Genetic variants within two distinct regions of SORL1 have recently been associated with both familial and sporadic Alzheimer's disease (AD) in multiple cohorts composed of more than 6,000 individuals (1). The original report was subsequently confirmed in an independent cohort of unrelated patients with probable AD and healthy elderly controls from a prospective study in multiethnic communities in northern Manhattan (2). To extend these results, we investigated a series of autopsy confirmed cases with AD (n=103) of white, non-Hispanic origin, and compared them to controls (n = 93) from similar ethnic origins. These analyses revealed that the same alleles in a haplotype in the 5’ region of the gene and a haplotype in the same 3’ region are associated with autopsy proven AD.
Frozen brain tissue was obtained from 103 autopsy confirmed cases of AD, and from 17 elderly controls with a normal postmortem examination, and without a history of dementia or another neurological disorder. . To augment the number of controls from the same ethnic background, we included 76 non-demented elderly participants who have been followed prospectively at approximately 18-month intervals as part of a study of aging and dementia among Medicare recipients residing in northern Manhattan since 1999 (3-5). The average age of onset for the patients was 80.5 and 52.4% were women. The mean age of the combined group of controls was 79.7 years and 48.4% were women. The Institutional Review Boards of Columbia University Medical Center and the New York Psychiatric Institute approved recruitment, informed consent and study procedures.
Genotyping was performed using matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (Sequenom). Detailed information on genotyping was previously described (1), and is available upon request. The numbering system for the SNPs 1 to 29 reflects their relative order on the physical map of SORL1, and was the same system used in the previous publication (1). We restricted the work to include only 12 of the previously genotyped SNPs to focus on 5’ (SNPs 1, 2 and 7−10) and 3’ (SNPs 13, 17 and 22−25) regions highlighted in the previous report. SNP marker data were assessed for deviations from Hardy-Weinberg equilibrium using the HAPLOVIEW program (6), and none deviated. The χ2 test (or the Fisher's exact test) was used to for analysis of genotypic and allelic associations between AD and each of the SNP markers. The HAPLOVIEW program was used to perform single point analysis, estimates of linkage disequilibrium (LD) structure and haplotype blocks. Haplotype analyses were performed with HAPLO.STATS v1.1.1 for case-control data using the same sliding window of three contiguous SNPs as described in our previous publication (1). The objective of this study was to confirm associations in the previous two studies (1, 2), therefore a nominal p-value of 0.05 wass considered sufficient evidence of confirmation (7). Consequently, nominal p-values are presented in the table for single point and haplotype analyses.
The single SNP analyses revealed that the C and G alleles in SNPs 8 and 9 were significantly associated with AD (0.015 ≤ p ≤ 0.017, table 1a). Haplotype analysis confirmed this result, showing that the CGC haplotype in SNPs 8−9−10 was also significantly associated with AD (nominal p=0.0047, global p = 0.02, table 1b). Importantly, these were the same alleles within the same haplotype that was associated with AD in Caribbean Hispanic families, the Israeli Arabs and the northern European case-control series in the initial report(1). Haplotypes in the 3’ region involving SNPs 23−24−25 previously found to be associated with AD were also statistically significant (nominal p=0.015, global p =0.012, table 1b), but the alleles differed; ATC in the current report contrasted with TTC in the original report (1).
Table 1a and 1b.
Results of genotyping of the 12 SNPs in SORL1 by single point and haplotype analysis. The SNP order refers to original order of the SNPs in our previous publication (1). The single SNPs and haplotypes in boldface were statistically significant. The associated alleles for SNPs 8 and 9 were identical to those in the original manuscript as was the haplotype CGC from SNPs 8−9−10 (1).
| 1a. SORL1 SNP Order (1) | SNP Name | Associated Allele | Frequency Cases : Controls | X2 | P-value | ||
|---|---|---|---|---|---|---|---|
| 1 | rs4935774 | A | 0.789 : 0.703 | 2.793 | 0.0947 | ||
| 2 | rs578506 | C | 0.531 : 0.451 | 1.843 | 0.1746 | ||
| 7 | rs12364988 | G | 0.588 : 0.506 | 2.106 | 0.1467 | ||
| 8 | rs668387 | C | 0.665 : 0.534 | 5.885 | 0.0153 | ||
| 9 | rs689021 | G | 0.654 : 0.518 | 5.655 | 0.0174 | ||
| 10 | rs641120 | C | 0.654 : 0.588 | 1.401 | 0.2365 | ||
| 13 | rs2298813 | A | 0.047 : 0.034 | 0.319 | 0.572 | ||
| 17 | rs556349 | T | 0.338 : 0.330 | 0.025 | 0.8733 | ||
| 22 | rs1699102 | C | 0.354 : 0.335 | 0.136 | 0.7123 | ||
| 23 | rs3824968 | A | 0.316 : 0.259 | 1.198 | 0.2736 | ||
| 24 | rs2282649 | T | 0.301 : 0.212 | 3.229 | 0.0724 | ||
| 25 | rs1010159 | T | 0.662 : 0.625 | 0.451 | 0.502 | ||
| 1b. Haplotype Location | Haplotype | Frequency Cases : Controls | Z score | Haplotype P-value | Global P-value | ||
