Behavioral phenotype of individuals with Down syndrome

Peer-related social competence of young children with Down syndrome

The peer-related social competence of children with Down syndrome was examined in an observational study. Dyadic interactions with peers of children with Down syndrome were compared with the dyadic interactions of matched groups of typically developing children and with playmates differing in both familiarity and social skills. Results suggested that both risk and protective factors influenced the peer interactions of children with Down syndrome. Recommendations are made for applying contemporary models of peer-related social competence to etiologic subgroups to better understand the mechanisms involved and to provide direction for the design of intervention programs.

Is the good-imitator-poor-talker profile syndrome-specific in Down syndrome?: evidence from standardised imitation and language measures

The emergence of the Down syndrome (DS) behavioural phenotype during early development may be of great importance for early intervention. The main goal of this study was to investigate the good-imitator-poor-talker developmental profile in DS at preschool age. Twenty children with Down syndrome (DS; mean nonverbal mental age NMA 1 y10 m) and 15 children with non-specific mental retardation (NS-MR; mean NMA 1 y11 m) participated in this study. The Preschool Imitation and Praxis Scale (PIPS) and the Dutch version of the MacArthur-Bates Communicative Development Inventories (N-CDI) were used to determine absolute and relative (contrasted to a nonverbal mental age reference) imitation and language abilities. Results revealed that there was clear evidence for a good-imitator-poor-talker profile in preschoolers with DS. However, only the advanced bodily imitation ability seems to be syndrome-specific. Clinical implications of these findings are considered.

Narrative Skill in Boys with Fragile X Syndrome with and without Autism Spectrum Disorder

We examined recalled narratives of boys with fragile X syndrome with autism spectrum disorder (FXS-ASD; N=28) and without ASD (FXS-O; N=29), and compared them to those of boys with Down syndrome (DS; N=33) and typically developing boys (TD; N=39). Narratives were scored for mentions of macrostructural Story Grammar elements (Introduction, Relationship, Initiating Events, Internal Response, Attempts/Actions, and Ending). We found that narrative recall is predicted by short-term memory and nonverbal mental age levels in almost all groups (except TD), but not by expressive syntax or caregiver education. After adjusting for these covariates, there were no differences between the three groups with intellectual disability (ID). The FXS-ASD group, however, had significantly poorer performance than the TD group on the overall Story Grammar score, and both the FXS-O and FXS-ASD groups had lower Attempts/Actions scores than the TD group. We conclude that some form of narrative impairment may be associated with FXS, that this impairment may be shared by other forms of ID, and that the presence of ASD has a significantly detrimental effect on narrative recall.

Effects of individual segmental trisomies of human chromosome 21 syntenic regions on hippocampal long-term potentiation and cognitive behaviors in mice

As the genomic basis for Down syndrome (DS), human trisomy 21 is the most common genetic cause of intellectual disability in children and young people. The genomic regions on human chromosome 21 (Hsa21) are syntenic to three regions in the mouse genome, located on mouse chromosome 10 (Mmu10), Mmu16, and Mmu17. Recently, we have developed three new mouse models using chromosome engineering carrying the genotypes of Dp(10)1Yey/+, Dp(16)1Yey/+, or Dp(17)1Yey/+, which harbor a duplication spanning the entire Hsa21 syntenic region on Mmu10, Mmu16, or Mmu17, respectively. In this study, we analyzed the hippocampal long-term potentiation (LTP) and cognitive behaviors of these models. Our results show that, while the genotype of Dp(17)1Yey/+ results in abnormal hippocampal LTP, the genotype of Dp(16)1Yey/+ leads to both abnormal hippocampal LTP and impaired learning/memory. Therefore, these mutant mice can serve as powerful tools for further understanding the mechanism underlying cognitively relevant phenotypes associated with DS, particularly the impacts of different syntenic regions on these phenotypes.

Expressive language profiles of verbally expressive adolescents and young adults with Down syndrome or fragile X syndrome

PURPOSE

In this study, the authors examined the expressive language abilities of a subset of highly verbally expressive adolescents and young adults with Down syndrome (DS) and those with fragile X syndrome (FXS) for evidence of syndrome-related differences. FXS gender differences were also examined in an exploratory fashion.

METHOD

The authors evaluated 24 adolescents and young adults with DS, 17 adolescents and young adults with FXS, and 21 children with typical development (TD), with the groups matched on nonverbal mental age. Language ability was examined using the Oral and Written Language Scales (OWLS; Carrow-Woolfolk, 1995) and Developmental Sentence Scoring (DSS; Lee, 1974) scores derived from an oral narrative language sample.

