Differential effects of COMT on gait and executive control in aging

Right thalamic volume mediates impact of the dopamine beta-hydroxylase gene on the endowment effect

The endowment effect is a tendency that individuals overvalue items belonging to them relative to those items that do not. Previous studies showed a strong relation between the dopamine beta-hydroxylase (DBH) gene and the endowment effect (EE), and a link between EE and task-based functional MRI activation in multiple brain regions. However, the role of brain structure on EE remains unclear. In this study, we have explored whether regional brain volume mediate the effect of the DBH gene on EE. Results showed that rs1611115, single-nucleotide polymorphisms (SNPs) at DBH loci, were significantly associated with right thalamus volume and the endowment effect in males but not in female participants. Specifically, male DBH rs1611115 T-carriers had larger right thalamus volume compared to carriers of CC genotype and exhibited a greater endowment effect. Importantly, we found that right thalamus volume mediated the effect of rs1611115 on the endowment effect in male participants. This study demonstrated how thalamic volume plays an important mediating role between genetics and decision-making in humans.

Physical exercise, cognition, and brain health in aging

Exercise training is an important strategy to counteract cognitive and brain health decline during aging. Evidence from systematic reviews and meta-analyses supports the notion of beneficial effects of exercise in cognitively unimpaired and impaired older individuals. However, the effects are often modest, and likely influenced by moderators such as exercise training parameters, sample characteristics, outcome assessments, and control conditions. Here, we discuss evidence on the impact of exercise on cognitive and brain health outcomes in healthy aging and in individuals with or at risk for cognitive impairment and neurodegeneration. We also review neuroplastic adaptations in response to exercise and their potential neurobiological mechanisms. We conclude by highlighting goals for future studies, including addressing unexplored neurobiological mechanisms and the inclusion of under-represented populations.

The correlation between genetic factors and freezing of gait in patients with Parkinson's disease

BACKGROUND

Clinical-related risk factors to freezing of gait (FOG) in Parkinson's disease (PD) have been identified. Still, the influence of genetic variations on the FOG occurrence has been poorly studied thus far.

AIM

We aimed to evaluate the association of six selected polymorphisms of DRD2, ANKK1, and COMT genes with the FOG occurrence and explore the influence of ANNK1/DRD2 haplotypes on the onset of FOG in the group of PD patients.

METHOD

PD patients (n = 234), treated with levodopa for at least two years, were genotyped for the rs4680 in COMT, rs6277, rs1076560, and rs2283265 in DRD2, and rs1800497 and rs2734849 polymorphisms in ANKK1 genes. FOG was evaluated by posing a direct question. In addition, a comprehensive set of clinical scales was applied to all patients.

RESULTS

FOG occurred in 132 (56.4%) PD patients in our cohort. Freezers were younger at PD onset, had longer disease duration, used higher levodopa daily doses and dopaminergic agents, and had higher motor and non-motor scales scores than non-freezers. FOG was more frequent among AA rs4680 COMT carriers than AG and GG rs4680 COMT carriers. Independent predictors of FOG were: disease duration of more than ten years, levodopa daily dose higher than 500 mg/day, motor status, and COMT AA genotype. AGGAA and GGAAA haplotypes were revealed as protective and vulnerability factors for FOG occurrence.

CONCLUSION

In addition to previously identified disease- and therapy-related risk factors, our results suggested a possible contribution of dopamine-related genes to the FOG occurrence.

Effects of fundamental movement skills based dual-task and dance training on single- and dual-task walking performance in older women with dementia

OBJECTIVE

The purpose of this study was to compare the effects of fundamental movement skills (FMS)-based dual-task training and dance training on spatio-temporal characteristics of gait performance under single- and dual-task walking conditions among older women with dementia.

METHOD

Thirty-eight elderly females with dementia were randomly assigned to one of two groups: (1) dual-task intervention (DTI, age: 73 ± 6.5 years) or (2) Iranian dance intervention (IDI, age: 72.52 ± 6.01 years). Both groups participated in a 10-week intervention program (3 sessions per week, each lasting 50 min). Gait performance parameters (gait speed, cadence, and stride length) and dual-task costs (DTC) were examined using a gait analysis system. The participants completed three walking trials under two conditions: single- and dual-task. The video data was analyzed using motion analysis software (Frame-DIAS II, DKH, DKH Inc., Tokyo, Japan).

RESULTS

The results showed that both groups significantly improved in terms of all gait variables, and DTC decreased (p < .001) from pre- to post-test for both conditions. However, the main effects for the group and the group-by-time interactions were not significantly different between the two groups (p > .05).

CONCLUSION

These findings showed that DTI and IDI effectively improved gait performance following a 10-week intervention for older women with dementia. Therefore, it is suggested that either training program could decrease DTC and increase gait speed, stride length, and cadence among older females with dementia.

Data-driven approaches to executive function performance and structure in aging: Integrating person-centered analyses and machine learning risk prediction

Objective: Executive function (EF) performance and structure in nondemented aging are frequently examined with variable-centered approaches. Person-centered analytics can contribute unique information about classes of persons by simultaneously considering EF performance and structure. The risk predictors of these classes can then be determined by machine learning technology. Using data from the Victoria Longitudinal Study we examined two goals: (a) detect different underlying subgroups (or classes) of EF performance and structure and (b) test multiple risk predictors for best discrimination of these detected subgroups. Method: We used a classification sample (n = 778; M_age = 71.42) for the first goal and a prediction subsample (n = 570; M_age = 70.10) for the second goal. Eight neuropsychological measures represented three EF dimensions (inhibition, updating, shifting). Fifteen predictors represented five domains (genetic, functional, lifestyle, mobility, demographic). Results: First, we observed two distinct classes: (a) lower EF performance and unidimensional structure (Class 1) and (b) higher EF performance and multidimensional structure (Class 2). Second, Class 2 was predicted by younger age, more novel cognitive activity, more education, lower body mass index, lower pulse pressure, female sex, faster balance, and more physical activity. Conclusions: Data-driven modeling approaches tested the possibility of an EF aging class that displayed both preserved EF performance levels and sustained multidimensional structure. The two observed classes differed in both performance level (lower, higher) and structure (unidimensional, multidimensional). Machine learning prediction analyses showed that the higher performing and multidimensional class was associated with multiple brain health-related protective factors. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Catechol-O-methyltransferase (COMT) polymorphism predicts rapid gait speed changes in healthy older adults

IMPORTANCE

Adapting one's gait speed to external circumstances is critical for safe ambulation. Dopamine (DA), critical for adapting to increased task demands, predicts usual gait speed and may exert a greater role in complex tasks like rapid gait speed.

