Low blood pressure in Down's syndrome, A link with Alzheimer's disease?

Insomnia Symptoms Are Associated with Measures of Functional Deterioration and Dementia Status in Adults with Down Syndrome at High Risk for Alzheimer's Disease

Background

While obstructive sleep apnea (OSA) and insomnia symptoms in neurotypical populations are associated with Alzheimer's disease (AD), their association with dementia in adults with Down syndrome (DS) remains less clear, even though these symptoms are prevalent and treatable in DS. Understanding their associations with AD-related dementia status, cognitive impairment, and functional deterioration may lead to interventions to slow decline or disease progression in adults with DS.

Objective

To characterize differences in OSA and insomnia symptom expression by dementia status, and to determine which sleep factors support dementia diagnosis.

Methods

Multimodal consensus conference was used to determine dementia status in 52 adults with DS (52.2 ± 6.4 years, 21 women). Cognitive impairment, adaptive behavior skills, and symptoms of OSA and insomnia were quantified using validated assessments for adults with DS and their primary informants.

Results

A sex by dementia status interaction demonstrated that older women with DS and dementia had more severe terminal insomnia but not OSA symptoms relative to older women with DS who were cognitively stable (CS). Greater insomnia symptom severity was associated with greater functional impairments in social and self-care domains adjusting for age, sex, premorbid intellectual impairment, and dementia status.

Conclusions

Insomnia symptoms are more severe in women with DS with dementia than in women with DS and no dementia, and regardless of dementia status or sex, more severe insomnia symptoms are associated with greater impairment in activities of daily living. These findings underscore the potential importance of early insomnia symptom evaluation and treatment in women with DS at risk of developing AD.

Cortical microinfarcts in adults with Down syndrome assessed with 3T-MRI

BACKGROUND

Cortical microinfarcts (CMI) were attributed to cerebrovascular disease and cerebral amyloid angiopathy (CAA). CAA is frequent in Down syndrome (DS) while hypertension is rare, yet no studies have assessed CMI in DS.

METHODS

We included 195 adults with DS, 63 with symptomatic sporadic Alzheimer's disease (AD), and 106 controls with 3T magnetic resonance imaging. We assessed CMI prevalence in each group and CMI association with age, AD clinical continuum, vascular risk factors, vascular neuroimaging findings, amyloid/tau/neurodegeneration biomarkers, and cognition in DS.

RESULTS

CMI prevalence was 11.8% in DS, 4.7% in controls, and 17.5% in sporadic AD. In DS, CMI increased in prevalence with age and the AD clinical continuum, was clustered in the parietal lobes, and was associated with lacunes and cortico-subcortical infarcts, but not hemorrhagic lesions.

DISCUSSION

In DS, CMI are posteriorly distributed and related to ischemic but not hemorrhagic findings suggesting they might be associated with a specific ischemic CAA phenotype.

HIGHLIGHTS

This is the first study to assess cortical microinfarcts (assessed with 3T magnetic resonance imaging) in adults with Down syndrome (DS). We studied the prevalence of cortical microinfarcts in DS and its relationship with age, the Alzheimer's disease (AD) clinical continuum, vascular risk factors, vascular neuroimaging findings, amyloid/tau/neurodegeneration biomarkers, and cognition. The prevalence of cortical microinfarcts was 11.8% in DS and increased with age and along the AD clinical continuum. Cortical microinfarcts were clustered in the parietal lobes, and were associated with lacunes and cortico-subcortical infarcts, but not hemorrhagic lesions. In DS, cortical microinfarcts are posteriorly distributed and related to ischemic but not hemorrhagic findings suggesting they might be associated with a specific ischemic phenotype of cerebral amyloid angiopathy.

A pathway linking pulse pressure to dementia in adults with Down syndrome

Adults with Down syndrome are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease and is linked to a diagnosis of dementia in adults with Down syndrome via structural imaging markers of cerebrovascular disease and atrophy. The study included participants with Down syndrome from the Alzheimer's Disease - Down Syndrome study (n = 195, age = 50.6 ± 7.2 years, 44% women, 18% diagnosed with dementia). Higher pulse pressure was associated with greater global, parietal and occipital white matter hyperintensity volume but not with enlarged perivascular spaces, microbleeds or infarcts. Using a structural equation model, we found that pulse pressure was associated with greater white matter hyperintensity volume, which in turn was related to increased neurodegeneration, and subsequent dementia diagnosis. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

Pathways linking pulse pressure to dementia in adults with Down syndrome

Individuals with Down syndrome (DS) are less likely to have hypertension than neurotypical adults. However, whether blood pressure measures are associated with brain health and clinical outcomes in this population has not been studied in detail. Here, we assessed whether pulse pressure is associated with markers of cerebrovascular disease, entorhinal cortical atrophy, and diagnosis of dementia in adults with DS. Participants with DS from the Biomarkers of Alzheimer's Disease in Adults with Down Syndrome study (ADDS; n=195, age=50.6±7.2 years, 44% women, 18% diagnosed with dementia) were included. Higher pulse pressure was associated with greater global, parietal, and occipital WMH volume. Pulse pressure was not related to enlarged PVS, microbleeds, infarcts, entorhinal cortical thickness, or dementia diagnosis. However, in a serial mediation model, we found that pulse pressure was indirectly related to dementia diagnosis through parieto-occipital WMH and, subsequently through entorhinal cortical thickness. Higher pulse pressure may be a risk factor for dementia in people with DS by promoting cerebrovascular disease, which in turn affects neurodegeneration. Pulse pressure is an important determinant of brain health and clinical outcomes in individuals with Down syndrome despite the low likelihood of frank hypertension.

Sex differences in cardiovascular disease and dysregulation in Down syndrome

This meta-analysis, which consisted of a scoping review and retrospective medical record review, is focused on potential sex differences in cardiovascular diseases in patients with Down syndrome. We limited our review to peer-reviewed, primary articles in the English language, in the PubMed and Web of Science databases from 1965 to 2021. Guidelines for scoping reviews were followed throughout the process. Four categorical domains were identified and searched using additional keywords: 1) congenital heart disease, 2) baseline physiology and risk factors, 3) heart disease and hypertension, and 4) stroke and cerebrovascular disease. Articles were included if they reported male and female distinct data, participants with Down syndrome, and one of our keywords. The retrospective medical record review was completed using 75 participating health care organizations to identify the incidence of congenital and cardiovascular diseases and to quantify cardiovascular risk factors in male and female patients. Female patients with Down syndrome are at higher risk of hypertension, ischemic heart disease, and cerebrovascular disease. The risk of congenital heart disease is higher in males with Down syndrome at all ages included in our analyses. Some of the male-to-female sex differences in cardiovascular disease risk in the general patient population are not present, or reversed in the Down syndrome population. This information should be considered for future investigations and ongoing patient care.NEW & NOTEWORTHY In patients with Down syndrome (DS), CHD is the leading cause of death <20 yr old and cardiovascular disease is a leading cause of death in individuals >20 yr old. Men with DS live longer than women. It is unknown if sex differences are present in cardiovascular disease and dysregulation in DS across the lifespan. We observed higher risk of hypertension, ischemic heart disease, and cerebrovascular disease in females and a higher risk of CHD in males with DS.

