Adults with Down syndrome in randomized clinical trials targeting prevention of Alzheimer's disease.

INTRODUCTION: Adults with Down syndrome, the largest population genetically predisposed to high risk for Alzheimer's disease (AD), are ideally suited participants for clinical trials targeting prevention. Critically important considerations for the design of such trials include appropriate selection of participants, outcome measures, and duration of follow-up. METHODS: Archived data for 12 measures of performance over a 3-year period were analyzed for 185 adults with Down syndrome 36 years of age and older with presumptive preclinical AD. RESULTS: Declines over 3 years were not observed prior to 46 years of age. However, declines were observed at older ages, increasing monotonically for groups aged 46-49, 50-55, and >55, as did incidence of prodromal AD and dementia. DISCUSSION: Significant decline over a 2- to 3-year period for a prospective placebo group of adults with Down syndrome enrolled in clinical prevention trials can only be expected when inclusion is limited to adults older than 45 years of age.

Longitudinal telomere shortening and early Alzheimer's disease progression in adults with down syndrome.

Telomere shortening was shown to parallel Alzheimer's disease (AD) associated dementia. By using a dual PNA Probe system we have developed a practical method for comparing telomere length in T-lymphocyte interphases from individuals with Down syndrome (DS) with and without "mild cognitive impairment" (MCI-DS) and demonstrated that telomere length can serve as a valid biomarker for the onset of MCI-DS in this high-risk population. To verify progressive cognitive decline we have now examined sequential changes in telomere length in 10 adults with DS (N = 4 Female, N = 6 Male) developing MCI-DS. Cases were selected blind to telomere length from a sample of adults with DS previously enrolled in a prospective longitudinal study at 18-month intervals with clinical and telomere assessments: (1) MCI-DS group data were collected approximately three years prior to development of MCI-DS; (2) 18 months later; (3) when MCI-DS was first observed. These telomere measures were compared to those from another 10 adults with DS matched by sex and approximate age but without indications of MCI-DS (Controls). PNA (peptide nucleic acid) probes for telomeres together with a chromosome two centromere probe were used. Findings indicated telomere shortening over time for both Cases and Controls. Group differences emerged by 18-months prior to recognition of MCI-DS onset and completely non-overlapping distributions of telomere measures were observed by the time of MCI-DS onset. This study adds to accumulating evidence of the value of telomere length, as an early biomarker of AD progression in adults with Down syndrome.

Telomere longitudinal shortening as a biomarker for dementia status of adults with Down syndrome.

Previous studies have suggested that Alzheimer's disease (AD) causes an accelerated shortening of telomeres, the ends of chromosomes consisting of highly conserved TTAGGG repeats that, because of unidirectional 5'-3' DNA synthesis, lose end point material with each cell division. Our own previous work suggested that telomere length of T-lymphocytes might be a remarkably accurate biomarker for "mild cognitive impairment" in adults with Down syndrome (MCI-DS), a population at dramatically high risk for AD. To verify that the progression of cognitive and functional losses due to AD produced this observed telomere shortening, we have now examined sequential changes in telomere length in five individuals with Down syndrome (3F, 2M) as they transitioned from preclinical AD to MCI-DS (N = 4) or dementia (N = 1). As in our previous studies, we used PNA (peptide nucleic acid) probes for telomeres and the chromosome 2 centromere (as an "internal standard" expected to be unaffected by aging or dementia status), with samples from the same individuals now collected prior to and following development of MCI-DS or dementia. Consistent shortening of telomere length was observed over time. Further comparisons with our previous cross-sectional findings indicated that telomere lengths prior to clinical decline were similar to those of other adults with Down syndrome (DS) who have not experienced clinical decline while telomere lengths following transition to MCI-DS or dementia in the current study were comparable to those of other adults with DS who have developed MCI-DS or dementia. Taken together, findings indicate that telomere length has significant promise as a biomarker of clinical progression of AD for adults with DS, and further longitudinal studies of a larger sample of individuals with DS are clearly warranted to validate these findings and determine if and how factors affecting AD risk also influence these measures of telomere length.