OBJECTIVE

We hypothesized that a genotypic proxy indicator of greater prefrontal DA signaling would predict significantly faster rapid gait.

DESIGN

Longitudinal cohort study over 8 years.

SETTING

Community-dwelling adults with no baseline mobility disability.

PARTICIPANTS

N = 2353 participants from the Health ABC Study.

MEASUREMENTS

Repeated measures of walking speed (meters/sec) were obtained in response to: "walk as fast as possible… (rapid gait) or "walk at your usual pace (usual gait)." Catechol-O-methyltransferase (COMT) val158met polymorphism indicated DA signaling (val/val = higher metabolism, lower DA signaling; met/met = lower metabolism, higher DA signaling).

RESULTS

Participants declined in rapid gait from 1.55 (SD = 0.33) to 1.35 m/s (SD = 0.34). Across the full follow-up period, the met/met genotype was associated with significantly greater rapid gait slowing. In mixed effect models, between-group differences were independent of covariates, and remained similar after adjustment for sensorimotor function, cognition, depressive symptoms, and energy. Follow-up analyses indicated the met/met genotype had a significantly faster rapid gait speed compared to the val/val genotype for the first 3 years (p < 0.01) but not years 4-8 (p > 0.05).

CONCLUSION

Greater prefrontal DA measured with COMT polymorphism may facilitate short-term adaptation to rapid walking demands that are lost over time. Studies should examine whether these effects are long-term and the underlying mechanistic pathways.

Sarcopenia and Neuroscience: Learning to Communicate

In the 1990s and early 2000s, the common definition for sarcopenia was age-related loss of skeletal muscle, and low levels of muscle mass were central to sarcopenia diagnosis. In more recent consensus definitions, however, low muscle strength displaces low muscle mass as a defining feature of sarcopenia. The change stems from growing evidence that muscle weakness is a better predictor of adverse health outcomes (e.g., mobility limitations) than muscle mass. This evidence accompanies an emerging recognition that central neural mechanisms are critical determinants of age-related changes in strength and mobility that can occur independently of variations in muscle mass. However, strikingly little practical attention is typically given to the potential role of the central nervous system in the aetiology or remediation of sarcopenia (i.e., low muscle function). In this article, we provide an overview of some mechanisms that mediate neural regulation of muscle contraction and control, and highlight the specific contributions of neural hypoexcitability, dopaminergic dysfunction, and degradation of functional and structural brain connectivity in relation to sarcopenia. We aim to enhance the lines of communication between the domains of sarcopenia and neuroscience. We believe that appreciation of the neural regulation of muscle contraction and control is fundamental to understanding sarcopenia and to developing targeted therapeutic strategies for its treatment.

Catechol-O-Methyltransferase Genotype, Frailty, and Gait Speed in a Biracial Cohort of Older Adults

OBJECTIVE

To examine whether the association between dopamine-related genotype and gait speed differs according to frailty status or race.

DESIGN

Cross-sectional population-based study (Cardiovascular Health Study).

SETTING

Multicenter study, four U.S. sites.

PARTICIPANTS

Volunteer community-dwelling adults aged 65 years and older, without evidence of Parkinson's disease (N = 3,744; 71 years; 82% White; 39% male).

MEASUREMENTS

Gait speed (usual pace; m/s), physical frailty (Fried definition), and genetic polymorphism of catechol-O-methyltransferase (COMT; rs4680), an enzyme regulating tonic brain dopamine levels, were assessed. Interaction of COMT by frailty and by race predicting gait speed were tested, and, if significant, analyses were stratified. Multivariable regression models of COMT predicting gait speed were adjusted for demographics and locomotor risk factors. Sensitivity analyses were repeated, stratified by clinical cutoffs of gait speed (0.6 and 1.0 m/s) instead of frailty status.

RESULTS

The interaction of COMT by frailty and COMT by race were P = .02 and P = .01, respectively. Compared with Met/Met (higher dopaminergic signaling), the Val/Val group (lower dopaminergic signaling) walked marginally more slowly in the full cohort (0.87 vs 0.89 m/s; P = .2). Gait speed differences were significant for frail (n = 220; 0.55 vs 0.63 m/s; P = .03), but not for prefrail (n = 1,691; 0.81 vs 0.81 m/s; P = .9) or nonfrail (n = 1,833; 0.98 vs 0.97 m/s; P = .7); results were similar in fully adjusted models. Among frail, associations were similar for Whites and Blacks, with statistical significance for Whites only. Associations stratified by clinical cutoffs of gait speed were not significant.

CONCLUSION

The association of dopamine-related genotype with gait speed is stronger among adults with frailty compared with those without frailty. The potential effects of dopaminergic signaling on preserving physical function in biracial cohorts of frail adults should be further examined.

Influence of Striatal Dopamine, Cerebral Small Vessel Disease, and Other Risk Factors on Age-Related Parkinsonian Motor Signs

OBJECTIVE

Parkinsonian motor signs are common and disabling in older adults without Parkinson's disease (PD), but its risk factors are not completely understood. We assessed the influence of striatal dopamine levels, cerebral small vessel disease, and other factors on age-related parkinsonian motor signs in non-PD adults.

METHODS

Striatal dopamine transporter (DAT) binding was quantified via [11C]-CFT positron emission tomography in 87 neurologically intact adults (20-85 years, 57.47% female) with concurrent data on: Unified Parkinson's Disease Rating Scale motor (UPDRSm), white matter hyperintensities (WMH), and other risk factors (grip strength, vibratory sensitivity, cardio- and cerebro-vascular comorbidities). Sex-adjusted nonparametric models first estimated the associations of age, DAT, WMH, and other factors with UPDRSm; next, interactions of age by DAT, WMH, or other factors were tested. To quantify the influence of DAT, WMH, and other risk factors on the main association of age with UPDRSm, multivariable mediation models with bootstrapped confidence intervals (CI) were used.

