooled, version 6 (Stata Corporation, College Station, Texas, USA). The distribution of T174M PRND genotypes and alleles for AD patients and controls were in Hardy–Weinberg equilibrium. As shown in Table 1, there were no statistical differences either in the AD group as a whole or when AD was categorized by age at onset in early-onset (,70 years) and late-onset ($70 years) subsets, when compared to controls. In the total sample and when compared to TT genotype, the odds ratio (OR) for the TM genotype was 1.13 (95% CI ¼ 0:75–1:69), and 0.98 (95% CI ¼ 0:62–1:54) for the MM genotype. Similarly, no significantly different risk of AD was observed when our data set was stratified by gender: in women, the OR for the TM genotype was of 0.98 (95% CI ¼ 0:60–1:60), and 0.85 (95% CI ¼ 0:50–1:47) for the MM genotype; in men, the
these two proteins can act in a common pathway [6,13,16]. Dpl is encoded by the prion-like protein (PRND) gene, 27 kb downstream from the human PRNP gene. Recently, the human PRND gene has been sequenced to determine whether mutations or polymorphisms within PRND play a role in prion diseases or other neurodegenerative disorders [8,11,14]. The major PRND polymorphism observed corresponded to substitution from threonine to methionine at codon 174 (T174M). In sharp contrast with two independent research groups that found no association between this polymorphism and sporadic and acquired CJD [8,11], Schro¨ der et al. [14] provided preliminary evidence that T174M PRND polymorphism was a predisposition factor for both CJD and AD in a German population. Although the number of individuals studied by these authors was very limited (21 sporadic CJD, 21 sporadic AD, and 111 healthy controls), their data showed a 5.1-fold (95% CI ¼ 1:51–17:1, P ¼ 0:007) increased risk of sporadic CJD and a 2.7-fold (95% CI ¼ 0:96–7:64, P ¼ 0:06) increased risk of sporadic AD, in subjects that were M-carriers (TM and MM genotypes). Therefore, we decided to investigate whether the T174M PRND polymorphism was also associated to an increased risk for developing sporadic AD in a large Spanish population. The study included 283 AD patients (69% women; mean age at the time of study 75.8 years, SD 8.9, range 50–98 years; mean age at onset 72.1 years, SD 8.6, range 48–95 years) who met NINCDS/ADRDA criteria for probable AD [7]. All AD cases were defined as sporadic because their family history did not mention any first-degree relative with dementia. AD patients were consecutively admitted to the Department of Neurology, University Hospital “Marque´ s de Valdecilla”, Santander, Spain, from January, 1997, to June 2000. The large majority of patients were living in the community and had been referred by their general practitioner; few had been admitted from hospital wards or nursing home facilities. Control subjects were 288 unrelated individuals (71% women; mean age 80.3 years, SD 7.8,
Table 1 T174M PRND genotype and allele frequencies in AD patients and control subjects a. Genotype, n (%)
AD ,70 years* $ 70 years* Total Controls APOE e4 (2) subjects AD Controls APOE e4 (1) subjects AD Controls a
Allele Frequency
n
TT
TM
MM
T
M
103 180 283 288
17 (16.5) 52 (28.9) 69 (24.4) 74 (25.7)
60 (58.2) 80 (44.4) 140 (49.5) 133 (46.2)
26 (25.3) 48 (26.7) 74 (26.1) 81 (28.1)
0.46 0.51 0.49 0.49
0.54 0.49 0.51 0.51
124 232
30 (24.2) 62 (26.7)
59 (47.6) 107 (46.1)
35 (28.2) 63 (27.2)
0.48 0.50
0.52 0.50
159 56
39 (24.5) 12 (21.4)
81 (50.9) 26 (46.4)
39 (24.6) 18 (32.2)
0.50 0.45
0.50 0.55
n, number of cases; TT, threonine/threonine; TM, threonine/methionine; MM, methionine/methionine; T, threonine; M, methionine; AD, Alzheimer’s disease; *age at onset; APOE 14 (2), no copies of 14; APOE 14 (1), one or two copies of 14.
J. Infante et al. / Neuroscience Letters 332 (2002) 213–215
OR for the TM genotype was of 1.55 (95% CI ¼ 0:75–3:17), and 1.36 (95% CI ¼ 0:59–3:12) for the MM genotype. Next, we split the data based upon APOE carrier status and there was no significant association between the Mcarrying genotypes and the risk of AD in either APOE 14 carriers (TM genotype, OR ¼ 0:96, 95% CI ¼ 0:44–2:08; MM genotype, OR ¼ 0:67, 95% CI ¼ 0:29–1:55) and non-14 carriers (TM genotype, OR ¼ 1:14, 95% CI ¼ 0:67–1:95; MM genotype, OR ¼ 1:15, 95% CI ¼ 0:63–2:09). Our analysis showed the expected association between the APOE 14 alele and AD with an OR of 4.61 (95% CI ¼ 3:14–6:76, P , 0:0001) for carrying one copy of 14, and an OR of 24.32 (95% CI ¼ 6:28–1, P , 0:0001) for carrying two copies of 14. We then examined the influence of T174M PRND genotypes on the age at onset of AD, and no significant variation existed among TT (mean age of 73.3, SD 6.9 years), TM (mean age of 71.2, SD 9.2 years), and MM (mean age of 72.8, SD 9.0 years) genotypes. The present study failed to replicate the findings of Schro¨ der et al. [14], and there were no significant differences in the percentage of patients with AD and controls with the T174M PRND M-carrying genotype (TM and MM genotypes), even after stratifying by age, sex, and APOE carrier status. The previous positive results of Schro¨ der et al. may have arisen by chance due to the very small sample size of sporadic AD cases studied. In the present report we have employed larger numbers of patients and controls compared to that previous study. Alternatively, an interpretation of this discrepancy would be an ethnic difference in AD susceptibility associated with the T174M PRND polymorphism. In fact, it is noteworthy that the difference in M allele frequency in controls produced in our study (51%) is large when compared to the frequency reported by Schro¨ der in a German population (37%). Our data for the M allele frequency in controls concurs with two independent reports in Great Britain (52%) [8] and France (49%) [11], that did not find any association between this polymorphism and CJD. Therefore, the association found in the German AD population might be due to a linkage disequilibrium between the PRND and other susceptibility gene located nearby, and not present in our Spanish patients. Our negative results with PRND polymorphism together with our previously reported failure to detect a significant association between 129 PRNP polymorphism and AD [4], indicates that the prion gene complex comprising PRNP and PRND is not a major locus conferring susceptibility to sporadic AD in the Spanish population. [1] Alperovitch, A., Zerr, I., Pocchiari, M., Mitrova, E., dePedroCuesta, J., Hegyi, I., Collins, S., Kretzschmar, H., vanDuijn, C. and Will, R.G., Codon 129 prion protein genotype and sporadic Creutzfeldt–Jakob disease, Lancet, 353 (1999) 1673–1674.