Prodromal Alzheimer's disease can affect activities of daily living for adults with Down syndrome.

INTRODUCTION: Alzheimer's disease (AD) affecting adults with Down syndrome (DS-AD), like late-onset AD (LOAD) in the neurotypical population, has preclinical, prodromal, and more advanced stages. Only tasks placing high demands on cognition are expected to be affected during the prodromal stage, with activities of daily living (ADLs) typically being spared. However, cognitive demands of ADLs could be high for adults with DS and may be affected during prodromal DS-AD. METHODS: Cognitively stable cases that subsequently developed prodromal DS-AD were identified within a set of archived data from a previous longitudinal study. Measures of ADLs and multiple cognitive domains were examined over time. RESULTS: Clear declines in ADLs accompanied cognitive declines with prodromal DS-AD while stability in all measures was verified during preclinical DS-AD. DISCUSSION: Operationally defining prodromal DS-AD is essential to disease staging in this high-risk population and for informing treatment options and timing as new disease-modifying drugs become available. Highlights: Cognitive and functional stability were demonstrated prior to the onset of prodromal DS-AD.ADL declines accompanied cognitive declines as adults with DS transitioned to prodromal AD.Declines in ADLs should be a defining feature of prodromal AD for adults with DS.Better characterization of prodromal DS-AD can improve AD diagnosis and disease staging.Improvements in DS-AD diagnosis and staging could also inform the timing of interventions.

Altered DNA methylation in leukocytes with trisomy 21.

The primary abnormality in Down syndrome (DS), trisomy 21, is well known; but how this chromosomal gain produces the complex DS phenotype, including immune system defects, is not well understood. We profiled DNA methylation in total peripheral blood leukocytes (PBL) and T-lymphocytes from adults with DS and normal controls and found gene-specific abnormalities of CpG methylation in DS, with many of the differentially methylated genes having known or predicted roles in lymphocyte development and function. Validation of the microarray data by bisulfite sequencing and methylation-sensitive Pyrosequencing (MS-Pyroseq) confirmed strong differences in methylation (p<0.0001) for each of 8 genes tested: TMEM131, TCF7, CD3Z/CD247, SH3BP2, EIF4E, PLD6, SUMO3, and CPT1B, in DS versus control PBL. In addition, we validated differential methylation of NOD2/CARD15 by bisulfite sequencing in DS versus control T-cells. The differentially methylated genes were found on various autosomes, with no enrichment on chromosome 21. Differences in methylation were generally stable in a given individual, remained significant after adjusting for age, and were not due to altered cell counts. Some but not all of the differentially methylated genes showed different mean mRNA expression in DS versus control PBL; and the altered expression of 5 of these genes, TMEM131, TCF7, CD3Z, NOD2, and NPDC1, was recapitulated by exposing normal lymphocytes to the demethylating drug 5-aza-2'deoxycytidine (5aza-dC) plus mitogens. We conclude that altered gene-specific DNA methylation is a recurrent and functionally relevant downstream response to trisomy 21 in human cells.

Individualized estimated years from onset of Alzheimer's disease- related decline for adults with Down syndrome.

Introduction: Adults with Down syndrome (DS) are at increased risk for Alzheimer's disease (AD) and vary in their age of transition from AD preclinical to prodromal or more advanced clinical stages. An empirically based method is needed to determine individual "estimated years from symptom onset (EYO)," the same construct used in studies of autosomal dominant AD . Methods: Archived data from a previous study of > 600 adults with DS were examined using survival analysis methods. Age-specific prevalence of prodromal AD or dementia, cumulative risk, and EYOs were determined. Results: Individualized EYOs for adults with DS ranging in age from 30 to 70+ were determined, dependent upon chronological age and clinical status. Discussion: EYOs can be a useful tool for studies focused on biomarker changes during AD progression in this and other populations at risk, studies that should contribute to improved methods for diagnosis, prediction of risk, and identification of promising treatment targets. HIGHLIGHTS: Years from Alzheimer's disease (AD) onset (EYO) was estimated for adults with Down syndrome (DS).EYOs were informed by AD clinical status and age, ranging from 30 to > 70 years.Influences of biological sex and apolipoprotein E genotype on EYOs were examined.EYOs have advantages for predicting risk of AD-related dementia compared to age.EYOs can be extremely informative in studies of preclinical AD progression.

