Shorter telomeres may indicate dementia status in older individuals with Down syndrome

We have recently reported reduced telomere length in T lymphocytes of individuals with Down syndrome (DS) and dementia due to Alzheimer's disease (AD). We have now replicated and extended that study by finding that people with DS and mild cognitive impairment (MCI-DS) also have shorter telomeres than people with DS without MCI-DS. Additional new findings demonstrated that light intensity measurements from chromosome 21 alone, or in concert with chromosomes 1, 2, and 16, exhibited shorter telomeres in adults with DS and with either dementia or MCI-DS compared to aging per se. Chromosome 21 measurements appeared to be especially promising for use as a biomarker because there was no overlap in the distribution of light intensity measurement scores between demented or MCI-DS and non-demented participants. Given that early clinical symptoms of AD can be very difficult to recognize in this population of adults due to their pre-existing cognitive impairments, a valid biomarker would be of great value. Early detection is especially important because it would allow treatments to begin before significant damage to the central nervous system has occurred. Our findings suggest that it may be feasible to use telomere shortening as a biomarker for accurately inferring dementia status.

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.

Successful aging in a 70-year-old man with down syndrome: a case study

The authors present a case study of a 70-year-old man with Down syndrome ("Mr. C.") who they followed for 16 years and who does not exhibit declines in cognitive or functional capacities indicative of dementia, despite having well-documented, complete trisomy 21. The authors describe the age-associated changes that occurred over 16 years as well as provide detailed information regarding Mr. C.'s health and genetic status. To further emphasize Mr. C.'s successful aging, the authors compared his longitudinal performance profile with that of 2 peers of comparable level of intellectual functioning: 1 similar-aged man with clinical Alzheimer's disease and a younger man who was healthy. The authors present potential explanations for the phenotypic variability observed in individuals with Down syndrome.

Alzheimer's disease in Down syndrome: neurobiology and risk

Down syndrome (DS) is characterized by increased mortality rates, both during early and later stages of life, and age-specific mortality risk remains higher in adults with DS compared with the overall population of people with mental retardation and with typically developing populations. Causes of increased mortality rates early in life are primarily due to the increased incidence of congenital heart disease and leukemia, while causes of higher mortality rates later in life may be due to a number of factors, two of which are an increased risk for Alzheimer's disease (AD) and an apparent tendency toward premature aging. In this article, we describe the increase in lifespan for people with DS that has occurred over the past 100 years, as well as advances in the understanding of the occurrence of AD in adults with DS. Aspects of the neurobiology of AD, including the role of amyloid, oxidative stress, Cu/ZN dismutase (SOD-1), as well as advances in neuroimaging are presented. The function of risk factors in the observed heterogeneity in the expression of AD dementia in adults with DS, as well as the need for sensitive and specific biomarkers of the clinical and pathological progressing of AD in adults with DS is considered.

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.

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.

Bioavailable estradiol and age at onset of Alzheimer's disease in postmenopausal women with Down syndrome

Several lines of evidence suggest that loss of estrogen after menopause may play a role in the cognitive declines associated with Alzheimer's disease (AD). Women with Down syndrome (DS) experience early onset of both menopause and AD. This timing provides a model to examine the influence of endogenous estrogen deficiency on risk of AD. We hypothesized that low serum levels of bioavailable estradiol (E2) would be associated with increased risk of AD. One hundred and nineteen postmenopausal women with DS, 42-59 years of age, 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. Women with DS who developed AD had lower levels of bioavailable E2, lower levels of total estradiol, higher levels of sex-hormone binding globulin, and lower levels of dehydroepiandrosterone sulfate at baseline than women who remained dementia free over the course of follow-up. Women who had low levels of bioavailable E2 at baseline were four times as likely to develop AD (HR=4.1, 95% CI: 1.2-13.9) and developed AD, on average, 3 years earlier, than those with high levels of bioavailable E2, after adjustment for age, level of mental retardation, ethnicity, body mass index, history of hypothyroidism or depression and the presence of the apolipoprotein varepsilon4 allele. Our findings support the hypothesis that reductions in estrogen following menopause can contribute to the cascade of pathological processes leading to AD.

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 p78^MX1 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.