RESULTS

Study analyses revealed the following group differences: The FXS group outperformed the DS and TD groups on the OWLS measure; the TD group outperformed both other groups on some of the DSS measures; the FXS group outperformed the DS group on the DSS Sentence Point measure; and females with FXS outperformed males with FXS on several measures.

CONCLUSIONS

Results contribute to the ongoing construction of the language phenotypes of individuals with DS and individuals with FXS and support the conclusion that there are quantitative rather than qualitative differences in their expressive language profiles.

Atypical semantic knowledge and autobiographical memory disorder in a young adult with Downs syndrome

A study of lexical semantic knowledge and autobiographical memory is described in PQ, a 22-year-old male with Downs syndrome. Performance is compared with younger typically developing verbal mental age controls. PQ's lexical stores contained a normal number of items, however, he was impaired at naming both pictures and item descriptions. PQ's own descriptions of items contained a normal volume of information, but the pattern of information differed from normal as he produced less 'sensory' and more 'thematic' and 'functional' information. PQ has an autobiographical memory deficit. His ability to recall 'specific' memories was significantly impoverished. It is suggested that both PQ's naming difficulties and his autobiographical memory disorder may reflect atypical knowledge specification with absence of distinctive featural knowledge and increased conceptual overlap and looser networks pervasive across both semantic and autobiographical memory systems.

Neural stem cells reduce hippocampal tau and reelin accumulation in aged Ts65Dn Down syndrome mice

Tau accumulation, in the form of neurofibrillary tangles (NFT), is an early neuropathological characteristic of Alzheimer's disease (AD) and early onset AD frequently seen in Down syndrome (DS). We investigated the presence of tau accumulation in the brains of aging DS mice using the Ts65Dn mouse model. All aged mice appeared to have substantial clusters of extracellular granules that were positive for tau and reelin, but not for amyloid-β or APP. These clusters were found primarily in CA1 of the hippocampus. In addition, the aged trisomic DS mice had a significantly greater accumulation of extracellular tau/reelin granular deposits compared to disomic littermates. These granules were similar to those described by others who also found extracellular proteinous granules in the brains of non-DS mice engineered to model aging and/or AD. When neural stem cells (NSC) were implanted unilaterally into the hippocampus of the Ts65Dn mice, the tau/reelin-positive granules were significantly reduced in both trisomic and disomic mice. Our findings indicate that changes in tau/reelin-positive granules could be used as an index for neuropathological assessment in aging DS and AD. Furthermore, changes in granule density could be used to test the efficacy of novel treatments, such as NSC implantation. Lastly, it is speculated that the unique abilities of NSC to migrate and express growth factors might be a contributing factor to reducing tau/reelin accumulation in aging DS and AD.

Social reasoning skills in adults with Down syndrome: the role of language, executive functions and socio-emotional behaviour

BACKGROUND

Although the prevalence of mental illness and behaviour problems is lower in adults with Down syndrome (DS) than in other populations with intellectual disabilities, they do present emotional and relational problems, as well as social integration difficulties. However, studies reporting on specific competences known to be central in developing appropriate social relationships (e.g. social reasoning, emotion processing, theory of mind) remain rare in the adult DS population and the mechanisms underlying these people's emotional and relational difficulties are unclear.

METHOD

The present study investigated the ability to understand the appropriateness of others' social behaviour in 34 adults with DS, using the Social Resolution Task (SRT). Their results were compared with those of 34 typically developing (TD) children matched for gender and receptive vocabulary. The relationships among the SRT experimental task, cognitive competences (receptive and productive vocabulary, non-verbal reasoning, inhibition, selective attention) and a caregiver-rated measure of socio-emotional behaviour were examined in the DS group.

RESULTS

The DS participants' global SRT scores did not differ from those of the controls. However, analyses of the SRT subscores revealed that the DS group identified significantly fewer inappropriate situations than the control group. Nevertheless, when they correctly identified the behaviour as inappropriate, they were as well as the controls to explain the rules underlying their responses. Regression analyses showed that receptive vocabulary and selective attention and a specific dimension of the socio-emotional profile (social relating skills) constituted the best predictors of the DS adults' performance on the SRT.

CONCLUSIONS

The main findings show that the DS participants demonstrate relatively good social reasoning skills in comparison with TD children matched for verbal age. However, the two groups present distinctions in their response patterns, and the influence of cognitive variables on success on the SRT also appears different. While selective attention skills are found to be significant predictors for both groups, the influence of receptive vocabulary level is much stronger in the DS group. The implications of particular cognitive and socio-emotional factors for success on the SRT in this group are considered in more detail.