Cardiac Structure and Function in Adults with Down Syndrome

Various factors may alter the risk for cardiovascular disease in adults with Down syndrome (Ds), yet few studies have examined differences in cardiac physiology in this population. Previous research suggested lower systolic and diastolic function, but inconsistent methodologies and younger samples warrant research in adults with Ds. Our aim is to compare the cardiac structure and function of adults with Ds to age- and sex-matched adults without Ds. Echocardiography was used to assess systolic function, diastolic function, and cardiac structure in n = 19 adults (Ds n = 9, control n = 10). Regarding cardiac structure, adults with Ds had increased left ventricular posterior wall thickness at end-systole compared to adults without Ds (p = 0.007). Regarding systolic and diastolic function, adults with Ds were found to have lower septal peak systolic annular velocity (S') (p = 0.026), lower lateral and septal mitral annular early diastolic velocity (E') (p = 0.007 and p = 0.025, respectively), lower lateral peak mitral annular late diastolic velocity (A') (p = 0.027), and higher lateral and septal mitral annular early systolic velocity to diastolic velocity ratios (E/e') (p = 0.001 and p = 0.001, respectively). Differences in both cardiac structure and function were found when comparing adults with Ds to matched adults without Ds. Most of the differences were indicative of worse diastolic function.

Beyond amyloid: Immune, cerebrovascular, and metabolic contributions to Alzheimer disease in people with Down syndrome

People with Down syndrome (DS) have increased risk of Alzheimer disease (AD), presumably conferred through genetic predispositions arising from trisomy 21. These predispositions necessarily include triplication of the amyloid precursor protein (APP), but also other Ch21 genes that confer risk directly or through interactions with genes on other chromosomes. We discuss evidence that multiple genes on chromosome 21 are associated with metabolic dysfunction in DS. The resulting dysregulated pathways involve the immune system, leading to chronic inflammation; the cerebrovascular system, leading to disruption of the blood brain barrier (BBB); and cellular energy metabolism, promoting increased oxidative stress. In combination, these disruptions may produce a precarious biological milieu that, in the presence of accumulating amyloid, drives the pathophysiological cascade of AD in people with DS. Critically, mechanistic drivers of this dysfunction may be targetable in future clinical trials of pharmaceutical and/or lifestyle interventions.

Redox Switches Controlling Nitric Oxide Signaling in the Resistance Vasculature and Implications for Blood Pressure Regulation: Mid-Career Award for Research Excellence 2020

The arterial resistance vasculature modulates blood pressure and flow to match oxygen delivery to tissue metabolic demand. As such, resistance arteries and arterioles have evolved a series of highly orchestrated cell-cell communication mechanisms between endothelial cells and vascular smooth muscle cells to regulate vascular tone. In response to neurohormonal agonists, release of several intracellular molecules, including nitric oxide, evokes changes in vascular tone. We and others have uncovered novel redox switches in the walls of resistance arteries that govern nitric oxide compartmentalization and diffusion. In this review, we discuss our current understanding of redox switches controlling nitric oxide signaling in endothelial and vascular smooth muscle cells, focusing on new mechanistic insights, physiological and pathophysiological implications, and advances in therapeutic strategies for hypertension and other diseases.

Impact of acute kidney injury in patients prescribed angiotensin-converting enzyme inhibitors over the first two years of life

BACKGROUND

The association of long-term acute kidney injury (AKI) risk with angiotensin-converting enzyme (ACE) inhibitor use in neonates/infants is poorly understood. We examined this association to identify potential AKI risk factors.

METHODS

We retrospectively evaluated 119 children aged < 2 years (72 boys; median age, 5.0 months) who received ACE inhibitors for congenital heart disease for ≥ 6 months between January 2009 and June 2019. We monitored the occurrence of AKI, defined according to the Kidney Disease Improving Global Outcomes guidelines. Demographic and clinical data were extracted from medical records. Risk factors associated with AKI onset were identified by a Cox proportional hazards regression analysis of variables previously identified as risk factors of AKI and those significant in a univariate analysis.

RESULTS

Thirty-three of 119 patients (28%) developed AKI at a median follow-up of 1.3 years (interquartile range, 0.8-3.2 years). AKI incidence was 1257 events per 10,000 patient-years. Concomitant tolvaptan use (hazard ratio [HR], 3.81; 95% confidence interval [CI], 1.82-7.97; P < 0.01) and Down syndrome (HR, 3.22; 95% CI, 1.43-7.29; P < 0.01) were identified as independent risk factors of AKI onset.

CONCLUSIONS

AKI was strongly associated with concomitant tolvaptan use and Down syndrome in our study population. Physicians should consider these factors when prescribing ACE inhibitors for neonates/infants. Low-dose ACE inhibitors slow CKD progression because of their antifibrotic properties. ACE inhibitors may be beneficial for patients with Down syndrome who have underlying CKD in a non-acute setting. Therefore, they should be administered to such patients with caution.

Increased choroidal thickness in adults with Down syndrome

INTRODUCTION

People with Down syndrome (DS) are particularly susceptible to Alzheimer's disease (AD) due to the triplication of the amyloid precursor protein (APP) gene. In this cross-sectional study, we hypothesized that choroidal thinning reported in sporadic AD (sAD) is mirrored in adults with DS.

METHODS

The posterior pole of the eye for 24 adults with DS and 16 age-matched controls (Ctrl) were imaged with optical coherence tomography. Choroidal thickness (ChT) was measured and analyzed in relation to cognitive status and cerebral amyloid beta (Aβ) load.

RESULTS

ChT was increased in people with DS (pwDS) compared to Ctrl. This increase was associated with gender differences and positively correlated with cerebral Aβ load in a small subset. There was no significant correlation detected between ChT and age or cognitive status.

DISCUSSION

In contrast to sAD this study found a significantly thicker choroid in pwDS. Whether these changes are related to Aβ pathology in DS needs further investigation.

Quantitative Analysis of Retinal Structure and Function in Two Chromosomally Altered Mouse Models of Down Syndrome

Purpose

Ophthalmic disorders are among the most prevalent Down syndrome (DS) comorbidities. Therefore, when studying mouse models of DS, ignoring how vision is affected can lead to misinterpretation of results from assessments dependent on the integrity of the visual system. Here, we used imaging and electroretinography (ERG) to study eye structure and function in two important mouse models of DS: Ts65Dn and Dp(16)1Yey/+.

Methods

Cornea and anterior segment were examined with a slit-lamp. Thickness of retinal layers was quantified by optical coherence tomography (OCT). Eye and lens dimensions were measured by magnetic resonance imaging (MRI). Retinal vasculature parameters were assessed by bright field and fluorescent imaging, and by retinal flat-mount preparations. Ganzfeld ERG responses to flash stimuli were used to assess retinal function in adult mice.

