Frontal white matter integrity in adults with Down syndrome with and without dementia

The LonDownS adult cognitive assessment to study cognitive abilities and decline in Down syndrome

Background: Down syndrome (DS), the most common genetic cause of intellectual disability, is associated with an ultra-high risk of developing Alzheimer’s disease. However, there is individual variability in the onset of clinical dementia and in baseline cognitive abilities prior to decline, particularly in memory, executive functioning, and motor coordination. The LonDownS Consortium aims to determine risk and protective factors for the development of dementia and factors relating to cognitive abilities in people with DS. Here we describe our cognitive test battery and related informant measures along with reporting data from our baseline cognitive and informant assessments.

Methods: We developed a cognitive test battery to assess general abilities, memory, executive function, and motor coordination abilities in adults with DS, with informant ratings of similar domains also collected, designed to allow for data on a broad range of participants. Participants (n=305) had a range of ages and abilities, and included adults with and without a clinical diagnosis of dementia.

Results: Results suggest the battery is suitable for the majority of adults with DS, although approximately half the adults with dementia were unable to undertake any cognitive task. Many test outcomes showed a range of scores with low floor and ceiling effects. Non-verbal age-adjusted IQ scores had lower floor effects than verbal IQ scores. Before the onset of any cognitive decline, females aged 16-35 showed better verbal abilities compared to males. We also identified clusters of cognitive test scores within our battery related to visuospatial memory, motor coordination, language abilities, and processing speed / sustained attention.

Conclusions: Our further studies will use baseline and longitudinal assessments to explore factors influencing cognitive abilities and cognitive decline related to ageing and onset of dementia in adults with DS.

Structural brain alterations of Down's syndrome in early childhood evaluation by DTI and volumetric analyses

OBJECTIVES

To provide an initial assessment of white matter (WM) integrity with diffusion tensor imaging (DTI) and the accompanying volumetric changes in WM and grey matter (GM) through volumetric analyses of young children with Down's syndrome (DS).

METHODS

Ten children with DS and eight healthy control subjects were included in the study. Tract-based spatial statistics (TBSS) were used in the DTI study for whole-brain voxelwise analysis of fractional anisotropy (FA) and mean diffusivity (MD) of WM. Volumetric analyses were performed with an automated segmentation method to obtain regional measurements of cortical volumes.

RESULTS

Children with DS showed significantly reduced FA in association tracts of the fronto-temporo-occipital regions as well as the corpus callosum (CC) and anterior limb of the internal capsule (p < 0.05). Volumetric reductions included total cortical GM, cerebellar GM and WM volume, basal ganglia, thalamus, brainstem and CC in DS compared with controls (p < 0.05).

CONCLUSION

These preliminary results suggest that DTI and volumetric analyses may reflect the earliest complementary changes of the neurodevelopmental delay in children with DS and can serve as surrogate biomarkers of the specific elements of WM and GM integrity for cognitive development.

KEY POINTS

• DS is the most common genetic cause of intellectual disability. • WM and GM structural alterations represent the neurological features of DS. • DTI may identify the earliest aging process changes. • DTI-volumetric analyses can serve as surrogate biomarkers of neurodevelopment in DS.

(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.

Gait dyspraxia as a clinical marker of cognitive decline in Down syndrome: A review of theory and proposed mechanisms

Down syndrome (DS) is the most common genetic cause of intellectual disability in children. With aging, DS is associated with an increased risk for Alzheimer's disease (AD). The development of AD neuropathology in individuals with DS can result in further disturbances in cognition and behavior and may significantly exacerbate caregiver burden. Early detection may allow for appropriate preparation by caregivers. Recent literature suggests that declines in gait may serve as an early marker of AD-related cognitive disorders; however, this relationship has not been examined in individuals with DS. The theory regarding gait dyspraxia and cognitive decline in the general population is reviewed, and potential applications to the population with individuals with DS are highlighted. Challenges and benefits in the line of inquiry are discussed. In particular, it appears that gait declines in aging individuals with DS may be associated with known declines in frontoparietal gray matter, development of AD-related pathology, and white matter losses in tracts critical to motor control. These changes are also potentially related to the cognitive and functional changes often observed during the same chronological period as gait declines in adults with DS. Gait declines may be an early marker of cognitive change, related to the development of underlying AD-related pathology, in individuals with DS. Future investigations in this area may provide insight into the clinical changes associated with development of AD pathology in both the population with DS and the general population, enhancing efforts for optimal patient and caregiver support and propelling investigations regarding safety/quality of life interventions and disease-modifying interventions.

Down Syndrome Developmental Brain Transcriptome Reveals Defective Oligodendrocyte Differentiation and Myelination

Trisomy 21, or Down syndrome (DS), is the most common genetic cause of developmental delay and intellectual disability. To gain insight into the underlying molecular and cellular pathogenesis, we conducted a multi-region transcriptome analysis of DS and euploid control brains spanning from mid-fetal development to adulthood. We found genome-wide alterations in the expression of a large number of genes, many of which exhibited temporal and spatial specificity and were associated with distinct biological processes. In particular, we uncovered co-dysregulation of genes associated with oligodendrocyte differentiation and myelination that were validated via cross-species comparison to Ts65Dn trisomy mice. Furthermore, we show that hypomyelination present in Ts65Dn mice is in part due to cell-autonomous effects of trisomy on oligodendrocyte differentiation and results in slower neocortical action potential transmission. Together, these results identify defects in white matter development and function in DS, and they provide a transcriptional framework for further investigating DS neuropathogenesis.