Gene network disruptions and neurogenesis defects in the adult Ts1Cje mouse model of Down syndrome

BACKGROUND

Down syndrome (DS) individuals suffer mental retardation with further cognitive decline and early onset Alzheimer's disease.

METHODOLOGY/PRINCIPAL FINDINGS

To understand how trisomy 21 causes these neurological abnormalities we investigated changes in gene expression networks combined with a systematic cell lineage analysis of adult neurogenesis using the Ts1Cje mouse model of DS. We demonstrated down regulation of a number of key genes involved in proliferation and cell cycle progression including Mcm7, Brca2, Prim1, Cenpo and Aurka in trisomic neurospheres. We found that trisomy did not affect the number of adult neural stem cells but resulted in reduced numbers of neural progenitors and neuroblasts. Analysis of differentiating adult Ts1Cje neural progenitors showed a severe reduction in numbers of neurons produced with a tendency for less elaborate neurites, whilst the numbers of astrocytes was increased.

CONCLUSIONS/SIGNIFICANCE

We have shown that trisomy affects a number of elements of adult neurogenesis likely to result in a progressive pathogenesis and consequently providing the potential for the development of therapies to slow progression of, or even ameliorate the neuronal deficits suffered by DS individuals.

A mouse model of Down syndrome trisomic for all human chromosome 21 syntenic regions

Down syndrome (DS) is caused by the presence of an extra copy of human chromosome 21 (Hsa21) and is the most common genetic cause for developmental cognitive disability. The regions on Hsa21 are syntenically conserved with three regions located on mouse chromosome 10 (Mmu10), Mmu16 and Mmu17. In this report, we describe a new mouse model for DS that carries duplications spanning the entire Hsa21 syntenic regions on all three mouse chromosomes. This mouse mutant exhibits DS-related neurological defects, including impaired cognitive behaviors, reduced hippocampal long-term potentiation and hydrocephalus. These results suggest that when all the mouse orthologs of the Hsa21 genes are triplicated, an abnormal cognitively relevant phenotype is the final outcome of the elevated expressions of these orthologs as well as all the possible functional interactions among themselves and/or with other mouse genes. Because of its desirable genotype and phenotype, this mutant may have the potential to serve as one of the reference models for further understanding the developmental cognitive disability associated with DS and may also be used for developing novel therapeutic interventions for this clinical manifestation of the disorder.

Neuropsychological components of intellectual disability: the contributions of immediate, working, and associative memory

BACKGROUND

Efficient memory functions are important to the development of cognitive and functional skills, allowing individuals to manipulate and store information. Theories of memory have suggested the presence of domain-specific (i.e. verbal and spatial) and general processing mechanisms across memory domains, including memory functions dependent on the prefrontal cortex (PFC) and the hippocampus. Comparison of individuals who have syndromes associated with striking contrasts in skills on verbal and spatial tasks [e.g. Down syndrome (DS) and Williams syndrome (WS)] allows us to test whether or not these dissociations may extend across cognitive domains, including PFC and hippocampal memory processes.

METHODS

The profile of memory function, including immediate memory (IM), working memory (WM) and associative memory (AM), was examined in a sample of adolescents and young adults with DS (n = 27) or WS (n = 28), from which closely CA- and IQ-matched samples of individuals with DS (n = 18) or WS (n = 18) were generated. Relations between memory functions and IQ and adaptive behaviour were also assessed in the larger sample.

RESULTS

Comparisons of the two matched groups indicated significant differences in verbal IM (DS < WS), spatial IM (DS > WS) and spatial and verbal AM (DS > WS), but no between-syndrome differences in WM. For individuals with DS, verbal IM was the most related to variation in IQ, and spatial AM related to adaptive behaviour. The pattern was clearly different for individuals with WS. Verbal and spatial AM were the most related to variation in IQ, and verbal WM related to adaptive behaviour.

CONCLUSIONS

These results suggest that individuals with these two syndromes have very different patterns of relative strengths and weaknesses on memory measures, which do not fully mirror verbal and spatial dissociations. Furthermore, different patterns of memory dysfunction relate to outcome in individuals with each syndrome.