Results

Total retinal thickness is significantly increased in Ts65Dn and Dp(16)1Yey/+ compared with control mice, because of increased thickness of inner retinal layers, including the inner nuclear layer (INL). Increased retinal vessel caliber was found in both chromosomally altered mice when compared with controls. ERG responses in Ts65Dn and Dp(16)1Yey/+ mice showed subtle alterations compared with controls. These, however, seemed to be unrelated to the thickness of the INL, but instead dependent on the anesthetic agent used (ketamine, tribromoethanol, or urethane).

Conclusions

We provide evidence of retinal alterations in Ts65Dn and Dp(16)1Yey/+ mice that are similar to those reported in persons with DS. Our ERG results are also a reminder that consideration should be given to the choice of anesthetic agents in such experiments.

Hypertension in Adults With Intellectual Disability: Prevalence and Risk Factors

INTRODUCTION

Individuals with intellectual disability have a high prevalence of obesity and low physical activity levels, which are risk factors for hypertension. This study estimated the prevalence of hypertension in a global data set of adults with intellectual disability participating in Special Olympics and investigated the role of physical activity and obesity in hypertension risk.

METHODS

A total of 33,122 individuals aged ≥18 years with intellectual disability who participated in Special Olympic events from 2014 to 2018 had their brachial blood pressure, BMI, and self-reported physical activity assessed. Hypertension was classified using 2017 American College of Cardiology/American Heart Association guidelines (systolic blood pressure≥130 mmHg and diastolic blood pressure≥80 mmHg). Data were analyzed in 2019.

RESULTS

Participants were aged 31 (SD=11) years, 64% male, and had a resting blood pressure of 121 (SD=16)/76 (SD=12) mmHg. The population was 48% (95% CI=47.5%, 48.6%) hypertensive. Male participants had a higher prevalence of hypertension (50.7%, 95% CI=50.1%, 51.4%) than female participants (43.1%, 95% CI=42.2%, 44.0%), with prevalence increasing with age. Odds of hypertension increased when performing no or insufficient physical activity and with increasing obesity (p<0.01), tripling (OR=3.06, 3.66) for all individuals who performed no physical activity except for those of normal weight (OR=1.72), and doubling (OR=2.13-3.87) for individuals who were obese or morbidly obese across all physical activity levels.

CONCLUSIONS

This study is the first to determine population-based prevalence rates of hypertension in individuals with intellectual disability. It highlights the similarity in prevalence to the general population. The results emphasize the importance of population-wide screening, increasing physical activity, and reducing obesity in decreasing cardiovascular risk in this population.

The re-emerging pathophysiological role of the cystathionine-β-synthase - hydrogen sulfide system in Down syndrome

Down syndrome (DS) is associated with significant perturbances in many morphological and biochemical features. Cystathionine-β-synthase (CBS) is one of the key mammalian enzymes that is responsible for the biological production of the gaseous transmitter hydrogen sulfide (H₂ S). When H₂ S is overproduced, it can exert detrimental cellular effects, in part due to inhibition of mitochondrial Complex IV activity. An increased expression of CBS and the consequent overproduction of H₂ S are well documented in individuals with DS. Two decades ago, it has been proposed that a toxic overproduction of H₂ S importantly contributes to the metabolic and neurological deficits associated with DS. However, until recently, this hypothesis has not yet been tested experimentally. Recent data generated in human dermal fibroblasts show that DS cells overproduce H₂ S, which, in turn, suppresses mitochondrial Complex IV activity and impairs mitochondrial oxygen consumption and ATP generation. Therapeutic CBS inhibition lifts the tonic (and reversible) suppression of Complex IV: This results in the normalization of mitochondrial function in DS cells. H₂ S may also contribute to the cellular dysfunction via several other molecular mechanisms through interactions with various mitochondrial and extramitochondrial molecular targets. The current article provides a historical background of the field, summarizes the recently published data and their potential implications, and outlines potential translational approaches (such as CBS inhibition and H₂ S neutralization) and future experimental studies in this re-emerging field of pathobiochemistry.

Diminished Blood Pressure Profiles in Children With Down Syndrome

This study sought to analyze blood pressure trends in children with Down syndrome at multiple centers. A multicenter, retrospective, cross-sectional study was performed. All patients were <18 years and had a diagnosis of Down syndrome. Existing comorbidities were nonexclusionary. For each patient, 3 blood pressure recordings were obtained from routine clinic visits. In total, 887 patients with 2661 total blood pressure recordings were included in this study. The average blood pressure percentile for patients was 38.87 with a median percentile of 31.5. Age, sex, and race were not predictive of blood pressure percentile. Compared with established data from the National Heart Lung and Blood Institute and National Health and Nutrition Examination Survey cohort (ages 8-18 years), blood pressure in our Down syndrome population was statistically lower by 6.1 percentile points (P<0.001), with the greatest difference at higher blood pressure percentiles (P<0.001). Only 10% of all Down syndrome cohort blood pressure recordings were greater than the National Heart Lung and Blood Institute/National Health and Nutrition Examination Survey 70th percentile, with no patients meeting criteria for prehypertension or hypertension. Additional comparisons against American Academy of Pediatrics data were similar and statistically significant. In children with Down syndrome, there is a 12 percentile point reduction in baseline blood pressure compared with age- and height-matched controls reported in the National Heart Lung and Blood Institute/National Health and Nutrition Examination Survey and American Academy of Pediatrics cohorts. This data can potentially be utilized in the evaluation and care of persons with Down syndrome in their pediatric medical homes.

Cross-Sectional Study of Arterial Stiffness in Adolescents with Down Syndrome

OBJECTIVES

To test whether youth with Down syndrome have aortic stiffness indices, as measured by pulse wave velocity (PWV), that differ from youth without Down syndrome and to compare reference-based age-adjusted (age-PWV-Z) and height-adjusted (Ht-PWV-Z) in youth with and without Down syndrome.

STUDY DESIGN

Cross-sectional study of PWV in 129 adolescents with Down syndrome and 97 youth of comparable age, sex, race/ethnicity, and body mass index (BMI). PWV, age-PWV-Z, and Ht-PWV-Z were compared. Regression models were developed to test for associations with PWV.

RESULTS

Youth with Down syndrome and controls were comparable in BMI-Z (1.4 [-1.5 to 2.8] vs 1.2 [-2.0 to 2.8], P = .57) but not Ht-Z (-2.3 [-4.7 to 0.8] vs 0.4 [-2.0 to 2.6], P < .0001). PWV (m/s, 5.0 [3.1-7.9] vs 5.0 [3.6-8.0], P = .5) and mean arterial pressure (MAP, mm Hg) (78 [61-102] vs 74 [64-97], P = .09) were not different between groups. In adjusted analyses confined to Down syndrome, PWV was associated only with BMI, but not age, black race, or MAP (R2 = 0.11). In contrast, BMI, age, black race, and MAP were all positively associated with and better explained PWV in controls (R2 = 0.50). PWV was not associated with height in youth with or without Down syndrome. Although age-PWV-Z was not different in Down syndrome (-0.36 [-2.93 to 3.49]) vs -0.15 [-2.32 to 3.22]), Ht-PWV-Z was greater in Down syndrome (0.32 [-2.28 to 4.07] vs -0.08 [-2.64 to 2.64], P = .002), and Ht-PWV-Z was greater than age-PWV-Z in Down syndrome (P < .0001).