RESULTS

Older age, lower DAT, higher WMH, and worse risk factors significantly predicted worse UPDRSm (sex-adjusted p < .04 for all). DAT, but not WMH or other factors, positively and significantly interacted with age (p = .02). DAT significantly reduced the age-UPDRSm association by 30% (results of fully adjusted mediation model: indirect effect: 0.027; bootstrapped 95% CI: 0.0007, 0.074).

CONCLUSIONS

Striatal dopamine appears to influence to some extent the relationship between age and parkinsonian signs. However, much of the variance of parkinsonian signs appears unexplained. Longitudinal studies to elucidate the multifactorial causes of this common condition of older age are warranted.

Is impaired dopaminergic function associated with mobility capacity in older adults?

The capacity to move is essential for independence and declines with age. Slow movement speed, in particular, is strongly associated with negative health outcomes. Prior research on mobility (herein defined as movement slowness) and aging has largely focused on musculoskeletal mechanisms and processes. More recent work has provided growing evidence for a significant role of the nervous system in contributing to reduced mobility in older adults. In this article, we report four pieces of complementary evidence from behavioral, genetic, and neuroimaging experiments that, we believe, provide theoretical support for the assertion that the basal ganglia and its dopaminergic function are responsible, in part, for age-related reductions in mobility. We report four a posteriori findings from an existing dataset: (1) slower central activation of ballistic force development is associated with worse mobility among older adults; (2) older adults with the Val/Met intermediate catecholamine-O-methyl-transferase (COMT) genotype involved in dopamine degradation exhibit greater mobility than their homozygous counterparts; (3) there are moderate relationships between performance times from a series of lower and upper extremity tasks supporting the notion that movement speed in older adults is a trait-like attribute; and (4) there is a relationship of functional connectivity within the medial orbofrontal (mOFC) cortico-striatal network and measures of mobility, suggesting that a potential neural mechanism for impaired mobility with aging is the deterioration of the integrity of key regions within the mOFC cortico-striatal network. These findings align with recent basic and clinical science work suggesting that the basal ganglia and its dopaminergic function are mechanistically linked to age-related reductions in mobility capacity.

Interaction of Catechol-O-methyltransferase Val158 Met polymorphism and sex influences association of parietal intrinsic functional connectivity and immediate verbal memory

INTRODUCTION

Sex differences modulate catechol-O-methyltransferase (COMT) genotype effect at a synaptic dopamine level, which influences brain function as well as cognitive performance. In this study, we investigated how COMT Val¹⁵⁸ Met polymorphism and sex affect intrinsic functional connectivity and memory.

METHODS

Intrinsic functional networks were extracted using independent component analysis of resting-state functional magnetic resonance imaging data from 186 healthy young COMT-genotyped participants. The association of these functional networks and memory function was tested to investigate whether the effect of COMT × sex interaction influences the association of intrinsic functional connectivity and memory performance. Quadratic curve fit estimation was used to examine the relationship between functional connectivity and speculative dopamine level among groups.

RESULTS

COMT MM/MV carriers, relative to VV carriers, showed increased functional connectivity in left superior parietal lobule and right inferior frontal gyrus. Further, male MM/MV carriers showed significant higher mean functional connectivity in left inferior parietal lobule relative to male VV carriers and female MM/MV carriers, which was associated with worse immediate verbal recall performance. Additionally, the relationship between inferior parietal lobule functional connectivity and speculative dopamine level among groups fits the quadratic curve.

CONCLUSIONS

These findings suggest that the interaction of COMT genotype and sex might regulate synaptic dopaminergic concentrations and influence the association of intrinsic functional connectivity and immediate verbal memory in left inferior parietal lobule.

Genetic polymorphisms for BDNF, COMT, and APOE do not affect gait or ankle motor control in chronic stroke: A preliminary cross-sectional study

Background: Motor deficits after stroke are a primary cause of long-term disability. The extent of functional recovery may be influenced by genetic polymorphisms. Objectives: Determine the effect of genetic polymorphisms for brain-derived neurotrophic factor (BDNF), catechol-O-methyltransferase (COMT), and apolipoprotein E (APOE) on walking speed, walking symmetry, and ankle motor control in individuals with chronic stroke. Methods: 38 participants with chronic stroke were compared based upon genetic polymorphisms for BDNF (presence [MET group] or absence [VAL group] of a Met allele), COMT (presence [MET group] or absence [VAL group] of a Met allele), and APOE (presence [ε4+ group] of absence [ε4- group] of ε4 allele). Comfortable and maximal walking speed were measured with the 10-m walk test. Gait spatiotemporal symmetry was measured with the GAITRite electronic mat; symmetry ratios were calculated for step length, step time, swing time, and stance time. Ankle motor control was measured as the accuracy of performing an ankle tracking task. Results: No significant differences were detected (p ≥ 0.11) between the BDNF, COMT, or APOE groups for any variables. Conclusions: In these preliminary findings, genetic polymorphisms for BDNF, COMT, and APOE do not appear to affect walking speed, walking symmetry, or ankle motor performance in chronic stroke.

Measuring gait speed to better identify prodromal dementia

Slow gait speed has been shown to predict incident dementia and cognitive decline in older individuals. We aimed to summarize the evidence concerning the association of slow gait speed with cognitive decline and dementia, and discuss the possible shared pathways leading to cognitive and motor impairments, under the unifying hypothesis that body and mind are intimately connected. This is a scoping review supported by a systematic search of the literature, performed on PubMed and Web of Science. Longitudinal studies providing information on the role of gait speed in the prediction of cognitive decline and dementia in cognitively intact people and in those with initial cognitive impairment were eligible. Of 39 studies selected, including overall 57,456 participants, 33 reported a significant association between gait speed and cognitive outcomes, including dementia. Neurodegenerative pathology and cerebrovascular burden may damage cerebral areas involved in both cognitive functions and motor control. At the same time, systemic conditions, characterized by higher cardiorespiratory, and metabolic and inflammatory burden, can affect a number of organs and systems involved in motor functions, including the brain, having ultimately an impact on cognition. The interplay of body and mind seems relevant during the development of cognitive decline and dementia. The measurement of gait speed may improve the detection of prodromal dementia and cognitive impairment in individuals with and without initial cognitive deficits. The potential applicability of such a measure in both clinical and research settings points at the importance of expanding our knowledge about the common underlying mechanisms of cognitive and motor decline.