[Relevance of animal models in the study of human pathologies: a mouse model of Down syndrome]

Animal models provide a simplified representation of biological systems impossible to study directly in the human being. Regarding genetic pathologies, mouse models are the most studied since they enable to reproduce in animals the mutation of the gene or genes responsible for the disease and to study the phenotypic consequences. Down syndrome is a genetic disorder arising from the presence of a third copy of the human chromosome 21 (Hsa21) and is characterized by different degrees of phenotypic alterations including morphological, cardiac, muscular, cerebral, motor and intellectual changes. This high phenotypic heterogeneity involves genetic and environmental effects, which are impossible to dissect out in human beings. Various models in mice have been developed in order to identify the genetic and neurobiological mechanisms responsible for Down syndrome. The Tc1 mouse is the most complete genetic animal model currently available to study Down syndrome, since it carries an almost complete Hsa 21. The behavioural and electrophysiological studies of this model reveal a great similarity between the animal phenotype and the Down syndrome symptomatology, consequently this model represents a powerful genetic tool with a potential to unravel the mechanisms underlying the deficiencies array characteristic of this human condition. In the long term, Tc1 mice will contribute to the development and the screening of new therapeutics, with the goal of improving all the impairments reported in Down syndrome.

Quantification of vocal tract configuration of older children with Down syndrome: a pilot study

OBJECTIVE

To quantify the vocal tract (VT) lumen of older children with Down syndrome using acoustic reflection (AR) technology.

DESIGN

Comparative study.

SETTING

Vocal tract lab with sound-proof booth.

PARTICIPANTS

Ten children (4 males and 6 females), aged 9-17 years old diagnosed with Down syndrome. Ten typically developing children (4 males and 6 females) matched for age, gender, and race.

INTERVENTION

Each participant's vocal tract measurements were obtained by using an Eccovision Acoustic Pharyngometer.

MAIN OUTCOME MEASURES

Six vocal tract dimensional parameters (oral length, oral volume, pharyngeal length, pharyngeal volume, total vocal tract length, and total vocal tract volume) from children with Down syndrome and the typically developing children were measured and compared.

RESULTS

Children with Down syndrome exhibited small oral cavities when compared to control group (F(1,18)=6.55, p=0.02). They also demonstrated a smaller vocal tract volumes (F(1,18)=2.58, p=0.13), although the results were not statistically significant at the 0.05 level. Pharyngeal length, pharyngeal volume, and vocal tract length were not significantly different between the two groups.

CONCLUSION

Children with Down syndrome had smaller oral cavities, and smaller vocal tract volumes. No significant differences were found for pharyngeal length, pharyngeal volume, and vocal tract length between these two groups.

Computer Usage by Children with Down Syndrome

Children with Down syndrome, like neurotypical children, are growing up with extensive exposure to computer technology. Computers and computer-related devices have the potential to help these children in education, career development, and independent living. Our understanding of computer usage by this population is quite limited. Most of the software, games, and Web sites that children with Down syndrome interact with are designed without consideration of their special needs, making the applications less effective or completely inaccessible. We conducted a large-scale survey that collected computer usage information from the parents of approximately six hundred children with Down syndrome. This article reports the text responses collected in the survey and is intended as a step towards understanding the difficulties children with Down syndrome experience while using computers. The relationship between the age and the specific type of difficulties, as well as related design challenges are also reported. A number of potential research directions and hypotheses are identified for future studies. Due to limitations in survey methodology, the findings need to be further validated through hypothesis-driven, empirical studies.

Molecular and cellular mechanisms elucidating neurocognitive basis of functional impairments associated with intellectual disability in Down syndrome

Down syndrome, the most common genetic cause of intellectual disability, is associated with brain disorders due to chromosome 21 gene overdosage. Molecular and cellular mechanisms involved in the neuromorphological alterations and cognitive impairments are reported herein in a global model. Recent advances in Down syndrome research have lead to the identification of altered molecular pathways involved in intellectual disability, such as Calcineurin/NFATs pathways, that are of crucial importance in understanding the molecular basis of intellectual disability pathogenesis in this syndrome. Potential treatments in mouse models of Down syndrome, including antagonists of NMDA or GABA(A) receptors, and microRNAs provide new avenues to develop treatments of intellectual disability. Nevertheless, understanding the links between molecular pathways and treatment strategies in human beings requires further research.

Expressive language in male adolescents with fragile X syndrome with and without comorbid autism

BACKGROUND

Approximately one-quarter of individuals with fragile X syndrome (FXS) meet diagnostic criteria for autism; however, it is unclear whether individuals with comorbid FXS and autism are simply more severely affected than their peers with only FXS or whether they have qualitatively different profiles of behavioural impairments. To address this issue, variation in the FXS linguistic phenotype was examined in males with FXS with and without autism. The syndrome-specificity of the expressive language impairment of both groups of those with FXS was assessed in relation to Down syndrome. The extent to which different language sampling contexts affected expressive language in each diagnostic group was also examined.