|---|---|---|---|---|---|---|---|
| 8−9−10 | T | A | T | 0.334 : 0.432 | −1.8875 | 0.0591 | 0.02863 |
| C | A | C | 0.001 : 0.024 | −1.79354 | 0.0729 | ||
| T | G | C | 0.001 : 0.012 | −1.31871 | 0.1873 | ||
| T | A | C | 0.002 : 0.023 | −1.28693 | 0.1981 | ||
| C | G | C | 0.662 : 0.509 | 2.82608 | 0.0047 | ||
| 23−24−25 | T | C | C | 0.029 : 0.103 | −2.42463 | 0.0153 | 0.01255 |
| A | C | C | 0.007 : 0.052 | −2.11649 | 0.0343 | ||
| T | T | C | 0.009 : 0.013 | −1.37823 | 0.1681 | ||
| T | C | T | 0.654 : 0.628 | 0.49746 | 0.6189 | ||
| A | T | C | 0.301 : 0.204 | 2.00448 | 0.0450 | ||
These results provide yet further independent confirmation of the observation that inherited variants in SORL1 are associated with AD. Our findings in this series of white, non-Hispanic autopsy confirmed patients with AD and controls of European and North American ancestry are nearly identical to those in the original case control series of northern Europeans. As was apparent in the original and follow-up studies (1, 2), the significant association in two regions of the gene, and the discovery of different alleles within the AD-associated haplotypes in different datasets indicates that there may be a high degree of allelic heterogeneity, with disease-associated variants occurring on multiple different haplotype backgrounds. While the exact identity of the genetic effectors in SORL1 remains to be determined, it has been shown that SORL1 interacts with the amyloid precursor protein (APP), directs trafficking of APP into recycling pathways, and that when SORL1 is under-expressed, APP is sorted into Aβ-generating compartments (1, 8-11). Furthermore, neurons of in some patients with AD display low levels of SORL1, and knockout of SORL1 in mice has been associated with increased brain Aβ levels. The results reported here provide additional support for the association between genetic variants in SORL1 and AD in an independent series confirmed by postmortem examination.
Acknowledgments
This work was supported by grants from the National Institute of Health and the National Institute on Aging: P01-AG07232 and R37-AG15473 and P50-AG08702, the Alzheimer Association, the Blanchett Hooker Rockefeller Foundation, Charles S. Robertson Gift from the Banbury Fund (RM). The authors thank M. Wei, J. Kosek and B. Tycko for genotyping APOE and a subset of the SORL1 markers.
Footnotes
The authors have nothing to disclose.
References
- 1.Rogaeva E, Meng Y, Lee JH, et al. The neuronal sortilin-related receptor SORL1 is genetically associated with Alzheimer disease. Nat Genet. 2007;39:168–177. doi: 10.1038/ng1943. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Lee JH, Cheng R, Schupf N, et al. The association between genetic variants in SORL1 and Alzheimer disease in an urban, multiethnic, community-based cohort. Arch Neurol. 2007;64:501–506. doi: 10.1001/archneur.64.4.501. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Pittman J, Andrews H, Tatemichi T, et al. Diagnosis of dementia in a heterogeneous population. A comparison of paradigm-based diagnosis and physician's diagnosis. Arch Neurol. 1992;49:461–467. doi: 10.1001/archneur.1992.00530290043010. [DOI] [PubMed] [Google Scholar]
- 4.Stern Y, Andrews H, Pittman J, et al. Diagnosis of dementia in a heterogeneous population. Development of a neuropsychological paradigm-based diagnosis of dementia and quantified correction for the effects of education. Arch Neurol. 1992;49:453–460. doi: 10.1001/archneur.1992.00530290035009. [DOI] [PubMed] [Google Scholar]
- 5.Stricks L, Pittman J, Jacobs DM, Sano M, Stern Y. Normative data for a brief neuropsychological battery administered to English- and Spanish-speaking community-dwelling elders. J Int Neuropsychol Soc. 1998;4:311–318. [PubMed] [Google Scholar]
- 6.Barrett JC, Fry B, Maller J, Daly MJ. Haploview: analysis and visualization of LD and haplotype maps. Bioinformatics. 2005;21:263–265. doi: 10.1093/bioinformatics/bth457. [DOI] [PubMed] [Google Scholar]
- 7.Ott J. Analysis of human genetic linkage. 3rd ed. Johns Hopkins University Press; Baltimore: 1999. [Google Scholar]
- 8.Andersen OM, Reiche J, Schmidt V, et al. Neuronal sorting protein-related receptor sorLA/LR11 regulates processing of the amyloid precursor protein. Proc Natl Acad Sci U S A. 2005;102:13461–13466. doi: 10.1073/pnas.0503689102. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Andersen OM, Schmidt V, Spoelgen R, et al. Molecular dissection of the interaction between amyloid precursor protein and its neuronal trafficking receptor SorLA/LR11. Biochemistry. 2006;45:2618–2628. doi: 10.1021/bi052120v. [DOI] [PubMed] [Google Scholar]
- 10.Offe K, Dodson SE, Shoemaker JT, et al. The lipoprotein receptor LR11 regulates amyloid beta production and amyloid precursor protein traffic in endosomal compartments. J Neurosci. 2006;26:1596–1603. doi: 10.1523/JNEUROSCI.4946-05.2006. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Spoelgen R, von Arnim CA, Thomas AV, et al. Interaction of the cytosolic domains of sorLA/LR11 with the amyloid precursor protein (APP) and beta-secretase beta-site APP-cleaving enzyme. J Neurosci. 2006;26:418–428. doi: 10.1523/JNEUROSCI.3882-05.2006. [DOI] [PMC free article] [PubMed] [Google Scholar]