Genetic markers of dopaminergic transmission predict performance for older males but not females

Mobility and memory declines with aging can limit independence. Several single-nucleotide polymorphisms have been associated with cognitive performance, but studies investigating motor function are scant. We examined 4 single-nucleotide polymorphisms involved in dopaminergic metabolism: BDNF (Val66Met), DRD3 (Ser9Gly), DBH (C>T), and COMT (Val158Met) for their relationship to motor and cognitive function in healthy older adults (n = 4605 and n = 7331) who participated in the U.S. Health and Retirement Study. Individuals with genotypes associated with reduced dopamine metabolism exhibited poorer balance and memory. We found the most pronounced effects in the oldest participants (aged 85+ years), supporting the notion that age-related declines in dopamine availability contribute to magnified genotype effects with advancing age. Moreover, males demonstrated stronger associations than did females between a number of beneficial dopamine alleles and cognitive scores, suggesting that sex differences in dopaminergic transmission interact with genotype to influence performance. These findings point to common genetic variants related to dopaminergic metabolism that characterizes individual differences in motor and cognitive function in older adults.

Vascular and dopaminergic contributors to mild parkinsonian signs in older adults

OBJECTIVE

Mild parkinsonian signs (MPS) are an underappreciated neurologic condition in older adults; we assessed associations of MPS with measures of dopaminergic (catechol-O-methyltransferase [COMT] genotype, an indicator of synaptic dopamine levels) and vascular (white matter hyperintensities [WMH], an indicator of cerebral small vessel disease) factors.

METHODS

In a cohort of older adults (mean age 82.6 years [SD 2.6]; 58.0% female; 38.8% black), we assessed cross-sectional associations of WMH volume and COMT Val158Met (rs4680) genotype (n = 35 Met/Met, n = 180 Val carriers) with MPS by regression models adjusted for demographic and health characteristics. Interactions between WMH and COMT were assessed and analyses were repeated stratified by COMT genotype (Met/Met related to higher synaptic dopamine vs Val carriers related to lower synaptic dopamine).

RESULTS

MPS was present in 42.3% of our sample. WMH (odds ratio [OR] 1.16, confidence interval [CI] 1.05-1.27) but not COMT (Met/Met compared to Val carrier: OR 0.62, CI 0.27-1.42) was related to MPS. There was a significant interaction between WMH and COMT (p = 0.03). Stratified analyses reveled a strong association between WMH and MPS among COMT Val carriers (OR 1.23, CI 1.09-1.38), but not for Met/Met (OR 0.68, CI 0.45-1.02), independent of covariates.

CONCLUSIONS

WMH had a direct relation with MPS. In contrast, COMT was not associated with MPS, but it did modify the effect of WMH on MPS. The dopaminergic system may provide compensation for the effects of WMH on MPS. These findings suggest that MPS has a vascular rather than dopaminergic origin in older adults, but both factors are important in MPS manifestation.

Dopaminergic polymorphisms associated with medication responsiveness of gait in Parkinson's disease

BACKGROUND

Gait dysfunction is a common symptom of Parkinson's disease that can cause significant disability and put patients at risk for falls. These symptoms show variable responsiveness to dopaminergic therapy.

OBJECTIVE

To determine whether dopaminergic (rs1076560 DRD2 G > T and rs4680 catechole-o-methyltranspherase (COMT) Val158Met) or brain derived neurotrophic factor (rs6265 BDNF Val66Met) genetic polymorphisms are associated with gait function and medication responsiveness in Parkinson's disease.

METHOD

Gait function was evaluated on two days for patients (ON and OFF medication in a counterbalanced fashion) and a single session for controls. Investigators were blinded to genotype during data collection. Associations between genotype and medication responsiveness were analyzed using mixed model ANOVAs. A priori hypotheses were tested using GAITRite^® electronic mat spatiotemporal gait parameters including step length, step width, velocity, portion of double and single support per gait cycle, and variability of these measures ON and OFF medication.

RESULTS

We found that the DRD2 polymorphism, but neither COMT nor BDNF, was consistently associated with gait function and medication responsiveness in the patients. Specifically, Parkinson's disease patients with reduced striatal D2 expression (DRD2 T allele carriers) had worse gait dysfunction and showed greater dopamine responsiveness of gait function compared to patients who were homozygous for the G allele. There was no effect of any of the genetic polymorphisms on gait for controls.

CONCLUSIONS AND RELEVANCE

The findings suggest that genetic subgrouping, in particular for DRD2, may be used to identify Parkinson's disease patient subgroups that are more dopamine responsive for gait function.

Association of Family History of Exceptional Longevity With Decline in Physical Function in Aging

Background

Although many genetic and nongenetic factors interact to determine an individual's physical phenotype, there has been limited examination of the contribution of family history of exceptional parental longevity on decline in physical function in aging.

Methods

The LonGenity study recruited a relatively genetically homogenous cohort of Ashkenazi Jewish adults age 65 and older, who were defined as either offspring of parents with exceptional longevity ([OPEL]: having at least one parent who lived to age 95 or older) or offspring of parents with usual survival ([OPUS]: neither parent survived to age 95). Decline in performance on objective measures of strength (grip strength), balance (unipedal stance), and mobility (gait speed) as well as a composite physical function measure, the Short physical performance battery (SPPB), were compared between the two groups over a median follow-up of 3.2 years, accounting for age, sex, education, and comorbidities.

Results

Of the 984 LonGenity participants (mean age 76, 55% women), 448 were OPEL and 536 were OPUS. Compared to OPUS, OPEL had slower decline on measures of unipedal stance (-0.03 log-units/year, p = .026), repeated chair rise (0.13 s/year, p = .020) and SPPB (-0.11 points/year, p = .002). OPEL women had slower decline on chair rise and SPPB scores compared to OPUS women, although OPEL men had slower decline on unipedal stance compared to OPUS men.

Conclusion

Our findings provide evidence that variation in late-life decline in physical function is associated with familial longevity, and may vary for men and women.

Catechol-O-Methyltransferase Genotype and Gait Speed Changes over 10 Years in Older Adults

OBJECTIVES

To determine the association between catechol-O-methyltransferase (COMT) genotype and 6-m walk time and to determine whether these associations are quadratic in nature, similar to previously reported U-shaped associations between dopamine and gait and cognition.

DESIGN

Prospective cohort study.

SETTING

Health, Aging and Body Composition Study.

PARTICIPANTS

Black (n = 850) and white (n = 1,352) men and women with a mean age of 73.5 ± 2.85 at baseline.