METHOD

Spontaneous language samples were collected from male adolescents with FXS without autism (n = 20), comorbid FXS and autism (n = 8), and Down syndrome (n = 16). Syntactic complexity (indexed by mean length of utterance), expressive vocabulary (indexed by lexical diversity), talkativeness, fluency and intelligibility were assessed in two contexts: conversation and narration. Groups were matched on non-verbal IQ, non-verbal mental age and chronological age to allow the assessment of relative strengths and weaknesses across language variables.

RESULTS

Males with comorbid FXS and autism were less intelligible than males with only FXS; no other differences between these two groups were found. Participants' performance differed across contexts for syntactic complexity, lexical diversity, talkativeness and fluency.

CONCLUSIONS

These findings contribute to existing research on the behavioural profiles of individuals with FXS or FXS with autism who have low cognitive abilities. Although individuals with comorbid FXS and autism may be, as a group, more impaired than those with only FXS, data from this small sample of males with comorbid FXS and autism with low IQs suggest that their relative strengths and weaknesses in spontaneous expressive language are largely comparable and not differentially affected by the context in which their talk occurs.

The mouse model of Down syndrome Ts65Dn presents visual deficits as assessed by pattern visual evoked potentials

PURPOSE

The Ts65Dn mouse is the most complete widely available animal model of Down syndrome (DS). Quantitative information was generated about visual function in the Ts65Dn mouse by investigating their visual capabilities by means of electroretinography (ERG) and patterned visual evoked potentials (pVEPs).

METHODS

pVEPs were recorded directly from specific regions of the binocular visual cortex of anesthetized mice in response to horizontal sinusoidal gratings of different spatial frequency, contrast, and luminance generated by a specialized video card and presented on a 21-in. computer display suitably linearized by gamma correction.

RESULTS

ERG assessments indicated no significant deficit in retinal physiology in Ts65Dn mice compared with euploid control mice. The Ts65Dn mice were found to exhibit deficits in luminance threshold, spatial resolution, and contrast threshold, compared with the euploid control mice. The behavioral counterparts of these parameters are luminance sensitivity, visual acuity, and the inverse of contrast sensitivity, respectively.

CONCLUSIONS

DS includes various phenotypes associated with the visual system, including deficits in visual acuity, accommodation, and contrast sensitivity. The present study provides electrophysiological evidence of visual deficits in Ts65Dn mice that are similar to those reported in persons with DS. These findings strengthen the role of the Ts65Dn mouse as a model for DS. Also, given the historical assumption of integrity of the visual system in most behavioral assessments of Ts65Dn mice, such as the hidden-platform component of the Morris water maze, the visual deficits described herein may represent a significant confounding factor in the interpretation of results from such experiments.

Social cognition in children with Down's syndrome: challenges to research and theory building

Characterising how socio-cognitive abilities develop has been crucial to understanding the wider development of typically developing children. It is equally central to understanding developmental pathways in children with intellectual disabilities such as Down's syndrome. While the process of acquisition of socio-cognitive abilities in typical development and in autism has received considerable attention, socio-cognitive development in Down's syndrome has received far less scrutiny. Initial work in the 1970s and 1980s provided important insights into the emergence of socio-cognitive abilities in the children's early years, and recently there has been a marked revival of interest in this area, with research focusing both on a broader range of abilities and on a wider age range. This annotation reviews some of these more recent findings, identifies outstanding gaps in current understanding, and stresses the importance of the development of theory in advancing research and knowledge in this field. Barriers to theory building are discussed and the potential utility of adopting a transactional approach to theory building illustrated with reference to a model of early socio-cognitive development in Down's syndrome. The need for a more extensive model of social cognition is emphasised, as is the need for larger-scale, finer-grained, longitudinal work which recognises the within-individual and within-group variability which characterises this population. The value of drawing on new technologies and of adapting innovative research paradigms from other areas of typical and atypical child psychology is also highlighted.

Effect of leucovorin (folinic acid) on the developmental quotient of children with Down's syndrome (trisomy 21) and influence of thyroid status

Background

Seven genes involved in folate metabolism are located on chromosome 21. Previous studies have shown that folate deficiency may contribute to mental retardation in Down's syndrome (DS).