Mild cognitive impairment identified in older individuals with Down syndrome by reduced telomere signal numbers and shorter telomeres measured in microns.

Previously, we established that short-term T lymphocyte cultures from people with Down syndrome (DS) and dementia (Alzheimer's disease) had shorter telomeres than did those from age- and sex-matched people with DS only, quantified as significantly reduced numbers of signals of peptide nucleic acid (PNA) telomere probes in whole metaphases [Jenkins et al. (2008); Neurosci Lett 440:340-343] as well as reduced telomere probe light intensity values in interphases [Jenkins et al. (2010); Neurobiol Aging 31:765-771]. We now describe shorter telomere length in adults with DS and mild cognitive impairment (MCI) compared to age- and sex-matched individuals with DS without MCI. Telomere length is quantified by reduced telomere signal numbers and shorter chromosome 1 telomeres measured in micrometers (microns). These findings were in agreement with quantitative light intensity measurements of chromosome 1 and chromosome 21 PNA telomere probes with and without the use of a "normalizing ratio" involving the fluorescence exhibited by a PNA probe for centromere 2, and with the use of light intensity measurements of interphase preparations. Most importantly, the distributions of chromosome 1 telomere lengths (in microns) were completely non-overlapping for adults with and without MCI, indicating that this measure has great promise as a biomarker for MCI as well as dementia in this population.

Estrogen receptor-Beta variants are associated with increased risk of Alzheimer's disease in women with down syndrome.

BACKGROUND/AIMS: Genetic variants that affect estrogen activity may influence the risk of Alzheimer's disease (AD). We examined the relation of polymorphisms in the gene for the estrogen receptor-beta (ESR2) to the risk of AD in women with Down syndrome. METHODS: Two hundred and forty-nine women with Down syndrome, 31-70 years of age and nondemented at baseline, were followed at 14- to 18-month intervals for 4 years. Women were genotyped for 13 single-nucleotide polymorphisms (SNPs) in the ESR2 gene, and their association with AD incidence was examined. RESULTS: Among postmenopausal women, we found a 2-fold increase in the risk of AD for women carrying 1 or 2 copies of the minor allele at 3 SNPs in introns seven (rs17766755) and six (rs4365213 and rs12435857) and 1 SNP in intron eight (rs4986938) of ESR2. CONCLUSION: These findings support a role for estrogen and its major brain receptors in modulating susceptibility to AD in women.

The Association between Sex and Risk of Alzheimer's Disease in Adults with Down Syndrome.

BACKGROUND: Sex differences in the risk of Alzheimer's Disease (AD) in adults with Down Syndrome (DS) have not been extensively investigated, and existing studies have found conflicting results. This study examined the effect of sex on the risk of AD in adults with DS, adjusted for covariates. METHODS: Adults with DS were assessed longitudinally for the development of AD. Competing risk survival analyses were used to determine the effect of sex alone and after adjustment for APOE-ε4 status, ethnicity, and level of intellectual disability (ID). RESULTS: Sex differences were significant only in adults over 60 years of age, where men with DS were 6.32 (95% CI: 2.11-18.96, p < 0.001) times more likely to develop AD compared with age-matched women with DS. CONCLUSIONS: There is an age-associated effect of sex on the risk of AD, with men over 60 years old having six times the risk of AD compared with age-matched women, independent of APOE-ε4 status, ethnicity, and level of ID.

Promising outcome measures of early Alzheimer's dementia in adults with Down syndrome.