MEASUREMENTS

Mixed models were used to assess the association between the COMT genotype and 6-m walk time, cross-sectionally and longitudinally over 10 years. Models were assessed unstratified and stratified according to race because allele distributions were different between white and black participants.

RESULTS

There was a significant U-shaped association between COMT genotype and 6-m walk time: those with higher (Val/Val) and lower (Met/Met) dopamine slowed more over 10 years (0.22 ± 0.02 seconds per visit and 0.23 ± 0.02 seconds per visit, respectively) than those with the intermediate (Met/Val) dopamine (0.20 ± 0.02 seconds per visit) (P = .005). Stratified results showed a significant relationship in black (P = .01) but not white (P = .15) participants.

CONCLUSION

These findings indicate a role of dopaminergic regulation of gait speed in community-dwelling older adults and of prefrontal cortex involvement in gait performance. Future work should investigate the molecular integrity of dopaminergic networks and gait changes over time and structural changes in the brain with COMT and gait decline in older adults.

The complex genetics of gait speed: genome-wide meta-analysis approach

Emerging evidence suggests that the basis for variation in late-life mobility is attributable, in part, to genetic factors, which may become increasingly important with age. Our objective was to systematically assess the contribution of genetic variation to gait speed in older individuals. We conducted a meta-analysis of gait speed GWASs in 31,478 older adults from 17 cohorts of the CHARGE consortium, and validated our results in 2,588 older adults from 4 independent studies. We followed our initial discoveries with network and eQTL analysis of candidate signals in tissues. The meta-analysis resulted in a list of 536 suggestive genome wide significant SNPs in or near 69 genes. Further interrogation with Pathway Analysis placed gait speed as a polygenic complex trait in five major networks. Subsequent eQTL analysis revealed several SNPs significantly associated with the expression of PRSS16, WDSUB1 and PTPRT, which in addition to the meta-analysis and pathway suggested that genetic effects on gait speed may occur through synaptic function and neuronal development pathways. No genome-wide significant signals for gait speed were identified from this moderately large sample of older adults, suggesting that more refined physical function phenotypes will be needed to identify the genetic basis of gait speed in aging.

Cortisol Awakening Response and Walking Speed in Older People

In older people, less diurnal variability in cortisol levels has been consistently related to worse physical performance, especially to slower walking speed (WS). The cortisol awakening response (CAR) is a discrete component of the hypothalamic-pituitary-adrenal axis that has been related to several health problems, such as cardiovascular disease and/or worse performance on executive function and memory. The relationship between the CAR and physical performance in older people is poorly understood. In this study, in 86 older people (mean age = 64.42, SD = 3.93), we investigated the relationship between the CAR and WS, a commonly used measure of physical performance in the older population that has also been related to health problems, such as cardiovascular disease and executive function performance in older people. Additionally, we studied whether the relationship between the CAR and WS was independent from cortisol levels on awakening and several possible confounders. Results showed that a CAR of reduced magnitude (measured with 3 samples each day, for two consecutive days, and calculated as the area under the curve with respect to the increase), but not cortisol levels on awakening, was related to slower WS. In addition, this relationship was independent from cortisol levels on awakening. It is possible that a CAR of reduced magnitude would contribute to less diurnal cortisol variability, affecting physical performance. Additionally, it is possible that a CAR of reduced magnitude affects WS through a possible negative effect on executive function, or that the association between the CAR and WS is due to the fact that both are related to similar health problems and to changes in cognitive performance in older people.

Online fronto-cortical control of simple and attention-demanding locomotion in humans

Knowledge of online functional brain mechanisms of locomotion is scarce due to technical limitations of traditional neuroimaging methods. Using functional Near Infrared Spectroscopy (fNIRS) we evaluated task-related changes in oxygenated hemoglobin levels (HbO2) in real-time over the pre-frontal-cortex (PFC) regions during simple (Normal Walk; NW) and attention-demanding (Walking While Talking; WWT) locomotion tasks in a large cohort of non-demented older adults. Results revealed that the assessment of task-related changes in HbO2 was internally consistent. Imposing greater demands on the attention system during locomotion resulted in robust bilateral PFC increases in HbO2 levels during WWT compared to NW and the cognitive interference tasks. Elevated PFC oxygenation levels were maintained throughout the course of WWT but not during the NW condition. Increased oxygenation levels in the PFC were related to greater stride length and better cognitive performance but not to faster gait velocity in WWT. These findings elucidate online brain mechanisms of locomotion, and confer significant implications for risk assessment and intervention for major mobility outcomes.

At the interface of sensory and motor dysfunctions and Alzheimer's disease

Recent evidence indicates that sensory and motor changes may precede the cognitive symptoms of Alzheimer's disease (AD) by several years and may signify increased risk of developing AD. Traditionally, sensory and motor dysfunctions in aging and AD have been studied separately. To ascertain the evidence supporting the relationship between age-related changes in sensory and motor systems and the development of AD and to facilitate communication between several disciplines, the National Institute on Aging held an exploratory workshop titled "Sensory and Motor Dysfunctions in Aging and AD." The scientific sessions of the workshop focused on age-related and neuropathologic changes in the olfactory, visual, auditory, and motor systems, followed by extensive discussion and hypothesis generation related to the possible links among sensory, cognitive, and motor domains in aging and AD. Based on the data presented and discussed at this workshop, it is clear that sensory and motor regions of the central nervous system are affected by AD pathology and that interventions targeting amelioration of sensory-motor deficits in AD may enhance patient function as AD progresses.

What can biomarkers tell us about cognition in Parkinson's disease?

Cognitive decline is common in Parkinson's disease (PD), even in the early motor stage, and this non-motor feature impacts quality of life and prognosis tremendously. In this article, we discuss marker candidates for cognitive decline in PD from different angles, including functional and structural imaging techniques, biological fluid markers in cerebrospinal fluid, and blood genetic predictors, as well as gait as a surrogate marker of cognitive decline. Specifically, imaging-based markers of cognitive impairment in PD include cortical atrophy, reduced cortical metabolism, loss of cortical cholinergic and frontal dopaminergic function, as well as an increased cortical amyloid load. Reduced β-amyloid(1-42) in cerebrospinal fluid and lower plasma levels of epidermal growth factor are predictors for cognitive decline in PD. In addition, genetic variation in the apolipoprotein E (APOE), catechol-O-methyltransferase (COMT), microtubule-associated protein tau (MAPT), and glucocerebrosidase (GBA) genes may confer risk for cognitive impairment in PD; and gait disturbance may also indicate an increased risk for dementia. Other marker candidates have been proposed and are discussed. All of the current studies are hampered by gaps in our knowledge about the molecular causes of cognitive decline, which will have to be considered in future biomarker studies.