CONCLUSIONS

The lack of relationship of PWV, an independent predictor of adult cardiovascular events, with its traditional determinants including MAP suggests Down syndrome-specific phenomena may alter such relationships in this population. In youth with Down syndrome, Ht-adjusted PWV may overestimate aortic stiffness.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT01821300.

Blood Pressure Elevation and Risk of Moyamoya Syndrome in Patients With Trisomy 21

OBJECTIVES

Individuals with Down syndrome (DS) are at risk for the development of moyamoya syndrome (MMS); MMS is often recognized only after a resulting stroke has occurred. Our goal with this study was to determine if elevations in blood pressure (BP) precede acute presentation of MMS in individuals with DS.

METHODS

A single-center, retrospective case-control study was performed. Thirty patients with MMS and DS and 116 patients with DS only were identified retrospectively. Three BP recordings were evaluated at set intervals (18-24 months, 12-18 months, and 6-12 months before diagnosis of MMS). These were then compared against control averages from patients with DS only. To assess changes over the time, we used general linear model repeated measures analysis of variance. To identify independent predictors of MMS and DS, we used a multivariable analysis using generalized estimating equations accounting for repeated measures of BP.

RESULTS

BP in patients with MMS and DS rose significantly over the 24-month period preceding presentation (34th, 42nd, and 70th percentiles at the 18-24-month, 12-18-month, and 6-12-month periods, respectively). BPs in the patients with both MMS and DS were significantly higher than in the DS-only controls in the 6 to 12 (P < .001) and 12 to 18 months before presentation (P = .016). Higher Suzuki scores, bilateral disease, and posterior circulation involvement were also predictive of BP elevation before presentation.

CONCLUSIONS

Elevations in BP may foreshadow presentation of MMS in individuals with DS. This simple, low-cost screening measure may lead to early identification of at-risk patients in the medical home and prevent irreversible neurologic injury.

Acute effects of cycling exercise on post-exercise blood pressure in individuals with down syndrome

Purpose. Studies have shown that even a single session of physical exercise lowers blood pressure after its completion. This phenomenon is called post-exercise hypotension (PEH) and has been considered as a non-pharmacological treatment to control blood pressure. However, there are no studies regarding the occurrence of PEH after acute exercise in individuals with Down syndrome (DS). This study aimed to analyse the occurrence of PEH in these subjects and the possible role of exercise intensity. Methods. Ten individuals with DS, of both genders, participated in the study (age, 29 ± 7 years; body mass, 60.7 ± 9 kg; height, 1.48 ± 0.11 m; BMI, 27.6 ± 2.4 kg/m2). The volunteers randomly underwent 2 sessions of exercise on a stationary bike for 20 minutes and 1 control session. Heart rate, systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured after 15 minutes of resting, in the 20

Cerebrovascular pathology in Down syndrome and Alzheimer disease

People with Down syndrome (DS) are at high risk for developing Alzheimer disease (AD) with age. Typically, by age 40 years, most people with DS have sufficient neuropathology for an AD diagnosis. Interestingly, atherosclerosis and hypertension are atypical in DS with age, suggesting the lack of these vascular risk factors may be associated with reduced cerebrovascular pathology. However, because the extra copy of APP leads to increased beta-amyloid peptide (Aβ) accumulation in DS, we hypothesized that there would be more extensive and widespread cerebral amyloid angiopathy (CAA) with age in DS relative to sporadic AD. To test this hypothesis CAA, atherosclerosis and arteriolosclerosis were used as measures of cerebrovascular pathology and compared in post mortem tissue from individuals with DS (n = 32), sporadic AD (n = 80) and controls (n = 37). CAA was observed with significantly higher frequencies in brains of individuals with DS compared to sporadic AD and controls. Atherosclerosis and arteriolosclerosis were rare in the cases with DS. CAA in DS may be a target for future interventional clinical trials.

Management and prevalence of long-term conditions in primary health care for adults with intellectual disabilities compared with the general population: A population-based cohort study

BACKGROUND

In the UK, general practitioners/family physicians receive pay for performance on management of long-term conditions, according to best-practice indicators.

METHOD

Management of long-term conditions was compared between 721 adults with intellectual disabilities and the general population (n = 764,672). Prevalence of long-term conditions was determined, and associated factors were investigated via logistic regression analyses.

RESULTS

Adults with intellectual disabilities received significantly poorer management of all long-term conditions on 38/57 (66.7%) indicators. Achievement was high (75.1%-100%) for only 19.6% of adults with intellectual disabilities, compared with 76.8% of the general population. Adults with intellectual disabilities had higher rates of epilepsy, psychosis, hypothyroidism, asthma, diabetes and heart failure. There were no clear associations with neighbourhood deprivation.

CONCLUSIONS

Adults with intellectual disabilities receive poorer care, despite conditions being more prevalent. The imperative now is to find practical, implementable means of supporting the challenges that general practices face in delivering equitable care.

Blood pressure levels and body mass index in Brazilian adults with Down syndrome

CONTEXT AND OBJECTIVE

Increased life expectancy among people with Down syndrome (DS) has introduced new environmental factors that may affect blood pressure (BP) and/or lead to obesity in this population. The aim here was to investigate BP levels and body mass index (BMI) in adults with DS, correlating these data with the patients' sex and age.

DESIGN AND SETTING

Analytical cross-sectional observational study conducted in special schools in Curitiba (PR), Brazil.

METHODS

97 adult patients were included. BP was measured in accordance with the established guidelines. BMI was calculated by dividing the weight by the height squared (kg/m2).

RESULTS

Sex had no influence on BMI; nor did systolic BP (SBP) or diastolic BP (DBP). The age range was from 18 to 56 years. No correlation was observed between increasing age and greater BMI or BP. Eighty-six individuals (88.7%) presented normal BP, eleven (11.3%) prehypertension and none hypertension. Twenty patients (20.4%) presented BP lower than 90 × 60 mmHg. BMI ranged from 18 to 48 kg/m2 (mean of 28.8 ± 3.92 kg/m2): 21.9% had normal weight; 40.7% were overweight; and 25.3% had obesity class I, 9.9% class II and 2.2% class III. Higher BMI was associated with significantly greater SBP and DBP (P = 0.0175 and P = 0.0015).

CONCLUSION

Sex and age did not influence SBP, DBP or BMI in Brazilian adults with DS. Higher BMI was associated with greater BP (both systolic and diastolic).

