Language and executive functioning in young adults with Down syndrome

Dysfunctions of cellular context-sensitivity in neurodevelopmental learning disabilities

Pyramidal neurons have a pivotal role in the cognitive capabilities of neocortex. Though they have been predominantly modeled as integrate-and-fire point processors, many of them have another point of input integration in their apical dendrites that is central to mechanisms endowing them with the sensitivity to context that underlies basic cognitive capabilities. Here we review evidence implicating impairments of those mechanisms in three major neurodevelopmental disabilities, fragile X, Down syndrome, and fetal alcohol spectrum disorders. Multiple dysfunctions of the mechanisms by which pyramidal cells are sensitive to context are found to be implicated in all three syndromes. Further deciphering of these cellular mechanisms would lead to the understanding of and therapies for learning disabilities beyond any that are currently available.

Sustainability of personal social networks of people with Down syndrome

Research continues to demonstrate that the characteristics of one's social network could have an impact on the development of Alzheimer's disease. Given the predisposition of people with Down syndrome to develop Alzheimer's disease, analysis of their social networks has become an emerging focus. Previous pilot research demonstrated that the personal networks of people with DS could be quantitatively analyzed, with no difference between self-report and parent-proxy report. This manuscript focuses on a 12-month follow-up period with the same original participants (24 adults with Down syndrome). Their social networks demonstrated sustainability, but not improvement, as reported by people with DS (mean network size: 8.88; mean density: 0.73; mean constraint: 0.44; mean effective size: 3.58; mean max degree: 6.04; mean degree: 4.78) and their proxies (mean network size: 7.90; mean density: 0.82; mean constraint: 53.13; mean effective size: 2.87; mean max degree: 5.19; mean degree: 4.30). Intentional and continued efforts are likely needed in order to improve the social network measures of people with Down syndrome.

Cross-Sectional Analysis of Caregiver-Reported Expressive Language Profiles and Associated Covariates in Individuals with Down Syndrome

OBJECTIVE

To describe the distribution of expressive language abilities of individuals with Down syndrome (DS) in a clinical sample and characterize demographic, environmental, and medical factors associated with varying expressive language profiles.

METHODS

Cross-sectional analysis was completed on a sample of 345 individuals with DS between the ages of 4 and 22 years who were enrolled into a longitudinal clinical database between March 2018 and August 2021. Expressive language-related items on a standardized caregiver-reported questionnaire assessing domains of functioning in neurodevelopmental disorders were used to conduct latent variable modeling and determine caregiver-reported expressive language (CREL) classes across the sample. Linear regression was used to explore associations between CREL classes and predictor variables.

RESULTS

Latent variable modeling revealed 3 distinct classes of CREL abilities representing higher, middle, and lower CREL. Individuals in the lower CREL class were more likely to be female, to use sign language or visual communication systems, have reduced pronunciation, attend private or residential school, and to be in a substantially separate classroom. Membership was not predicted by complex medical histories or co-occurring neurodevelopmental diagnoses.

CONCLUSION

Caregiver-reported expressive language abilities in a cohort of individuals with DS were variable, with most of the individuals belonging to higher or middle CREL classes, relative to one another. Additional studies are indicated to understand factors that predict higher expressive language ability and explore how to direct services to individuals who are at risk of more profound language delays.

Motor Skills and Executive Functions in Pediatric Patients with Down Syndrome: A Challenge for Tailoring Physical Activity Interventions

Down syndrome (DS) is one of the most common chromosomal disorders. In addition to this variety of dysmorphic features. DS is also associated with a wide range of diseases and related comorbidities affecting different organs and systems. These comorbidities, together with societal and environmental influences, have a negative impact on physical activity in people with DS. Low levels of physical activity and energy expenditure have been identified as crucial players in worsening the acquisition of motor skills and executive functions. Executive functions are critical for the many skills (creativity, flexibility, self-control, and discipline) impacting our quality of life and make it possible to control impulses, mentally play with ideas, and stay focused. We proposed a broad overview of the available literature regarding motor skills and executive functions in pediatric patients with DS to understand the specific challenges for tailoring physical activity interventions. Motor skill interventions are effective in improving motor competence and performance on cognitive, emotional, and physical aspects in children with DS. Interventions based on executive functions in DS subjects are effective to contrast the cognitive decline and improve the everyday use of executive functions in youth and adults. Targeted interventions are mandatory for maximizing the benefits of physical activity, minimizing potential risks, and ultimately improving the overall health outcomes and quality of life for individuals with DS.

Psychometric properties of inhibitory control measures among youth with Down syndrome

BACKGROUND

Inhibitory control measures have been commonly used when assessing individuals with Down syndrome. However, minimal attention has been devoted to evaluating the appropriateness of specific assessments for use in this population, potentially leading to erroneous conclusions. This study aimed to examine the psychometric properties of measures of inhibitory control among youth with Down syndrome. We sought to examine the feasibility, presence of floor or practice effects, test-retest reliability, convergent validity and correlations with broader developmental domains of a set of inhibitory control tasks.