Mortality is associated with apolipoprotein E ɛ4 in nondemented adults with Down syndrome

Apolipoprotein E genotype has been related to survival in the general population, but its strong association with Alzheimer's disease (AD) makes interpretation of findings difficult. Previous studies of adults with Down syndrome (DS) have consistently found that the presence of the apolipoprotein E epsilon2 allele increases longevity and reduces the risk of dementia, while the apolipoprotein E epsilon4 allele increases risk for dementia. In contrast, reduced frequencies of the apolipoprotein E epsilon4 allele among elderly groups have been reported, suggesting that the epsilon4 allele may be associated with early mortality in this population. To disentangle effects of dementia from those of aging, per se, we compared mortality risk as a function of apolipoprotein E genotype in 146 nondemented adults with DS in a prospective study. Individuals with at least one epsilon4 allele were approximately five times more likely to die within a 5- to 7-year follow-up period than those without an epsilon4 allele, adjusting for age, sex, body mass index, level of mental retardation, and cholesterol level. These results suggest that the apolipoprotein E epsilon4 allele has an independent and strong relation to early mortality.

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.

Incidence and prevalence of dementia in elderly adults with mental retardation without down syndrome

Rates of dementia in adults with mental retardation without Down syndrome were equivalent to or lower than would be expected compared to general population rates, whereas prevalence rates of other chronic health concerns varied as a function of condition. Given that individual differences in vulnerability to Alzheimer's disease have been hypothesized to be due to variation in cognitive reserve, adults with mental retardation, who have long-standing intellectual and cognitive impairments, should be at increased risk. This suggests that factors determining intelligence may have little or no direct relationship to risk for dementia and that dementia risk for individuals with mental retardation will be comparable to that of adults without mental retardation unless predisposing risk factors for dementia are also present.

Maladaptive behaviors related to adaptive decline in aging adults with mental retardation

Changes in patterns of maladaptive behavior related to age-associated adaptive declines were investigated in 529 adults with mental retardation. Although individuals with no significant adaptive decline displayed stable patterns of maladaptive behavior over a 3-year period, those with declines in function showed more variable patterns. Certain maladaptive behaviors were related to the onset of adaptive declines, with some becoming of increasing concern even before adaptive declines were noted (e.g., lack of boundaries). Other behaviors increased as adaptive declines developed (e.g., withdrawal). In general, findings suggest similarities in the course of age-associated dementia of adults with and without mental retardation and indicate that increases in selected areas of maladaptive behavior may be early indicators of concern for individuals at risk.

Incidence and temporal patterns of adaptive behavior change in adults with mental retardation

The age-associated incidence of significant decline in adaptive behavior and the temporal pattern of decline in specific functional skill domains were examined in 646 adults with mental retardation through 88 years of age. Cumulative incidence of significant decline for adults with Down syndrome increased from less than.04 at age 50 to.67 by age 72, whereas cumulative incidence of significant decline for adults with mental retardation without Down syndrome increased from less than.02 at age 50 to.52 at age 88. Among adults experiencing overall decline, four clusters of behaviors were identified based upon the sequence and magnitude of changes, suggesting a pattern of loss not unlike that noted in the population without mental retardation with dementia.

Elevated plasma amyloid beta-peptide 1-42 and onset of dementia in adults with Down syndrome

We compared levels of plasma amyloid beta-peptides Abeta1-42 and Abeta1-40 in 108 demented and nondemented adults with Down syndrome (DS) and 64 adults from the general population. Abeta1-42 and Abeta1-40 levels were significantly higher in adults with DS than in controls (P=0.0001). Compared to nondemented adults with DS, Abeta1-42 levels in demented adults with DS were selectively increased by 26% (28.2 pg/ml vs. 22.4 pg/ml, P=0.004). In addition, mean plasma levels of Abeta1-42 were 22% higher in DS cases with the apolipoprotein varepsilon4 allele than in DS subjects without an varepsilon4 allele (25.9 pg/ml vs. 21.2 pg/ml, P=0.01), while mean plasma levels of Abeta1-40 did not vary by APOE genotype. These results support the hypothesis that Abeta1-42 plays an important role in the pathogenesis of dementia associated with DS, as it does in Alzheimer's disease, and that variations in plasma levels may be related to disease progression.

Prevalence of chronic medical conditions in adults with mental retardation: comparison with the general population

We interviewed caregivers and reviewed medical records of 278 adults with mental retardation with and without Down syndrome, 45 to 74 years of age. Standardized morbidity ratios were used to compare frequency of medical disorders in these adults to frequency in the general population. In adults with mental retardation, the frequency of common age-related disorders was comparable to that in the general population, but there was an increased frequency of thyroid disorders, nonischemic heart disorders, and sensory impairment. Surveillance of health status and increased access to health care for screening and treatment of age-related disorders that are more frequent in adults with mental retardation would be important to prevent the development or delay the impact of these conditions and to promote healthy aging.