(1)H-MRS metabolites in adults with Down syndrome: Effects of dementia

To determine if proton magnetic resonance spectroscopy (¹H-MRS) detect differences in dementia status in adults with Down syndrome (DS), we used ¹H-MRS to measure neuronal and glial metabolites in the posterior cingulate cortex in 22 adults with DS and in 15 age- and gender-matched healthy controls. We evaluated associations between ¹H-MRS results and cognition among DS participants. Neuronal biomarkers, including N-acetylaspartate (NAA) and glutamate-glutamine complex (Glx), were significantly lower in DS patients with Alzheimer's should probably be changed to Alzheimer (without ' or s) through ms as per the new naming standard disease (DSAD) when compared to non-demented DS (DS) and healthy controls (CTL). Neuronal biomarkers therefore appear to reflect dementia status in DS. In contrast, all DS participants had significantly higher myo-inositol (MI), a putative glial biomarker, compared to CTL. Our data indicate that there may be an overall higher glial inflammatory component in DS compared to CTL prior to and possibly independent of developing dementia. When computing the NAA to MI ratio, we found that presence or absence of dementia could be distinguished in DS. NAA, Glx, and NAA/MI in all DS participants were correlated with scores from the Brief Praxis Test and the Severe Impairment Battery. ¹H-MRS may be a useful diagnostic tool in future longitudinal studies to measure AD progression in persons with DS. In particular, NAA and the NAA/MI ratio is sensitive to the functional status of adults with DS, including prior to dementia.

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¹H-MRS was used to compare demented and nondemented adults with Down syndrome.

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Neuronal biomarkers were lowest in demented adults with Down syndrome.

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Glial biomarkers including myoinositol were higher in demented adults with DS.

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Neuronal and glial biomarkers were correlated with cognition in Down syndrome.

Morbidity and medication in a large population of individuals with Down syndrome compared to the general population

AIM

The aim of this study was to describe the incidence of morbidities and the prevalence of medical prescriptions in a large Down syndrome population.

METHOD

A retrospective cohort study was carried out using the UK Clinical Practice Research Datalink from 1 January 2004 to 31 December 2013. We matched individuals with Down syndrome to randomly selected control participants by practice site, sex, birth year, and recording period.

RESULTS

A total of 6430 individuals with Down syndrome (3009 females, 3421 males) and 19 176 controls (8966 females, 10,210 males) were included in the study. The incidence of cardiovascular disorders, gastrointestinal diseases (incidence rate ratio [IRR] 7.9 at 3 to <6y: yearly prevalence ratio [YPR] for laxatives 4.7), and sleeping disorders (IRR 4.8 in 3 to <6y) was increased in children with Down syndrome versus control participants. New onset of congenital heart malformation, ear diseases, eye disorders, autism, hypothyroidism, diabetes, and obesity were more frequent in childhood and remained elevated in adulthood (overall IRR 35.5, 1.7, 3.1, 4.4, 13.1, 1.3, and 2.6 respectively), whereas the gap widened in adulthood for epilepsy and intellectual disability (IRR 15.2 and 158 respectively, in participants older than 30y). At ≥ 30 years, the incidence of hypotension and dementia was raised (IRR 3.0 and 92.1 respectively; YPR for dementia drugs: 76.3); and that of hypertension, depression and anxiety was lowered (IRR 0.2, 0.5, and 0.4 respectively).

INTERPRETATION

The profile of newly occurring morbidities in Down syndrome varies across the developmental lifespan.

Aging in Down Syndrome and the Development of Alzheimer's Disease Neuropathology

Chromosome 21, triplicated in Down Syndrome, contains several genes that are thought to play a critical role in the development of AD neuropathology. The overexpression of the gene for the amyloid precursor protein (APP), on chromosome 21, leads to early onset beta-amyloid (Aβ) plaques in DS. In addition to Aβ accumulation, middle-aged people with DS develop neurofibrillary tangles, cerebrovascular pathology, white matter pathology, oxidative damage, neuroinflammation and neuron loss. There is also evidence of potential compensatory responses in DS that benefit the brain and delay the onset of dementia after there is sufficient neuropathology for a diagnosis of AD. This review describes some of the existing literature and also highlights gaps in our knowledge regarding AD neuropathology in DS. It will be critical in the future to develop networked brain banks with standardized collection procedures to fully characterize the regional and temporal pathological events associated with aging in DS. As more information is acquired regarding AD evolution in DS, there will be opportunities to develop interventions that are age-appropriate to delay AD in DS.

Cerebrovascular contributions to aging and Alzheimer's disease in Down syndrome

Down syndrome (DS) is a common cause of intellectual disability and is also associated with early age of onset of Alzheimer's disease (AD). Due to an extra copy of chromosome 21, most adults over 40years old with DS have beta-amyloid plaques as a result of overexpression of the amyloid precursor protein. Cerebrovascular pathology may also be a significant contributor to neuropathology observed in the brains of adults with DS. This review describes the features of cardiovascular dysfunction and cerebrovascular pathology in DS that may be modifiable risk factors and thus targets for interventions. We will describe cerebrovascular pathology, the role of co-morbidities, imaging studies indicating vascular pathology and the possible consequences. It is clear that our understanding of aging and AD in people with DS will benefit from further studies to determine the role that cerebrovascular dysfunction contributes to cognitive health. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Long-segment thoracoabdominal aortic coarctation in a child with Down syndrome

Midaortic syndrome is a rare vascular anomaly characterized by coarctation of the descending thoracic and abdominal aorta. Down syndrome is associated with multiple congenital cardiac malformations but is rarely associated with developmental vascular anomalies. Midaortic syndrome may result in severe renovascular hypertension that requires early intervention to prevent life-threatening complications. We report a child with Down syndrome who presented with occlusion of the aorta and was treated with aortic bypass. More than 4 years after the procedure, the patient's renal function remains normal, and there is no evidence of recurrent hypertension. Long-term follow-up is important to assess the benefits of surgical repair.

"Down syndrome: an insight of the disease"

Down syndrome (DS) is one of the commonest disorders with huge medical and social cost. DS is associated with number of phenotypes including congenital heart defects, leukemia, Alzeihmer's disease, Hirschsprung disease etc. DS individuals are affected by these phenotypes to a variable extent thus understanding the cause of this variation is a key challenge. In the present review article, we emphasize an overview of DS, DS-associated phenotypes diagnosis and management of the disease. The genes or miRNA involved in Down syndrome associated Alzheimer's disease, congenital heart defects (AVSD), leukemia including AMKL and ALL, hypertension and Hirschprung disease are discussed in this article. Moreover, we have also reviewed various prenatal diagnostic method from karyotyping to rapid molecular methods -  MLPA, FISH, QF-PCR, PSQ, NGS and noninvasive prenatal diagnosis in detail.

Blood Pressure and Hemodynamic Adaptations after a Training Program in Young Individuals with Down Syndrome

BACKGROUND

Cardiovascular diseases affect people worldwide. Individuals with Down Syndrome (DS) have an up to sixteen-time greater risk of mortality from cardiovascular diseases.

OBJECTIVE

To evaluate the effects of aerobic and resistance exercises on blood pressure and hemodynamic variables of young individuals with DS.