Methodology

We investigated the effect of oral folate supplementation (daily dose of 1.0±0.3 mg/kg) on cognitive functions in DS children, aged from 3 to 30 months. They received 1 mg/kg leucovorin or placebo daily, for 12 months, in a single-centre, randomised, double-blind study. Folinic acid (leucovorin, LV) was preferred to folic acid as its bioavailability is higher. The developmental age (DA) of the patients was assessed on the Brunet-Lezine scale, from baseline to the end of treatment.

Results

The intent-to-treat analysis (113 patients) did not show a positive effect of leucovorin treatment. However, it identified important factors influencing treatment effect, such as age, sex, and concomitant treatments, including thyroid treatment in particular. A per protocol analysis was carried out on patients evaluated by the same examiner at the beginning and end of the treatment period. This analysis of 87 patients (43 LV-treated vs. 44 patients on placebo) revealed a positive effect of leucovorin on developmental age (DA). DA was 53.1% the normal value with leucovorin and only 44.1% with placebo (p<0.05). This positive effect of leucovorin was particularly strong in patients receiving concomitant thyroxin treatment (59.5% vs. 41.8%, p<0.05). No adverse event related to leucovorin was observed.

Conclusion

These results suggest that leucovorin improves the psychomotor development of children with Down's syndrome, at least in some subgroups of the DS population, particularly those on thyroxin treatment.

Trial Registration

ClinicalTrials.gov, NCT00294593

Bilingualism and Children With Down Syndrome

This article discusses bilingualism and the factors that influence rate of bilingual development and fluency. Subsequently, the author highlights questions often asked regarding bilingualism and children with Down syndrome, and provides case study examples of children and bilingual language development.

Language Development in Individuals with Fragile X Syndrome

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability. The syndrome is caused by a single gene mutation on the X chromosome. Although individual differences are large, most individuals with FXS display weaknesses across all language and literacy domains compared to peers of the same chronological age with typical cognitive and language development. Expressive, receptive, and pragmatic language abilities as well as literacy skills are similar to those of younger, typically developing peers at similar cognitive and language developmental levels, although there are areas in which impairments exceed developmental-level expectations. One area of special impairment is the higher occurrence of repetition in the language of individuals with FXS compared to developmentally matched peers. In this paper, we review the behavioral, language, and literacy characteristics of individuals with FXS and discuss potential clinical implications.

Language Characteristics of Individuals with Down Syndrome

On average, language and communication characteristics of individuals with Down syndrome (the most common genetic cause of intellectual disability) follow a consistent profile. Despite considerable individual variability, receptive language is typically stronger than expressive language, with particular challenges in phonology and syntax. We review the literature on language and literacy skills of individuals with Down syndrome, with emphasis on the areas of phonology, vocabulary, syntax, and pragmatics. We begin by describing the hearing, oral-motor, cognitive, social, and prelinguistic and early nonverbal communication characteristics of individuals with Down syndrome. We conclude with a discussion of clinical implications and research directions.

Impairments in motor coordination without major changes in cerebellar plasticity in the Tc1 mouse model of Down syndrome

Down syndrome (DS) is a genetic disorder arising from the presence of a third copy of human chromosome 21 (Hsa21). Recently, O'Doherty et al. [An aneuploid mouse strain carrying human chromosome 21 with Down syndrome phenotypes. Science 309 (2005) 2033–2037] generated a trans-species aneuploid mouse line (Tc1) that carries an almost complete Hsa21. The Tc1 mouse is the most complete animal model for DS currently available. Tc1 mice show many features that relate to human DS, including alterations in memory, synaptic plasticity, cerebellar neuronal number, heart development and mandible size. Because motor deficits are one of the most frequently occurring features of DS, we have undertaken a detailed analysis of motor behaviour in cerebellum-dependent learning tasks that require high motor coordination and balance. In addition, basic electrophysiological properties of cerebellar circuitry and synaptic plasticity have been investigated. Our results reveal that, compared with controls, Tc1 mice exhibit a higher spontaneous locomotor activity, a reduced ability to habituate to their environments, a different gait and major deficits on several measures of motor coordination and balance in the rota rod and static rod tests. Moreover, cerebellar long-term depression is essentially normal in Tc1 mice, with only a slight difference in time course. Our observations provide further evidence that support the validity of the Tc1 mouse as a model for DS, which will help us to provide insights into the causal factors responsible for motor deficits observed in persons with DS.