INTRODUCTION: Adults with Down syndrome (DS) are at high risk for developing Alzheimer's disease (AD) and its associated dementia, warranting the development of strategies to improve early detection when prevention is possible. METHODS: Using a broad battery of neuropsychological assessments, informant interviews, and clinical record review, we evaluated the psychometrics of measures in a large sample of 561 adults with DS. We tracked longitudinal stability or decline in functioning in a subsample of 269 participants over a period of 3 years, all initially without indications of clinically significant aging-related decline. RESULTS: Results identified an array of objective measures that demonstrated sensitivity in distinguishing individuals with incident "mild cognitive impairment" (MCI-DS) as well as subsequent declines occurring with incident dementia. DISCUSSION: Several instruments showed clear promise for use as outcome measures for future clinical trials and for informing diagnosis of individuals suspected of experiencing early signs and symptoms of a progressive dementia process.

Increased "absence" of telomeres may indicate Alzheimer's disease/dementia status in older individuals with Down syndrome.

We have reported previously that telomeres (ends of chromosomes consisting of highly conserved TTAGGG repeats) were shorter in metaphase and interphase preparations in T lymphocytes from short-term whole blood cultures of women with Down syndrome (DS) and dementia compared to age-matched women with DS but without dementia [E.C. Jenkins, M.T. Velinov, L. Ye, H. Gu, S. Li, E.C. Jenkins Jr., S.S. Brooks, D. Pang, D.A. Devenny, W.B. Zigman, N. Schupf, W.P. Silverman, Telomere shortening in T lymphocytes of older individuals with Down syndrome and dementia, Neurobiol. Aging 27 (2006) 41-45]. Our previous study was carried out by measuring changes in fluorescence intensity [using an FITC-labeled peptide nucleic acid (PNA) probe (Applied Biosystems; DAKO) and Applied Imaging software], and we now report on a substantially simpler metric, counts of signals at the ends of chromosomes. Nine adults with DS and dementia plus four who are exhibiting declines in cognition analogous to mild cognitive impairment in the general population (MCI-DS) were compared to their pair-matched peers with DS but without dementia or MCI-DS. Results indicated that the number of chromosome ends that failed to exhibit fluorescent signal from the PNA telomere probe was higher for people with dementia or mild cognitive impairment (MCI-DS). Thus, a simple count of chromosome ends for the "presence/absence" of fluorescence may provide a valid biomarker of dementia status. If this is the case, then after additional research for validation to assure high specificity and sensitivity, the test may be used to identify and ultimately guide treatment for people at increased risk for developing mild cognitive impairment and/or dementia.

Estrogen receptor-alpha variants increase risk of Alzheimer's disease in women with Down syndrome.

BACKGROUND: Genetic variants that affect estrogen activity may influence the risk of Alzheimer's disease (AD). Two tightly linked polymorphisms (PvuII and XbaI) in the first intron of estrogen receptor 1 (ESR1), the gene for ER-alpha, have been reported to influence estrogen receptor expression and may influence the risk of AD. METHODS: We examined the relation of polymorphisms in ESR1 to the risk of AD in women with Down syndrome. The subjects (181 women with DS, 41-78 years of age) were followed at 14- to 18-month intervals. Information from cognitive assessments, caregiver interviews, medical record reviews and neurological examinations was used to classify dementia. Genomic DNA was genotyped for 5 single-nucleotide polymorphisms in the upstream region and the first exon/intron of the ESR1 gene. Their association with dementia risk was evaluated, adjusting for covariates. RESULTS: Women with at least 1 copy of the C allele at rs2234693 (PvuII) and those homozygous for the C allele at rs2077647 had an almost 3-fold increase in the risk of AD, compared with women without the C allele. The increased risks were independent of the apolipoprotein E genotype. CONCLUSION: These findings support a role for estrogen receptor activity in the development of AD in women with Down syndrome.

Maladaptive behaviors related to dementia status in adults with Down syndrome.

Changes in maladaptive behaviors related to specific stages of dementia were investigated in 251 adults 45 years of age and older with Down syndrome. Findings indicate clear differences in maladaptive behaviors at various stages of dementia. Generally, individuals with no signs or symptoms of dementia displayed fewer and less severe maladaptive behaviors than individuals in the early and mid-stages of dementia. Individuals transitioning into the early stages of dementia from no dementia displayed increased aggression, fearfulness, sadness, sleep problems, social inadequacy, stealing, and general regressive behavior. Thus, new concerns regarding these types of behaviors could be particularly useful in clarifying the dementia status of adults with Down syndrome and developing individualized plans for support.