METHODS

A total of 29 young individuals with DS participated in the study. They were divided into two groups: aerobic training (AT) (n = 14), and resistance training (TR) (n = 15). Their mean age was 15.7 ± 2.82 years. The training program lasted 12 weeks, and had a frequency of three times a week for AT and twice a week for RT. AT was performed in treadmill/ bicycle ergometer, at an intensity between 50%-70% of the HR reserve. RT comprised nine exercises with three sets of 12 repetition-maximum. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP) and hemodynamic variables were assessed beat-to-beat using the Finometer device before/after the training program. Descriptive analysis, the Shapiro-Wilk test to check the normality of data, and the two-way ANOVA for repeated measures were used to compare pre- and post-training variables. The Pearson's correlation coefficient was calculated to correlate hemodynamic variables. The SPSS version 18.0 was used with the significance level set at p < 0.05.

RESULTS

After twelve weeks of aerobic and/or resistance training, significant reductions in variables SBP, DBP and MBP were observed.

CONCLUSION

This study suggests a chronic hypotensive effect of moderate aerobic and resistance exercises on young individuals with DS.

Evaluation of cardiac functions with Doppler echocardiography in children with Down syndrome and anatomically normal heart

OBJECTIVE

To study the cardiac functions in Down syndrome children who did not have structural cardiac lesion by conventional and tissue Doppler echocardiography.

MATERIALS AND METHODS

A total of 85 children with Down syndrome without anatomic heart disease and 50 normal control children were subjected to the assessment of right and left ventricular functions by both two-dimensional and tissue Doppler echocardiography.

RESULTS

Children with Down syndrome had significantly higher left ventricular ejection fraction detected by two-dimensional echocardiography and left ventricular diastolic dysfunction detected by tissue Doppler than observed in the controls. In addition, children with Down syndrome also had right ventricular systolic and diastolic dysfunctions. Children with Down syndrome had significantly higher pulmonary artery systolic pressure than the control children. There was no significant difference in the cardiac functions between children with non-disjunction Down syndrome and those with the translocation type.

CONCLUSION

Despite an apparently normal heart, children with Down syndrome may have silent disturbed cardiac functions, which may be detected by two-dimensional or tissue Doppler echocardiography. This may have an important clinical implication, especially before involving Down syndrome children in surgery or strenuous exercise.

Regulation of the MIR155 host gene in physiological and pathological processes

MicroRNAs (miRNAs), a family of small nonprotein-coding RNAs, play a critical role in posttranscriptional gene regulation by acting as adaptors for the miRNA-induced silencing complex to inhibit gene expression by targeting mRNAs for translational repression and/or cleavage. miR-155-5p and miR-155-3p are processed from the B-cell Integration Cluster (BIC) gene (now designated, MIR155 host gene or MIR155HG). MiR-155-5p is highly expressed in both activated B- and T-cells and in monocytes/macrophages. MiR-155-5p is one of the best characterized miRNAs and recent data indicate that miR-155-5p plays a critical role in various physiological and pathological processes such as hematopoietic lineage differentiation, immunity, inflammation, viral infections, cancer, cardiovascular disease, and Down syndrome. In this review we summarize the mechanisms by which MIR155HG expression can be regulated. Given that the pathologies mediated by miR-155-5p result from the over-expression of this miRNA it may be possible to therapeutically attenuate miR-155-5p levels in the treatment of several pathological processes.

Neurobiological elements of cognitive dysfunction in down syndrome: exploring the role of APP

Down syndrome (DS) is the most common cause of cognitive dysfunction in children. Additionally, most adults with DS will eventually show both clinical and neuropathologic hallmarks of Alzheimer's disease (AD). The hippocampal formation constitutes the primary target for degeneration in both AD and DS. Over the past few years, we have studied the molecular mechanisms behind degeneration of this region and its major inputs in mouse models of DS. Our investigation has suggested that the loss of hippocampal inputs, particularly cholinergic and noradrenergic terminals, leads to de-afferentation of this region in the Ts65Dn mouse model of DS. Interestingly, we were able to link the overexpression of amyloid precursor protein (App) gene to degeneration of cholinergic and noradrenergic neurons in DS mouse models. We examined the underlying mechanisms of degeneration of multiple systems with extensive projections to the hippocampus in DS and its mouse models and the role of App overexpression in neurodegeneration. Understanding mechanisms behind hippocampal dysfunction has helped us to test several therapeutic strategies successfully in mouse models of DS. Here we review these strategies and mechanisms and discuss ways to translate our findings into possible interventions in humans.

Genomic determinants in the phenotypic variability of Down syndrome

Down syndrome caused by trisomy 21 is a collection of phenotypes with variable expressivity and penetrance. The significant advances in exploring the human genome now provide the tools to better understand the contribution of trisomy 21 in the different manifestations of Down syndrome, and the functional links between the genome variability and the phenotypic variability.

Stiffness of the large arteries in individuals with and without Down syndrome

BACKGROUND

Down syndrome is known to cause premature aging in several organ systems. However, it remains unclear whether this aging effect also affects the structure and function of the large arterial trunks. In this controlled study, the possibility of changes in the large arteries due to aging was evaluated in patients with Down syndrome.

METHODS

Eighty-two subjects of both genders were selected. The Down syndrome group had 41 active subjects consisting of 19 males and 22 females (mean age 21 ± 1, range 13-42 years) without cardiovascular complications and who did not use vasoactive drugs. The control group consisted of 41 healthy individuals without trisomy 21 of the same gender and age as the Down syndrome group and who did not use vasoactive medication. Carotid-femoral pulse wave velocity was obtained as an index of aortic stiffness using an automatic noninvasive method.

RESULTS

Individuals with Down syndrome had significantly lower blood pressure than those in the control group. Systolic blood pressure for the Down syndrome group and control group was 106 ± 2 mmHg vs 117 ± 2 mmHg (P < 0.001), respectively; diastolic blood pressure was 66 ± 2 mmHg vs 77 ± 2 mmHg (P < 0.001); and mean arterial pressure was 80 ± 1 mmHg vs 90 ± 1 mmHg (P < 0.001). Only age and systolic blood pressure were shown to correlate significantly with pulse wave velocity, but the slopes of the linear regression curves of these two variables showed no significant difference between the two study groups. Pulse wave velocity, which was initially significantly lower in the Down syndrome group (7.51 ± 0.14 m/s vs 7.84 ± 0.12 m/s; P <0.05), was similar between the groups after systolic blood pressure adjustment (7.62 ± 0.13 m/s vs 7.73 ± 0.13 m/s).

CONCLUSION

Despite evidence in the literature that patients with Down syndrome undergo early aging, this process does not seem to affect the large arterial trunks, given that values of carotid-femoral pulse wave velocity were similar in individuals with or without trisomy 21. Considering that Down syndrome presents with chronic hypotension, it is reasonable to propose that the prolonged reduction of arterial distending pressure may contribute to functional preservation of the arteries in patients with Down syndrome.