New Perspectives for the Rescue of Cognitive Disability in Down Syndrome

Down syndrome (DS) is a relatively common genetic condition caused by the triplication of human chromosome 21. No therapies currently exist for the rescue of neurocognitive impairment in DS. This review presents exciting findings showing that it is possible to restore brain development and cognitive performance in mouse models of DS with therapies that can also apply to humans. This knowledge provides a potential breakthrough for the prevention of intellectual disability in DS.

Cognitive Impairment, Neuroimaging, and Alzheimer Neuropathology in Mouse Models of Down Syndrome

Down syndrome (DS) is the most common non-lethal genetic condition that affects approximately 1 in 700 births in the United States of America. DS is characterized by complete or segmental chromosome 21 trisomy, which leads to variable intellectual disabilities, progressive memory loss, and accelerated neurodegeneration with age. During the last three decades, people with DS have experienced a doubling of life expectancy due to progress in treatment of medical comorbidities, which has allowed this population to reach the age when they develop early onset Alzheimer's disease (AD). Individuals with DS develop cognitive and pathological hallmarks of AD in their fourth or fifth decade, and are currently lacking successful prevention or treatment options for dementia. The profound memory deficits associated with DS-related AD (DS-AD) have been associated with degeneration of several neuronal populations, but mechanisms of neurodegeneration are largely unexplored. The most successful animal model for DS is the Ts65Dn mouse, but several new models have also been developed. In the current review, we discuss recent findings and potential treatment options for the management of memory loss and AD neuropathology in DS mouse models. We also review agerelated neuropathology, and recent findings from neuroimaging studies. The validation of appropriate DS mouse models that mimic neurodegeneration and memory loss in humans with DS can be valuable in the study of novel preventative and treatment interventions, and may be helpful in pinpointing gene-gene interactions as well as specific gene segments involved in neurodegeneration.

Dissecting Alzheimer disease in Down syndrome using mouse models

Down syndrome (DS) is a common genetic condition caused by the presence of three copies of chromosome 21 (trisomy 21). This greatly increases the risk of Alzheimer disease (AD), but although virtually all people with DS have AD neuropathology by 40 years of age, not all develop dementia. To dissect the genetic contribution of trisomy 21 to DS phenotypes including those relevant to AD, a range of DS mouse models has been generated which are trisomic for chromosome segments syntenic to human chromosome 21. Here, we consider key characteristics of human AD in DS (AD-DS), and our current state of knowledge on related phenotypes in AD and DS mouse models. We go on to review important features needed in future models of AD-DS, to understand this type of dementia and so highlight pathogenic mechanisms relevant to all populations at risk of AD.

Building an adaptive brain across development: targets for neurorehabilitation must begin in infancy

Much progress has been made toward behavioral and pharmacological intervention in intellectual disability, which was once thought too difficult to treat. Down syndrome (DS) research has shown rapid advances, and clinical trials are currently underway, with more on the horizon. Here, we review the literature on the emergent profile of cognitive development in DS, emphasizing that treatment approaches must consider how some "end state" impairments, such as language deficits, may develop from early alterations in neural systems beginning in infancy. Specifically, we highlight evidence suggesting that there are pre- and early postnatal alterations in brain structure and function in DS, resulting in disturbed network function across development. We stress that these early alterations are likely amplified by Alzheimer's disease (AD) progression and poor sleep. Focusing on three network hubs (prefrontal cortex, hippocampus, and cerebellum), we discuss how these regions may relate to evolving deficits in cognitive function in individuals with DS, and to their language profile in particular.

A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome

Down syndrome, which arises in individuals carrying an extra copy of chromosome 21, is associated with a greatly increased risk of early-onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP)--an Alzheimer disease risk factor--although the possession of extra copies of other chromosome 21 genes may also play a part. Further study of the mechanisms underlying the development of Alzheimer disease in people with Down syndrome could provide insights into the mechanisms that cause dementia in the general population.

Con: are we ready to translate Alzheimer's disease-modifying therapies to people with down syndrome?

BACKGROUND

Adults with Down syndrome develop Alzheimer's disease neuropathology in an age-dependent manner. This unique feature provides an opportunity to test interventions targeted for prevention of Alzheimer's disease neuropathology and dementia in Down syndrome.

DISCUSSION

In considering clinical trial designs, however, there are several challenges that we believe will be critical to examine further. These include: accuracy in dementia, mild cognitive impairment and preclinical Alzheimer's disease diagnoses in Down syndrome; clinical trial outcome measures appropriate for individuals with Down syndrome; in vivo imaging outcome measures (and practical considerations); and contributions of medical co-morbidities to disease progression. Also, when studies are designed, the molecular target may appear to be obvious (for example, targeting beta-amyloid pathology), but chromosome 21 has over 200 additional genes that could influence both positive and negative clinical trial outcomes.

SUMMARY

Observational longitudinal studies of aging in Down syndrome will be critically important as there is a need to establish sensitive clinical outcome measures and understand the consequences of gene overexpression in relation to specific interventions.