METHODS

A sample of 97 youth with Down syndrome aged 6 to 17 years old participated in verbal and visuospatial tasks of inhibitory control including the Cat/dog Stroop, Neuropsychological Assessment Second Edition (NEPSY-II) Statue, National Institutes of Health (NIH) Toolbox Cognition Battery (TCB) Flanker, Leiter-3 Attention Sustained, and the Test of Attentional Performance for Children (KiTAP) Go/No-go and Distractibility subtests. Youth also completed standardised assessments of cognition and language, and caregivers completed rating scales. Psychometric properties on the tasks of inhibitory control were evaluated against a priori criteria.

RESULTS

Apart from demonstrating negligible practice effects, adequate psychometric properties were not observed for any inhibitory control measure within the current sample's age range. One task with low working memory demands (NEPSY-II Statue) generally had better psychometric properties than the other tasks assessed. Subgroups of participants with an IQ greater than 30 and age more than 8 years were shown to be more likely to be able to complete the inhibition tasks.

CONCLUSIONS

Findings suggest better feasibility for analogue tasks rather than computerised assessments of inhibitory control. Given the weak psychometrics of several common measures, future studies are required to evaluate other inhibitory control measures, specifically those with reduced working memory demands for youth with Down syndrome. Recommendations for use of the inhibitory control tasks among youth with Down syndrome are provided.

Cognitive-motor interference during standing stance across different postural and cognitive tasks in individuals with Down syndrome

BACKGROUND

Individuals with Down syndrome (DS) presented both cognitive and motor impairments that could influence each other. Therefore, exploring cognitive-motor interference during standing stance is relevant in this population.

AIMS

This study explored the dual task (DT) effects on postural balance during diverse cognitive tasks and sensory manipulations in individuals with DS, compared to those with typical development (TD).

METHODS AND PROCEDURES

Fifteen adolescents with DS (age = 14.26 ± 1.27 years; height = 1.50 ± 0.02; weight = 46.46 ± 4.03 kg; BMI =20.54 ± 1.51 kg/m²) and thirteen with TD (age = 14.07 ± 1.11 years; height = 1.50 ± 0.05; weight = 44.92 ± 4.15 kg; BMI =19.77 ± 0.94 kg/m²) participated in this study. Postural and cognitive performances for the selective span task (SST) and the verbal fluency (VF) were recorded during single task (ST) and DT conditions. Postural conditions were: firm eyes open (firm-EO), firm eyes closed (firm-EC) and foam-EO. Motor and cognitive DT costs (DTC) were calculated and analyzed across these different cognitive and postural conditions.

OUTCOMES AND RESULTS

In the DS group, postural performance was significantly (p < 0.001) altered during all DT conditions, compared to the ST situation. Moreover, the motor DTC was significantly (p < 0.001) higher while performing the VF task than the SST. However, in the control group, postural performance was significantly (p < 0.001) impaired only while performing the VF test in the DT-Firm EO condition. For both groups, cognitive performances were significantly (p < 0.05) altered in all DT conditions compared to the ST one.

CONCLUSION

Adolescents with DS are more prone to DT effects on postural balance than those with TD.

Evaluating Processing Speed and Reaction Time Outcome Measures in Children and Adolescents with Down Syndrome

Reliable and valid cognitive outcome measures, including examiner-administered and computer-facilitated assessments of processing speed and reaction time, are necessary for future clinical trials that include individuals with Down syndrome (DS). The current study evaluated the score distributions and psychometric properties of four examiner-administered and three computerized processing speed and reaction time measures. Participants included 97 individuals with DS, aged 6 to 17 (M = 12.6, SD = 3.3). Two examiner-administered measures (Differential Ability Scales-II Rapid Naming and Cat/dog Stroop Congruent) met most predetermined psychometric criteria. Other assessments demonstrated good test-retest reliability and had negligible practice effects but lacked adequate feasibility. Recommendations for using processing speed and reaction time assessments in research and suggestions for modifications of measures are discussed.

Cognitive flexibility assessment in youth with Down syndrome: Reliability, practice effects, and validity

BACKGROUND

Cognitive flexibility refers to the ability to switch between different mental sets, tasks, or strategies and is challenging for some individuals with Down syndrome (DS). The lack of reliable and valid cognitive flexibility measures for individuals with DS is a major barrier to clinical trials and intervention studies designed to address cognitive challenges specific to DS. To avoid measurement limitations that could confound interpretations of performance in clinical trials in children with DS, it is critical to use phenotype-sensitive and psychometrically sound measures of cognitive flexibility.

AIM

This study aimed to evaluate the psychometric properties of three measures of cognitive flexibility including Rule-Shift, Weigl Sorting, and KiTAP Flexibility in a sample of 97 youth with DS aged 6-17 years old.

METHOD

Data were collected at two time points with a two-week interval. Parents also completed adaptive behavior and cognitive flexibility questionnaires. Child cognitive and language abilities were also assessed.