Trisomy-21 gene dosage over-expression of miRNAs results in the haploinsufficiency of specific target proteins

Down syndrome (DS) or Trisomy 21 (Ts21) is caused by the presence of an extra copy of all or part of human chromosome 21 (Hsa21) and is the most frequent survivable congenital chromosomal abnormality. Bioinformatic annotation has established that Hsa21 harbors more than 400 genes, including five microRNA (miRNA) genes (miR-99a, let-7c, miR-125b-2, miR-155, and miR-802). MiRNAs are endogenous, single-stranded, small non-coding RNA molecules that regulate gene expression by interacting with specific recognition elements harbored within the 3'-untranslated region (3'-UTR) of mRNAs and subsequently target these mRNAs for translational repression or destabilization. MiRNA expression profiling, miRNA RT-PCR, and miRNA in situ hybridization experiments have demonstrated that Hsa21-derived miRNAs were over-expressed in fetal brain and heart specimens isolated from individuals with DS. We now propose that Ts21 gene dosage over-expression of Hsa21-derived miRNAs in DS individuals result in the decreased expression of specific target proteins (i.e. haploinsufficiency) that contribute, in part, to the DS phenotype.

Down syndrome--recent progress and future prospects

Down syndrome (DS) is caused by trisomy of chromosome 21 (Hsa21) and is associated with a number of deleterious phenotypes, including learning disability, heart defects, early-onset Alzheimer's disease and childhood leukaemia. Individuals with DS are affected by these phenotypes to a variable extent; understanding the cause of this variation is a key challenge. Here, we review recent research progress in DS, both in patients and relevant animal models. In particular, we highlight exciting advances in therapy to improve cognitive function in people with DS and the significant developments in understanding the gene content of Hsa21. Moreover, we discuss future research directions in light of new technologies. In particular, the use of chromosome engineering to generate new trisomic mouse models and large-scale studies of genotype–phenotype relationships in patients are likely to significantly contribute to the future understanding of DS.

Prevalence of hypertension in adults with intellectual disability in the Netherlands

BACKGROUND

Literature on the prevalence of hypertension in people with intellectual disability (ID) is mostly based on file studies or on measurements limited to the age group below 50 years. We measured and calculated the prevalence of hypertension in adults with ID and studied the distribution of hypertension in relation to age, gender, diagnosis of Down's syndrome and level of ID.

METHODS

In an observational cross-sectional study, standardized blood pressure measurements were obtained from 258 randomly selected adult clients of three Dutch care providers for people with ID. Hypertension was defined as a mean systolic blood pressure above 140 mm Hg on repeated measurements.

RESULTS

The overall prevalence rate of hypertension was 17.4% (95% CI 12.28-22.46). This was comparable to the prevalence in the general Dutch population. No accurate blood pressure measurement could be performed in 28.4% of people with severe and profound ID owing to repetitive physical activity or resistance. Hypertension was significantly related to older age and absence of Down's syndrome; no correlation with gender or level of ID could be shown.

RECOMMENDATION

The risk factor hypertension should be detected and treated in the same manner as in the general population following national guidelines.

Functional genetic variation of human miRNAs and phenotypic consequences

A large number of human protein-coding genes are finely regulated by one or more microRNAs. Members of this small noncoding RNA family have emerged as important post-transcriptional regulators of gene expression and are involved in a number of disease phenotypes. Variability in the human genome is extensive and includes the common and rare single nucleotide polymorphisms (SNPs) and copy number variations (CNVs). The functional significance of the genome's variability is under intense investigation. In this article we review the emerging literature on how human genomic variation influences the outcome of microRNA targeting and the associated phenotypic effects. Illustrative examples are discussed that demonstrate the biological importance of functional polymorphisms affecting miRNA-mediated gene regulation.

Human microRNA-155 on chromosome 21 differentially interacts with its polymorphic target in the AGTR1 3' untranslated region: a mechanism for functional single-nucleotide polymorphisms related to phenotypes

Animal microRNAs (miRNAs) regulate gene expression through base pairing to their targets within the 3' untranslated region (UTR) of protein-coding genes. Single-nucleotide polymorphisms (SNPs) located within such target sites can affect miRNA regulation. We mapped annotated SNPs onto a collection of experimentally supported human miRNA targets. Of the 143 experimentally supported human target sites, 9 contain 12 SNPs. We further experimentally investigated one of these target sites for hsa-miR-155, within the 3' UTR of the human AGTR1 gene that contains SNP rs5186. Using reporter silencing assays, we show that hsa-miR-155 down-regulates the expression of only the 1166A, and not the 1166C, allele of rs5186. Remarkably, the 1166C allele has been associated with hypertension in many studies. Thus, the 1166C allele may be functionally associated with hypertension by abrogating regulation by hsa-miR-155, thereby elevating AGTR1 levels. Since hsa-miR-155 is on chromosome 21, we hypothesize that the observed lower blood pressure in trisomy 21 is partially caused by the overexpression of hsa-miR-155 leading to allele-specific underexpression of AGTR1. Indeed, we have shown in fibroblasts from monozygotic twins discordant for trisomy 21 that levels of AGTR1 protein are lower in trisomy 21.

The vascular endothelium in hypertension

The vascular endothelium plays a fundamental role in the basal and dynamic regulation of the circulation. Thus, it has a crucial role in the pathogenesis of hypertension. A spectrum of vasoactive substances is synthesised in the endothelium; of these, nitric oxide (NO), prostacyclin (PGI2) and endothelin (ET)-1 are the most important. There is a continuous basal release of NO determining the tone of peripheral blood vessels. Systemic inhibition of NO synthesis or scavenging of NO through oxidative stress causes an increase in arterial blood pressure. Also, the renin-angiotensin-aldosterone system has a major role in hypertension as it has a direct vasoconstrictor effect and important interactions with oxygen free radicals and NO. Prostacyclin, in contrast to NO, does not contribute to the maintenance of basal vascular tone of conduit arteries, but its effect on platelets is most important. ET acts as the natural counterpart to endothelium-derived NO and has an arterial blood pressure-raising effect in man. Anti-hypertensive therapy lowers blood pressure and may influence these different mediators, thus influencing endothelial function. In summary, due to its position between the blood pressure and smooth muscle cells responsible for peripheral resistance, the endothelium is thought to be both victim and offender in arterial hypertension. The delicate balance of endothelium-derived factors is disturbed in hypertension. Specific anti-hypertensive and anti-oxidant treatment is able to restore this balance.

Blunted heart rate response to upright tilt in people with Down syndrome

OBJECTIVES

To determine whether heart rate and blood pressure responses to upright tilt would be lower in subjects with Down syndrome (DS) than in control subjects with no disabilities.

DESIGN

Comparative study.

SETTING

University research laboratory.

PARTICIPANTS

Nineteen people with DS (mean age, 25.1+/-7.3 y) and 17 control subjects without disabilities (mean age, 28.4+/-5.6 y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Heart rate and blood pressure recordings were obtained at rest and during a 2-minute period of passive head up tilt to 80 degrees .