Epidemiology of estrogen and dementia in women with Down syndrome.

Several lines of investigation have shown a protective role for estrogen in Alzheimer's disease through a number of biological actions. This review examines studies of the role of estrogen-related factors in age at onset and risk for Alzheimer's disease in women with Down syndrome, a population at high risk for early onset of dementia. The studies are consistent in showing that early age at menopause and that low levels of endogenous bioavailable estradiol in postmenopausal women with Down syndrome are associated with earlier age at onset and overall risk for dementia. Polymorphisms in genes associated with estrogen receptor activity and in genes for estrogen biosynthesis affecting endogenous estrogen are related to age at onset and cumulative incidence of dementia, and may serve as biomarkers of risk. To date, no clinical trials of estrogen or hormone replacement therapy (ERT/HRT) have been published for women with Down syndrome. While findings from clinical trials of ERT or HRT for dementia have generally been negative among women in the neurotypical population, the short interval between menopause and onset of cognitive decline, together with a more positive balance between potential benefits and risks, suggests an opportunity to evaluate the efficacy of ERT/HRT for delaying or preventing dementia in this high risk population, although questions concerning the optimal formulation and timing of the hormone therapy are not yet resolved.

Elevated plasma beta-amyloid peptide Abeta(42) levels, incident dementia, and mortality in Down syndrome.

BACKGROUND: Deposition of the beta-amyloid peptide Abeta(42) is thought to be an important initial step in the pathogenesis of Alzheimer disease (AD). Individuals with Down syndrome have increased levels of beta-amyloid peptides and an increased risk for AD. OBJECTIVE: To examine the relation of plasma levels of Abeta(42) and Abeta(40) to the risk of dementia in nondemented participants and all-cause mortality in adults with Down syndrome. DESIGN: Prospective, community-based longitudinal cohort study. SETTING: State and voluntary service providers in New York State. PARTICIPANTS: Adults with Down syndrome (N = 204). MAIN OUTCOME MEASURE: Plasma Abeta(42) and Abeta(40) levels were measured at initial examination. Participants were assessed for cognitive and functional abilities, behavioral/psychiatric conditions, and health and vital status at 14- to 18-month intervals for 4 cycles of data collection. RESULTS: Among participants who were nondemented at baseline, those in the middle and highest tertiles of plasma Abeta(42) levels were more than 2 times as likely to develop AD as those in the lowest tertile. Compared with participants without AD, participants with prevalent AD had higher levels of plasma Abeta(42) but not Abeta(40). Among all participants, those in the highest tertile of plasma Abeta(42) level at baseline were more than twice as likely to die during the study period as those in the lowest tertile, whereas there was no difference in risk of death between those in the middle and lowest tertiles of plasma Abeta(42) level. CONCLUSION: Elevations in plasma Abeta(42) peptide levels are associated with earlier onset of AD and increased risk of death.

Association between genetic variants in sortilin-related receptor 1 (SORL1) and Alzheimer's disease in adults with Down syndrome.

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.

Cholesterol level, statin use and Alzheimer's disease in adults with Down syndrome.

Adults with Down syndrome (DS) are at significantly higher risk of Alzheimer's disease (AD) than the general population, but there is considerable variability in age at onset. This study tested the hypothesis that total cholesterol (TC) levels are related to vulnerability, and that the use of statins may decrease risk. The relation of TC level and statin use to risk of AD was investigated in 123 Caucasian adults with DS. Evaluations included serial assessments of cognitive, adaptive and maladaptive behavior, medical records, and neurological examinations. Mean length of follow-up was 5.5 years [1.2-7.1] for the entire sample, 5.1 years [1.2-7.1] for subjects who developed dementia, and 5.6 years [1.5-7.1] for those who did not develop dementia. Controlling for covariates, participants with TC>or=200mg/dL were more than two times as likely to develop AD than subjects with lower TC [hazard rate (HR)=2.59, p=.029, 95% CI: 1.1, 6.1]. In contrast, participants with higher TC levels who used statins during the study, had less than half the risk of developing AD than participants with higher TC levels who did not use statins (HR=.402, p=.095, 95% CI: .138, 1.173). If the protective effects of statins can be further validated, these findings suggest that their use may delay or prevent AD onset in vulnerable populations.