Intellectual disabilities and child psychiatry: looking to the future

We begin this article by examining the role of intellectual disabilities within child psychiatry, highlighting the relatively steady role of disabilities and the recent movement to examine behavior in specific genetic syndromes. We next propose five questions for future work. Questions relate to (1) specifying the nature of gene-brain-behavior connections; (2) delineating environmental effects and gene-environment interactions; (3) understanding behaviors, physical characteristics, health issues, and other personal characteristics by which children with intellectual disabilities influence others; (4) clarifying the roles of gender and aging in behavioral functioning; and (5) working to improve pharmacological, educational, and other interventions and supports for children and their families. Although great advances have occurred over the past 50 years, intellectual disability research lags behind other areas of child psychiatry; much remains to be discovered that might help these children.

Can Drug Treatments Enhance Learning in Subjects with Intellectual Disability?

Recent research has identified specific molecular mechanisms that might account for impaired learning in particular intellectual disability syndromes. These and other findings raise the possibility that targeted drug treatments might be developed to enhance learning in subjects with intellectual disability. This review considers strategies for developing treatments, and identifies critical issues that will need to be considered in such programmes.

Behavior of 10 patients with FG syndrome (Opitz-Kaveggia syndrome) and the p.R961W mutation in the MED12 gene

Opitz and Kaveggia [Opitz and Kaveggia (1974); Z Kinderheilk 117:1-18] reported on a family of five affected males with distinctive facial appearance, mental retardation, macrocephaly, imperforate anus and hypotonia. Risheg et al. [Risheg et al. (2007); Nat Genet 39:451-453] identified an identical mutation (p.R961W) in MED12 in six families with Opitz-Kaveggia syndrome, including a surviving affected man from the family reported in 1974. The previously defined behavior phenotype of hyperactivity, affability, and excessive talkativeness is very frequent in young boys with this mutation, along with socially oriented, attention-seeking behaviors. We present case studies of two older males with FG syndrome and the p.R961W mutation to illustrate how their behavior changes with age. We also characterize the behavior of eight additional individuals with FG syndrome and this recurrent mutation in MED12 using the Vineland Adaptive Behavior Scales 2nd edition, the Reiss Profile of Fundamental Goals and Motivation Sensitivities, and the Achenbach Child Behavior Checklist. Males with this MED12 mutation had deficits in communication skills compared to their socialization and daily living skills. In addition, they were at increased risk for maladaptive behavior, with a propensity towards aggression, anxiety, and inattention. Based on the behavior phenotype in 10 males with this recurrent MED12 mutation, we offer specific recommendations and interventional strategies. Our findings reinforce the importance of testing for the p.R961W MED12 mutation in males who are suspected of having developmental and behavioral problems with a clinical phenotype that is consistent with FG syndrome.

Molecular responses of the Ts65Dn and Ts1Cje mouse models of Down syndrome to MK-801

Down syndrome (DS), caused by trisomy of human chromosome 21 (chr21), is the most common genetic cause of intellectual disability. The Ts65Dn mouse model of DS is trisomic for orthologs of 94 chr21-encoded, confirmed protein-coding genes and displays a number of behavioral deficits. Recently, Ts65Dn mice were shown to be hypersensitive to the locomotor stimulatory effects of the high-affinity N-methyl-d-aspartate (NMDA) receptor (NMDAR) channel blocker, MK-801. This is consistent with the functions of several chr21 proteins that are predicted directly or indirectly to impact NMDAR function or NMDAR-mediated signaling. In this study, we show that a second mouse model of DS, the Ts1Cje, which is trisomic for 70 protein-coding genes, is also hypersensitive to MK-801. To investigate the molecular basis for the responses to MK-801, we have measured levels of a subset of chr21 and phosphorylated non-chr21 proteins, in the cortex and hippocampus of Ts65Dn and Ts1Cje mice and euploid controls, with and without treatment with MK-801. We show that in euploid mice, the chr21-encoded proteins, TIAM1 and DYRK1A, and phosphorylation of AKT, ERK1/2 and the transcription factor ELK are involved in the MK-801 response. However, in both Ts65Dn and Ts1Cje mice, levels of phosphorylation are constitutively elevated in naïve, unstimulated mice, and the MK-801-induced changes in TIAM1 and DYRK1A and in phosphorylation are either absent or abnormal, with both genotype and brain-region-specific patterns. These results emphasize the complexities of the pathway perturbations that arise with segmental trisomy.