215
[2] Behrens, A. and Aguzzi, A., Small is not beautiful: antagonizing functions for the prion protein PrP c and its homologue Dpl, Trends Neurosci., 25 (2002) 150–154. [3] Casadei, V.M., Ferri, C., Calabrese, E., Franceschi, M., Veglia, F., Licastro, F., Mariani, C. and Grimaldi, L.M.E., Prion protein gene polymorphism and Alzheimer’s disease: one modulatory trait of cognitive decline? J. Neurol. Neurosurg. Psychiatry, 71 (2001) 279–280. [4] Combarros, O., Sa´ nchez-Guerra, M., Llorca, J., AlvarezArcaya, A., Berciano, J., Pen˜ a, N. and Ferna´ ndez-Viadero, C., Polymorphism at codon 129 of the prion protein gene is not associated with sporadic AD, Neurology, 55 (2000) 593– 595. [5] Ellis, R.J. and Pinheiro, T.J.T., Danger - misfolding proteins, Nature, 416 (2002) 483–484. [6] Mastrangelo, P. and Westaway, D., The prion gene complex encoding PrP c and Doppel: insights from mutational analysis, Gene, 275 (2001) 1–18. [7] McKhaan, G., Drachman, D., Folstein, M., Katzman, R., Price, D. and Stadlan, E.M., Clinical diagnosis of Alzheimer’s disease: report of the NINCDA-ADRDA Work Group under the auspices of Department of Health and Human Services Task Force on Alzheimer’s Disease, Neurology, 34 (1984) 934–944. [8] Mead, S., Beck, J., Dickinson, A., Fisher, E.M.C. and Collinge, J., Examination of the human prion protein-like gene Doppel for genetic susceptibility to sporadic and variant Creutzfeldt–Jakob disease, Neurosci. Lett., 290 (2000) 117–120. [9] Mo, H., Moore, R.C., Cohen, F.E., Westaway, D., Prusiner, S.B., Wright, P.E. and Dyson, H.J., Two different neurodegenerative diseases caused by proteins with similar structures, Proc. Natl. Acad. Sci. USA, 98 (2001) 2352–2357. [10] Palmer, M.S., Dryden, A.J., Hughes, J.T. and Collinge, J., Homozygous prion protein genotype predisposes to sporadic Creutzfeldt–Jakob disease, Nature, 352 (1991) 340–342. [11] Peoch, K., Gue´ rin, C., Brandel, J.P., Launay, J.M. and Laplanche, J.L., First report of polymorphisms in the prion-like protein gene (PRND): implications for human prion diseases, Neurosci. Lett., 286 (2000) 144–148. [12] Prusiner, S.B., Prions, Proc. Natl. Acad. Sci. USA, 95 (1998) 13363–13383. [13] Rossi, D., Cozzio, A., Flechsig, E., Klein, M.A., Ru¨ licke, T., Aguzzi, A. and Weissmann, C., Onset of ataxia and Purkinje cell loss in PrP null mice inversely correlated with Dpl level in brain, EMBO J., 20 (2001) 694–702. [14] Schro¨ der, B., Franz, B., Hempfling, P., Selbert, M., Ju¨ rgens, T., Kretzschmar, H.A., Bodemer, M., Poser, S. and Zerr, I., Polymorphisms within the prion-like protein gene (Prnd) and their implications in human prion diseases: Alzheimer’s disease and other neurological disorders, Hum. Genet., 109 (2001) 319–325. [15] Welch, W.J. and Gambetti, P., Chaperoning brain diseases, Nature, 392 (1998) 23–24. [16] Westaway, D. and Carlson, G.A., Mammalian prion proteins: enigma, variation and vaccination, Trends Biochem. Sci., 27 (2002) 301–307. [17] Windl, O., Dempster, M., Estibeiro, J.P., Lathe, R., de Silva, R., Esmonde, T., Will, R., Springbett, A., Campbell, T.A., Sidle, K.C.L., Palmer, M.S. and Collinge, J., Genetic basis of Creutzfeldt–Jakob disease in the United Kingdom: a systematic analysis of predisposing mutations and allelic variation in the PRNP gene, Hum. Genet., 98 (1996) 259–264.