Candidate gene analysis for Alzheimer's disease in adults with Down syndrome.

Individuals with Down syndrome (DS) overexpress many genes on chromosome 21 due to trisomy and have high risk of dementia due to the Alzheimer's disease (AD) neuropathology. However, there is a wide range of phenotypic differences (e.g., age at onset of AD, amyloid ß levels) among adults with DS, suggesting the importance of factors that modify risk within this particularly vulnerable population, including genotypic variability. Previous genetic studies in the general population have identified multiple genes that are associated with AD. This study examined the contribution of polymorphisms in these genes to the risk of AD in adults with DS ranging from 30 to 78 years of age at study entry (N = 320). We used multiple logistic regressions to estimate the likelihood of AD using single-nucleotide polymorphisms (SNPs) in candidate genes, adjusting for age, sex, race/ethnicity, level of intellectual disability and APOE genotype. This study identified multiple SNPs in APP and CST3 that were associated with AD at a gene-wise level empirical p-value of 0.05, with odds ratios in the range of 1.5-2. SNPs in MARK4 were marginally associated with AD. CST3 and MARK4 may contribute to our understanding of potential mechanisms where CST3 may contribute to the amyloid pathway by inhibiting plaque formation, and MARK4 may contribute to the regulation of the transition between stable and dynamic microtubules.

Telomere shortening in T lymphocytes of older individuals with Down syndrome and dementia.

Telomere shortening has been recently correlated with Alzheimer's disease status. Therefore, we hypothesized that a possible association might exist for adults with Down syndrome (DS). Using blind, quantitative telomere protein nucleic acid FISH analyses of metaphase and interphase preparations from 18 age-matched trisomy 21 female study participants with and without dementia, we have observed increased telomere shortening in adults with DS and dementia (p < .01). From this initial study, we conclude that telomere shortening is associated with dementia in this high-risk population and suggest that additional research may show that telomere shortening may be a biological marker of dementia status.

Cell type-specific over-expression of chromosome 21 genes in fibroblasts and fetal hearts with trisomy 21.

BACKGROUND: Down syndrome (DS) is caused by trisomy 21 (+21), but the aberrations in gene expression resulting from this chromosomal aneuploidy are not yet completely understood. METHODS: We used oligonucleotide microarrays to survey mRNA expression in early- and late-passage control and +21 fibroblasts and mid-gestation fetal hearts. We supplemented this analysis with northern blotting, western blotting, real-time RT-PCR, and immunohistochemistry. RESULTS: We found chromosome 21 genes consistently over-represented among the genes over-expressed in the +21 samples. However, these sets of over-expressed genes differed across the three cell/tissue types. The chromosome 21 gene MX1 was strongly over-expressed (mean 16-fold) in senescent +21 fibroblasts, a result verified by northern and western blotting. MX1 is an interferon target gene, and its mRNA was induced by interferons present in +21 fibroblast conditioned medium, suggesting an autocrine loop for its over-expression. By immunohistochemistry the p78MX1 protein was induced in lesional tissue of alopecia areata, an autoimmune disorder associated with DS. We found strong over-expression of the purine biosynthesis gene GART (mean 3-fold) in fetal hearts with +21 and verified this result by northern blotting and real-time RT-PCR. CONCLUSION: Different subsets of chromosome 21 genes are over-expressed in different cell types with +21, and for some genes this over-expression is non-linear (>1.5X). Hyperactive interferon signaling is a candidate pathway for cell senescence and autoimmune disorders in DS, and abnormal purine metabolism should be investigated for a potential role in cardiac defects.