Association of exceptional parental longevity and physical function in aging

Offspring of parents with exceptional longevity (OPEL), who are more likely to carry longevity-associated genotypes, may age more successfully than offspring of parents with usual survival (OPUS). Maintenance of physical function is a key attribute of successful aging. While many genetic and non-genetic factors interact to determine physical phenotype in aging, examination of the contribution of exceptional parental longevity to physical function in aging is limited. The LonGenity study recruited a relatively genetically homogenous cohort of Ashkenazi Jewish (AJ) adults age 65 and older, who were defined as either OPEL (having at least one parent who lived to age 95 or older) or OPUS (neither parent survived to age 95). Subjective and objective measures of physical function were compared between the two groups, accounting for potential confounders. Of the 893 LonGenity subjects, 365 were OPEL and 528 were OPUS. OPEL had better objective and subjective measures of physical function than OPUS, especially on unipedal stance (p = 0.009) and gait speed (p = 0.002). Results support the protective role of exceptional parental longevity in preventing decline in physical function, possibly via genetic mechanisms that should be further explored.

Catechol-O-methyltransferase Val158Met polymorphism modulates gray matter volume and functional connectivity of the default mode network

The effect of catechol-O-methyltransferase (COMT) Val158Met polymorphism on brain structure and function has been previously investigated separately and regionally; this prevents us from obtaining a full picture of the effect of this gene variant. Additionally, gender difference must not be overlooked because estrogen exerts an interfering effect on COMT activity. We examined 323 young healthy Chinese Han subjects and analyzed the gray matter volume (GMV) differences between Val/Val individuals and Met carriers in a voxel-wise manner throughout the whole brain. We were interested in genotype effects and genotype × gender interactions. We then extracted these brain regions with GMV differences as seeds to compute resting-state functional connectivity (rsFC) with the rest of the brain; we also tested the genotypic differences and gender interactions in the rsFCs. Val/Val individuals showed decreased GMV in the posterior cingulate cortex (PCC) compared with Met carriers; decreased GMV in the medial superior frontal gyrus (mSFG) was found only in male Val/Val subjects. The rsFC analysis revealed that both the PCC and mSFG were functionally correlated with brain regions of the default mode network (DMN). Both of these regions showed decreased rsFCs with different parts of the frontopolar cortex of the DMN in Val/Val individuals than Met carriers. Our findings suggest that the COMT Val158Met polymorphism modulates both the structure and functional connectivity within the DMN and that gender interactions should be considered in studies of the effect of this genetic variant, especially those involving prefrontal morphology.

Estrogen pathway polymorphisms in relation to primary open angle glaucoma: an analysis accounting for gender from the United States

PURPOSE

Circulating estrogen levels are relevant in glaucoma phenotypic traits. We assessed the association between an estrogen metabolism single nucleotide polymorphism (SNP) panel in relation to primary open angle glaucoma (POAG), accounting for gender.

METHODS

We included 3,108 POAG cases and 3,430 controls of both genders from the Glaucoma Genes and Environment (GLAUGEN) study and the National Eye Institute Glaucoma Human Genetics Collaboration (NEIGHBOR) consortium genotyped on the Illumina 660W-Quad platform. We assessed the relation between the SNP panels representative of estrogen metabolism and POAG using pathway- and gene-based approaches with the Pathway Analysis by Randomization Incorporating Structure (PARIS) software. PARIS executes a permutation algorithm to assess statistical significance relative to the pathways and genes of comparable genetic architecture. These analyses were performed using the meta-analyzed results from the GLAUGEN and NEIGHBOR data sets. We evaluated POAG overall as well as two subtypes of POAG defined as intraocular pressure (IOP) ≥22 mmHg (high-pressure glaucoma [HPG]) or IOP <22 mmHg (normal pressure glaucoma [NPG]) at diagnosis. We conducted these analyses for each gender separately and then jointly in men and women.

RESULTS

Among women, the estrogen SNP pathway was associated with POAG overall (permuted p=0.006) and HPG (permuted p<0.001) but not NPG (permuted p=0.09). Interestingly, there was no relation between the estrogen SNP pathway and POAG when men were considered alone (permuted p>0.99). Among women, gene-based analyses revealed that the catechol-O-methyltransferase gene showed strong associations with HTG (permuted gene p≤0.001) and NPG (permuted gene p=0.01).

CONCLUSIONS

The estrogen SNP pathway was associated with POAG among women.

Aging, the central nervous system, and mobility

BACKGROUND

Mobility limitations are common and hazardous in community-dwelling older adults but are largely understudied, particularly regarding the role of the central nervous system (CNS). This has limited development of clearly defined pathophysiology, clinical terminology, and effective treatments. Understanding how changes in the CNS contribute to mobility limitations has the potential to inform future intervention studies.

METHODS

A conference series was launched at the 2012 conference of the Gerontological Society of America in collaboration with the National Institute on Aging and the University of Pittsburgh. The overarching goal of the conference series is to facilitate the translation of research results into interventions that improve mobility for older adults.

RESULTS

Evidence from basic, clinical, and epidemiological studies supports the CNS as an important contributor to mobility limitations in older adults without overt neurologic disease. Three main goals for future work that emerged were as follows: (a) develop models of mobility limitations in older adults that differentiate aging from disease-related processes and that fully integrate CNS with musculoskeletal contributors; (b) quantify the contribution of the CNS to mobility loss in older adults in the absence of overt neurologic diseases; (c) promote cross-disciplinary collaboration to generate new ideas and address current methodological issues and barriers, including real-world mobility measures and life-course approaches.

CONCLUSIONS

In addition to greater cross-disciplinary research, there is a need for new approaches to training clinicians and investigators, which integrate concepts and methodologies from individual disciplines, focus on emerging methodologies, and prepare investigators to assess complex, multisystem associations.

