title: Association between genetic variants in sortilin-related receptor 1 (SORL1) and Alzheimer's disease in adults with Down syndrome.
abstract: Recent reports have suggested that variants in the sortilin-related receptor gene (SORL1) increase the risk of late onset Alzheimer's disease (AD) in Northern European, Hispanic, African-American and Isreali-Arab populations. SORL1 directs trafficking of amyloid precursor protein (APP) and under-expression of SORL1 may lead to over-expression of beta amyloid peptides. Adults with Down syndrome (DS) over-express APP and have early onset and high risk for AD. We investigated the relation of seven variants in the gene for SORL1 to age at onset and risk for AD among 208 adults with DS, 45-70 years of age at baseline. Participants were ascertained through the New York State developmental disability service system and followed at 18-month intervals. Information from cognitive assessments, caregiver interviews, medical record review and neurological examination was used to establish the diagnosis of dementia. Homozygosity for the minor T allele in rs556349 and for the minor C allele in rs536360 was associated with later age at onset and reduced risk of AD (HR=0.26, 95% CI: 0.08-0.86; and HR=0.40, 95% CI: 0.16-0.98, respectively). Mean age at onset was approximately four years later in individuals who were homozygous for those alleles compared with those who had at least one major allele. These findings indicate a modest association of variants in SORL1 with AD. In addition, we did not observe the same alleles to be associated with AD compared with earlier studies, suggesting that these SNPs are in linkage disequilibrium (LD) with the putative functional variants or that expression of the SORL1 gene and hence its interaction with APP might be modified by the extremely high levels of APP characteristic of Down syndrome. Thus, further studies are needed to identify functional variants that influence risk for AD in this uniquely vulnerable population.
authors.affiliation: The Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York, NY, USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Lee
authors.forename: Maruit
authors.initials: M
authors.lastname: Chulikavit
authors.forename: Deborah
authors.initials: D
authors.lastname: Pang
authors.forename: Warren B
authors.initials: WB
authors.lastname: Zigman
authors.forename: Wayne
authors.initials: W
authors.lastname: Silverman
authors.forename: Nicole
authors.initials: N
authors.lastname: Schupf
mesh_terms: D017668:Age of Onset; D000544:Alzheimer Disease / Q000453:epidemiology / Q000235:genetics*; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism; D001921:Brain / Q000378:metabolism / Q000503:physiopathology; D001923:Brain Chemistry / Q000235:genetics*; D015897:Comorbidity; D004252:DNA Mutational Analysis; D004314:Down Syndrome / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D005787:Gene Frequency / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D005820:Genetic Testing; D014644:Genetic Variation / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D026502:LDL-Receptor Related Proteins / Q000235:genetics*; D015810:Linkage Disequilibrium / Q000235:genetics; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics*; D008875:Middle Aged; D009483:Neuropsychological Tests; D012307:Risk Factors