RESULTS

Heart rate and blood pressure increased significantly during the first 30 seconds of upright tilt in both groups ( P <.05) and then stabilized for the remainder of the test. The initial heart rate response to head up tilt (first 30s) was significantly higher in controls compared with subjects with DS ( P <.05), whereas the blood pressure response did not differ between groups ( P >.05). Controlling for heart rate reserve showed a blunted heart rate response through the tilt period in subjects with DS.

CONCLUSIONS

These data show a blunted heart rate response to upright tilt in people with DS, despite similar changes in blood pressure, consistent with reduced sympathoexcitation and possibly altered baroreceptor function in these people with DS.

Heart rate variability at rest and during exercise in persons with Down syndrome

OBJECTIVES

To determine whether autonomic dysfunction explains chronotropic incompetence observed in persons with Down syndrome (DS) and to measure heart rate variability (HRV) at rest and during exercise in persons with mental retardation with and without DS.

DESIGN

Comparative study.

SETTING

University exercise science laboratory.

PARTICIPANTS

Thirty-one subjects with mental retardation (age, 20.2 y) with DS (n=16; 10 men, 6 women) and without DS (n=15; 8 men, 7 women).

INTERVENTIONS

Not applicable. Main outcome measures HRV was determined at rest and at 2 steady-state exercise intensities on the treadmill in both time (standard deviation of the R-R interval, percentage of R-R intervals deviating by more than 50 ms from the previous R-R interval [deviation >50], square root of the mean squared differences of successive differences) and frequency (low-frequency power [LF]), high-frequency power [HF], the LF/HF ratio) domains.

RESULTS

The DS group demonstrated a statistically lower peak heart rate (161 beats/min vs 178 beats/min, P<.05), and peak oxygen consumption (27.4 mL.kg(-1).min(-1) vs 34.3 mL. kg(-1).min(-1), P<.05) than did the group with mental retardation without DS. At rest, all time domain measures of HRV and absolute HF power were significantly higher in the DS group (P<.05). Yet, LF power and LF/HF values did not differ between groups. All HRV variables decreased significantly at both exercise intensities, with no differences between groups during exercise (P<.05).

CONCLUSIONS

People with DS have greater parasympathetic activity at rest, but group differences disappear with the onset of exercise, which suggests that other variables are responsible for chronotropic incompetence in persons with DS.

Vascular basis of Alzheimer's pathogenesis

Considerable evidence now indicates that Alzheimer's disease (AD) is primarily a vascular disorder. This conclusion is supported by the following evidence: (1) epidemiologic studies linking vascular risk factors to cerebrovascular pathology that can set in motion metabolic, neurodegenerative, and cognitive changes in Alzheimer brains; (2) evidence that AD and vascular dementia (VaD) share many similar risk factors; (3) evidence that pharmacotherapy that improves cerebrovascular insufficiency also improves AD symptoms; (4) evidence that preclinical detection of potential AD is possible from direct or indirect regional cerebral perfusion measurements; (5) evidence of overlapping clinical symptoms in AD and VaD; (6) evidence of parallel cerebrovascular and neurodegenerative pathology in AD and VaD; (7) evidence that cerebral hypoperfusion can trigger hypometabolic, cognitive, and degenerative changes; and (8) evidence that AD clinical symptoms arise from cerebromicrovascular pathology. The collective data presented in this review strongly indicate that the present classification of AD is incorrect and should be changed to that of a vascular disorder. Such a change in classification would accelerate the development of better treatment targets, patient management, diagnosis, and prevention of this disorder by focusing on the root of the problem. In addition, a theoretical capsule summary is presented detailing how AD may develop from chronic cerebral hypoperfusion and the role of critically attained threshold of cerebral hypoperfusion (CATCH) and of vascular nitric oxide derived from endothelial nitric oxide synthase in triggering the cataclysmic cerebromicrovascular pathology.

Critically attained threshold of cerebral hypoperfusion: the CATCH hypothesis of Alzheimer's pathogenesis

This review discusses the experimental and clinical data which indicate that chronic cerebral hypoperfusion can affect metabolic, anatomic, and cognitive function adversely. In aged but not young animals, chronic brain hypoperfusion results in regional pre- and post-synaptic changes, protein synthesis abnormalities, energy metabolic dysregulation, reduced glucose utilization, cholinergic receptor loss, and visuo-spatial memory deficits. Additionally, aging animals that are kept for prolonged periods of time after chronic brain hypoperfusion, also develop brain capillary degeneration in CA1 hippocampus and neuronal damage extending from the hippocampal region to the temporo-parietal cortex where neurodegenerative tissue atrophy eventually forms. All these pathologic events occur in rodents in the absence of senile plaques and neurofibrillary tangles. Alzheimer brains reveal similar biochemical and structural changes as those experimentally induced in aging animals. Moreover, regional cerebral hypoperfusion is one of the earlier (if not the earliest) clinical manifestations in both the sporadic and familial forms of Alzheimer's disease. In addition, therapy that improves or increases cerebral perfusion is generally of some benefit to Alzheimer patients. Conversely, a variety of disorders with different etiologies that impair or diminish cerebral perfusion are reported to be risk factors for this dementia. These findings have prompted us to propose the concept that advanced aging in the presence of a vascular risk factor can converge to create a critically attained threshold of cerebral hypoperfusion (CATCH) that triggers regional brain microcirculatory disturbances and impairs optimal delivery of energy substrates needed for normal brain cell function. The outcome of this defect generates a chain of events leading to the progressive evolution of brain metabolic, cognitive and tissue pathology that characterize Alzheimer's disease. The possible role of CATCH in familial and early onset Alzheimer's disease is briefly discussed from a theoretical vantagepoint. The growing and most recent evidence in support of the CATCH concept is the focus of this review.

Amyloid beta-(1-40) stimulates cyclic GMP production via release of kinins in primary cultured endothelial cells

Increased beta-amyloid production is believed to play a central role in the pathogenesis of Alzheimer's disease. Amyloid is deposited not only in the brain of Alzheimer patients as senile plaques but also in the cerebral vessel wall leading to cerebral amyloid angiopathy. Freshly solubilised amyloid beta-(1-40) was previously reported to exert a vasoconstrictor effect. We investigated whether amyloid beta-(1-40) affects the nitric oxide (NO)/cyclic GMP pathway in primary cultured endothelial cells from bovine aorta and rat coronary microvessels. Surprisingly, a significant increase in cyclic GMP production after incubation with freshly dissolved amyloid beta-(1-40) was found. The stimulation of cyclic GMP production could be inhibited by the bradykinin B(2) receptor antagonist icatibant, the NO synthase inhibitor N-omega-nitro-L-arginine, the serine protease inhibitor 3, 4-dichloroisocoumarin and the selective plasma kallikrein inhibitor Pefabloc PK, suggesting activation of the plasma kallikrein-kinin system. This is supported by a three- to four-fold increase in kinins in the supernatant of both types of endothelial cells after incubation with amyloid beta-(1-40) at concentrations of 10(-7) and 10(-6) mol/l.