The protective effects of executive functions and episodic memory on gait speed decline in aging defined in the context of cognitive reserve

OBJECTIVES

To evaluate whether levels of cognitive reserve (CR), as measured using the Wechsler Adult Intelligence Scale (WAIS)-III vocabulary test, moderated longitudinal associations between cognitive functions and decline in gait speed in a community-based cohort of older adults without dementia, specifically, whether the protective effect of executive function (EF) and episodic memory against decline in gait speed would be greater in individuals with higher CR.

DESIGN

Longitudinal (median number of repeated annual gait speed measures, 3; maximum number of visits, 7).

SETTING

General community.

PARTICIPANTS

Seven hundred thirty-one community-residing individuals aged 70 and older without dementia were followed longitudinally with cognitive and gait evaluations at baseline and at annual visits.

MEASUREMENTS

Decline in gait speed (cm/s) served as the primary outcome. The Free and Cued Selective Reminding Test (FCSRT) was used to assess episodic memory. The Digit Symbol Substitution Test (DSST) was used to assess attention and EF. The vocabulary test served as a marker for CR.

RESULTS

Linear mixed effects model showed that gait speed declined over the follow-up period (P < .001). The significant three-way interactions of time by DSST by vocabulary (P = .01) and time by FCSRT by vocabulary (P = .02) revealed that levels of CR moderated the longitudinal associations between EF and episodic memory and gait speed decline.

CONCLUSION

The protective effects of EF and episodic memory against gait speed decline in aging are greater in individuals with higher CR.

Depressive symptoms and gait dysfunction in the elderly

OBJECTIVE

Assess the association between depressive symptoms (not meeting the criteria for major depression) and gait dysfunction in older adults.

DESIGN

Cross-sectional study.

SETTING

Einstein Aging Study, a community-based longitudinal aging study.

PARTICIPANTS

Six hundred ten nondemented and nondepressed community-residing adults age 70 and older.

MEASUREMENTS

Depressive symptoms measured using the 15-item Geriatric Depression Scale. To obtain a comprehensive assessment of gait, eight individual quantitative gait parameters were assessed: velocity (cm/s), stride length (cm), cadence (steps/min), swing phase (seconds), stance phase (seconds), double support phase (seconds), stride length variability (SD of stride length), and swing time variability (SD of swing time). Multiple linear regression analysis was applied to study the association of depressive symptoms with gait, adjusting for potential confounders including demographic variables, medical illnesses, and clinical gait abnormalities.

RESULTS

Increased level of depressive symptoms was associated with worse velocity, stride, and swing time variability. The relationship of the remaining five gait variables with depressive symptoms was not significant in the fully adjusted models.

CONCLUSIONS

Higher levels of depressive symptoms are associated with worse performance in specific quantitative gait variables in community-residing older adults.

The relationship between attention and gait in aging: facts and fallacies

The current study critically assessed the relationship between cognitive functions and gait in nondemented older adults. Quantitative measures of gait (velocity, cadence, and a coefficient of variance in stride length) were assessed in single and dual-task conditions. Three cognitive factors captured the domains of Executive Attention, Verbal IQ, and Memory. Linear regressions showed that Executive Attention was related to velocity in both walking conditions. However, Memory and Verbal IQ were also related to velocity. Memory was related to Cadence in both walking conditions. Executive Attention was related to the coefficient of variance in stride length in both walking conditions. Linear mixed effects models showed that dual-task costs were largest in velocity followed by cadence and the coefficient of variance in stride length. The relationship between cognitive functions and gait depends, in part, on the analytic approach used, gait parameters assessed, and walking condition.

Upper and lower extremity motor function and cognitive impairment in multiple sclerosis

Motor impairments and cognitive dysfunction are common in multiple sclerosis (MS). We aimed to delineate the relationship between cognitive capacity and upper and lower motor function in 211 MS patients, and 120 healthy volunteers. Lower and upper motor function were assessed with the Timed 25 Foot Walk (T25FW) and the Nine Hole Peg Test (NHPT) as implemented in the Multiple Sclerosis Functional Composite (MSFC). Subjects also underwent neuropsychological evaluation. Hierarchical linear regression analysis was conducted separately for the MS and healthy groups with the T25FW and NHPT serving as the outcome measures. Cognitive performance indices served as predictors. As expected, healthy subjects performed better than the MS group on all measures. Processing speed and executive function tests were significant predictors of lower and upper motor function in both groups. Correlations were more robust in the MS group, where cognitive tests predicted variability in motor function after controlling for disease duration and physical disability. In conclusion, we find evidence of higher order cognitive control of motor function that appears to be particularly salient in this large and representative MS sample. The findings may have implications for risk assessment and treatment of mobility dysfunction in MS.

Entacapone promotes cAMP-dependent colonic Cl(-) secretion in rats

BACKGROUND

Entacapone is a promising drug used widely for the treatment of Parkinson's disease (PD) as a catechol-O-methyl transferase (COMT) inhibitor. However, entacapone has gastrointestinal side effects. The aim of this study was to investigate the effects of entacapone on the epithelial ion transport in rat distal colon, and explore the underlying mechanism.

METHODS

The study was performed on freshly isolated colonic mucosa-only, submucosa-only and mucosa-submucosa preparations in rat. The short circuit current (I(SC) ) was measured to determine electrogenic ion transport, and a scanning ion-selective electrode technique (SIET) was used to directly measure Cl(-) flux across the epithelium. The content of intracellular cAMP was measured with radioimmunoassay (RIA).

KEY RESULTS

Entacapone increased mucosal I(SC) in the rat distal colon. I(SC) was inhibited significantly by apical addition of diphenylamine-2,2'-dicarboxylic acid (DPC), a blocker of the Cl(-) channel, basolateral application of bumetanide, an inhibitor of Na(+) -K(+) -2Cl(-) co-transporter (NKCC), removal of Cl(-) from the bathing solution, and pretreatment with MDL 12330A, an inhibitor of adenylate cyclase. Inhibiting endogenous prostaglandin (PG) synthesis with indomethacin, and eliminating submucosal enteric neural activity with tetrodotoxin (TTX)-inhibited entacapone-evoked I(SC) increases. Similar results were also obtained when Cl(-) flux was measured with SIET. Entacapone significantly increased intracellular cAMP content, which was greatly inhibited by either indomethacin or TTX in the tissues containing submucosal plexus, and by only indomethacin in the mucosa-only preparations.