RESULTS

The Weigl Sorting met the most psychometric criteria, with adequate feasibility (≥ 80 %) and significant correlations with most of the broader developmental domains; however, the levels of test-retest reliability, practice effects, and convergent validity did not meet a priori criteria. Rule-Shift and KiTAP Flexibility measures did not have acceptable feasibility; although sensitivity and specificity analyses revealed that Rule-Shift may be appropriate for a subgroup of the participants.

CONCLUSION

No evaluated measures met all psychometric study criteria and, therefore, additional evaluation of cognitive flexibility measures is needed for use among individuals with DS.

Confirmatory factor analysis of the BRIEF2 in a sample of youth with Down syndrome

BACKGROUND

The factor structure of the Behavior Rating Inventory of Executive Function, second edition (BRIEF2) has been widely examined in both typically developing children and specific clinical samples. Despite the frequent use of the BRIEF2 for measuring executive functioning in individuals with Down syndrome, no study has investigated the factorial validity or dimensionality of the BRIEF2 in this population. This study aimed to address this notable gap in the literature.

METHODS

Parents of 407 children and youth with Down syndrome aged 6-18 years completed the BRIEF2 as part of different studies led by six sites. Three competing models proposed by previous studies were analysed using Confirmatory Factor Analysis: the theoretical structure of the BRIEF2 where the scales were constrained to load on three factors labelled as Cognitive, Behavioral, and Emotional Regulation, a two-factor correlated model with the merged Behavioral and Emotional regulation, and a single-factor model.

RESULTS

The three-factor model provided a better fit than the one- and two-factor models, yet a large correlation was observed between Behavioural and Emotional regulation factors. The results provide meaningful explanatory value for the theoretical structure of the BRIEF2. However, the Behavioral and Emotional regulation factors might be less differentiated and the two-factor structure of the BRIEF2 may also make theoretical and empirical sense.

CONCLUSIONS

Although more studies are needed to further examine the factor structure of the BRIEF2 in youth with Down syndrome, this investigation provides preliminary support for the interpretation of the three executive function index scores provided by the BRIEF2: Cognitive, Behavioral, and Emotional Regulation.

Executive functioning and verbal fluency performance in youth with Down syndrome

BACKGROUND

Executive functioning (EF) is an area of challenge for individuals with Down syndrome (DS) associated with a variety of downstream difficulties. Verbal fluency performance is one potential downstream effect that is commonly assessed in individuals with DS due to the measure's utility as a predictor of dementia. Verbal fluency requires individuals to inhibit irrelevant responses, shift between groupings of related words, and monitor to prevent repetition, all skills related to EF.

AIMS

This study aimed to determine the association between semantic verbal fluency performance and three EF subdomains (inhibition, shifting, and working memory) in youth with DS after taking into account vocabulary and cognitive ability.

METHODS AND PROCEDURES

Neuropsychological assessments (verbal and visuospatial), and parent reports of EF, were completed at one time point by 69 youth with DS 6-17 years old and their caregivers. Expressive and receptive vocabulary skills and cognitive ability were also assessed.

OUTCOMES AND RESULTS

The results revealed that verbal fluency performance was significantly associated with neuropsychological assessments of EF and parent report of inhibition even after controlling for the effects of vocabulary and cognitive ability.

CONCLUSIONS AND IMPLICATIONS

The findings highlight the underlying importance of EF in verbal fluency tasks in youth with DS.

Cognitive outcome measures for tracking Alzheimer's disease in Down syndrome

Down syndrome (DS) is now viewed as a genetic type of Alzheimer's disease (AD), given the near-universal presence of AD pathology in middle adulthood and the elevated risk for developing clinical AD in DS. As the field of DS prepares for AD clinical intervention trials, there is a strong need to identify cognitive measures that are specific and sensitive to the transition from being cognitively stable to the prodromal (e.g., Mild Cognitive Impairment-Down syndrome) and clinical AD (e.g., Dementia) stages of the disease in DS. It is also important to determine cognitive measures that map onto biomarkers of early AD pathology during the transition from the preclinical to the prodromal stage of the disease, as this transition period is likely to be targeted and tracked in AD clinical trials. The present chapter discusses the current state of research on cognitive measures that could be used to screen/select study participants and as potential outcome measures in future AD clinical trials with adults with DS. In this chapter, we also identify key challenges that need to be overcome and questions that need to be addressed by the DS field as it prepares for AD clinical trials in the coming years.

Executive function and intellectual disability: innovations, methods and treatment

This editorial presents an introduction to and an overview of the current JIDR special issue on "Executive Function in Intellectual Disability." The articles included in this special issue provide a contemporary, in depth exploration of questions regarding the nature of EF in individuals with ID. Topics include the emergence of EF during early childhood in ID-related conditions, the influence of EF on other domains of development, and the relationship between EF and adaptation throughout the lifespan. This editorial synthesizes the findings presented in this special issue and identifies methodological challenges that researchers will continue to face in future investigations of this important area.