CONCLUSIONS & INFERENCES

Entacapone stimulates cAMP-dependent Cl(-) secretion in the rat colon, and this process is regulated by endogenous PG and the submucosal enteric nervous system.

fNIRS study of walking and walking while talking in young and old individuals

BACKGROUND

Evidence suggests that gait is influenced by higher order cognitive and cortical control mechanisms. However, less is known about the functional correlates of cortical control of gait.

METHODS

Using functional near-infrared spectroscopy, the current study was designed to evaluate whether increased activations in the prefrontal cortex (PFC) were detected in walking while talking (WWT) compared with normal pace walking (NW) in 11 young and 11 old participants. Specifically, the following two hypotheses were evaluated: (a) Activation in the PFC would be increased in WWT compared with NW. (b) The increase in activation in the PFC during WWT as compared with NW would be greater in young than in old participants.

RESULTS

Separate linear mixed effects models with age as the two-level between-subject factor, walking condition (NW vs WWT) as the two-level repeated within-subject factor, and HbO2 levels in each of the 16 functional near-infrared spectroscopy channels as the dependent measure revealed significant task effects in 14 channels, indicating a robust bilateral increased activation in the PFC in WWT compared with NW. Furthermore, the group-by-task interaction was significant in 11 channels with young participants showing greater WWT-related increase in HbO2 levels compared with the old participants.

CONCLUSIONS

This study provided the first evidence that oxygenation levels are increased in the PFC during WWT compared with NW in young and old individuals. This effect was modified by age suggesting that older adults may under-utilize the PFC in attention-demanding locomotion tasks.

Hemispheric specialization during mental imagery of brisk walking

OBJECTIVES

Brisk walking, a sensitive test to evaluate gait capacity in normal and pathological aging such as parkinsonism, is used as an alternative to classical fitness program for motor rehabilitation and may help to decrease the risk of cognitive deterioration observed with aging. In this study, we aimed to identify brain areas normally involved in its control.

METHODS

We conducted a block-design blood oxygen level dependent function magnetic resonance imaging (BOLD fMRI) experiment in 18 young healthy individuals trained to imagine themselves in three main situations: brisk walking in a 25-m-long corridor, standing or lying. Imagined walking time (IWT) was measured as a control of behavioral performance during fMRI.

RESULTS

The group mean IWT was not significantly different from the actual walking time measured during a training session prior to the fMRI study. Compared with other experimental conditions, mental imagery (MI) of brisk walking was associated with stronger activity in frontal and parietal regions mainly on the right, and cerebellar hemispheres, mainly on the left. Presumed imagined walking speed (2.3 ± 0.4 m/s) was positively correlated with activity levels in the right dorsolateral prefrontal cortex and posterior parietal lobule along with the vermis and the left cerebellar hemisphere.

INTERPRETATIONS

A new finding in this study is that MI of brisk walking in young healthy individuals strongly involves processes lateralized in right fronto-parietal regions along with left cerebellum. These results show that brisk walking might be a non automatic locomotor activity requiring a high-level supraspinal control.

The roles of COMT val158met status and aviation expertise in flight simulator performance and cognitive ability

The polymorphic variation in the val158met position of the catechol-O-methyltransferase (COMT) gene is associated with differences in executive performance, processing speed, and attention. The purpose of this study is: (1) replicate previous COMT val158met findings on cognitive performance; (2) determine whether COMT val158met effects extend to a real-world task, aircraft navigation performance in a flight simulator; and (3) determine if aviation expertise moderates any effect of COMT val158met status on flight simulator performance. One hundred seventy two pilots aged 41-69 years, who varied in level of aviation training and experience, completed flight simulator, cognitive, and genetic assessments. Results indicate that although no COMT effect was found for an overall measure of flight performance, a positive effect of the met allele was detected for two aspects of cognitive ability: executive functioning and working memory performance. Pilots with the met/met genotype benefited more from increased levels of expertise than other participants on a traffic avoidance measure, which is a component of flight simulator performance. These preliminary results indicate that COMT val158met polymorphic variation can affect a real-world task.

Executive function, memory, and gait speed decline in well-functioning older adults

BACKGROUND

In community-dwelling older adults, global cognitive function predicts longitudinal gait speed decline. Few prospective studies have evaluated whether specific executive cognitive deficits in aging may account for gait slowing over time.

METHODS

Multiple cognitive tasks were administered at baseline in 909 participants in the Health, Aging, and Body Composition Study Cognitive Vitality Substudy (mean age 75.2 ± 2.8 years, 50.6% women, 48.4% black). Usual gait speed (m/s) over 20 minutes was assessed at baseline and over a 5-year follow-up.

RESULTS

Poorer performance in each cognitive task was cross-sectionally associated with slower gait independent of demographic and health characteristics. In longitudinal analyses, each 1 SD poorer performance in global function, verbal memory, and executive function was associated with 0.003-0.004 m/s greater gait speed decline per year (p =.03-.05) after adjustment for baseline gait speed, demographic, and health characteristics.

CONCLUSIONS

In this well-functioning cohort, several cognitive tasks were associated with gait speed cross-sectionally and predicted longitudinal gait speed decline. These data are consistent with a shared pathology underlying cognitive and motor declines but do not suggest that specific executive cognitive deficits account for slowing of usual gait in aging.

When does walking alter thinking? Age and task associated findings

Age-associated changes in gait are exacerbated when another task is performed simultaneously. We quantified the converse, i.e., the effects of walking on cognitive abilities, and determined the role of aging and executive function (EF) in any observed changes. 276 healthy older adults and 52 healthy young adults performed three cognitive tasks, i.e., serial 7 and 3 subtractions and phoneme-monitoring, while sitting and again while walking. Among the elderly, walking decreased performance on serial 3 and 7 subtractions and the number of phonemes counted (p<0.0001), but enhanced content recall. In contrast, for the young adults, walking did not alter serial 3 subtractions, phoneme-monitoring or content recall, while serial 7 subtraction performance decreased during walking (p=0.047). Measures of EF explained the age-associated changes in performance of the cognitive task during walking. Findings in both young and old subjects underscore the idea that gait is attention-demanding and is not a purely motor task. Even young, healthy adults demonstrate decreased cognitive performance while walking, when the cognitive task is sufficiently difficult. Age-associated declines in EF apparently contribute to the difference in dual tasking abilities during walking between young and older adults.