Preservation of long-term memory and synaptic plasticity despite short-term impairments in the Tc1 mouse model of Down syndrome

Down syndrome (DS) is a genetic disorder arising from the presence of a third copy of the human chromosome 21 (Hsa21). Recently, O'Doherty and colleagues in an earlier study generated a new genetic mouse model of DS (Tc1) that carries an almost complete Hsa21. Since DS is the most common genetic cause of mental retardation, we have undertaken a detailed analysis of cognitive function and synaptic plasticity in Tc1 mice. Here we show that Tc1 mice have impaired spatial working memory (WM) but spared long-term spatial reference memory (RM) in the Morris watermaze. Similarly, Tc1 mice are selectively impaired in short-term memory (STM) but have intact long-term memory (LTM) in the novel object recognition task. The pattern of impaired STM and normal LTM is paralleled by a corresponding phenotype in long-term potentiation (LTP). Freely-moving Tc1 mice exhibit reduced LTP 1 h after induction but normal maintenance over days in the dentate gyrus of the hippocampal formation. Biochemical analysis revealed a reduction in membrane surface expression of the AMPAR (alpha-amino-3-hydroxy-5-methyl-4-propionic acid receptor) subunit GluR1 in the hippocampus of Tc1 mice, suggesting a potential mechanism for the impairment in early LTP. Our observations also provide further evidence that STM and LTM for hippocampus-dependent tasks are subserved by parallel processing streams.

A modified version of the Bayley Scales of Infant Development-II for cognitive matching of infants with and without Down syndrome

BACKGROUND

Many measures of infants' early cognitive development, including the BSID-II (The Bayley Scales of Infant Development), mix together test items that assess a number of different developmental domains including language, attention, motor functioning and social abilities, and some items contribute to the assessment of more than one domain. Consequently, the scales may lead to under- or over-estimates of cognitive abilities in some clinical samples and may not be the best measure to use for matching purposes.

METHOD

To address this issue we created a modified form of the BSID-II (the BSID-M) to provide a 'purer' assessment of the general cognitive capacities in infants with Down syndrome (DS) from 6 to 18 months of age. We excluded a number of items that implicated language, motor, attentional and social functioning from the original measure. This modified form was administered to 17 infants with Down syndrome when 6, 12 and 18 months old and to 41 typically developing infants at 4, 7 and 10 months old.

RESULTS

The results suggested that the modified form continued to provide a meaningful and stable measure of cognitive functioning and revealed that DS infants may score marginally higher in terms of general cognitive abilities when using this modified form than they might when using the standard BSID-II scales.

CONCLUSIONS

This modified form may be useful for researchers who need a 'purer' measure with which to match infants with DS and other infants with intellectual disabilities on cognitive functioning.

Mental retardation and associated neurological dysfunctions in Down syndrome: a consequence of dysregulation in critical chromosome 21 genes and associated molecular pathways

Down syndrome (DS), affecting 1/700 live births, is the major genetic cause of mental retardation (MR), a cognitive disorder with hard impact on public health. DS brain is characterized by a reduced cerebellar volume and number of granular cells, defective cortical lamination and reduced cortical neurons, malformed dendritic trees and spines, and abnormal synapses. These neurological alterations, also found in trisomic mouse models, result from gene-dosage effects of Human Chromosome 21 (HC21) on the expression of critical developmental genes. HC21 sequencing, mouse ortholog gene identification and DS mouse model generation lead to determine HC21 gene functions and the effects of protein-dosage alterations in neurodevelopmental and metabolic pathways in DS individuals. Trisomic brain transcriptome of DS patients and trisomic mouse models identified some molecular changes determined by gene-overdosage and associated dysregulation of some disomic gene expression in DS brains. These transcriptional variations cause developmental alterations in neural patterning and signal transduction pathways that may lead to defective neuronal circuits responsible for the pathogenesis of MR in DS. Recently, the first altered molecular pathway responsible of some DS phenotypes, including neurological and cognitive disorders has been identified. In this pathway, two critical HC21 genes (DYRK1A and DSCR1) act synergistically to control the phosphorylation levels of NFATc and NFATc-regulated gene expression. Interestingly, the NFATc mice show neurological dysfunctions similar to those seen in DS patients and trisomic mouse models. Treatment of DS mouse model Ts65Dn with GABA(A) antagonists allowed post-drug rescue of cognitive defects, indicating a hopeful direction in clinical therapies for MR in children with DS.

The role of color cues in facilitating accurate and rapid location of aided symbols by children with and without down syndrome

PURPOSE

This research examined how the color distribution of symbols within a visual aided augmentative and alternative communication array influenced the speed and accuracy with which participants with and without Down syndrome located a target picture symbol.

METHOD

Eight typically developing children below the age of 4 years, 8 typically developing children over the age of 4 years, and 10 children with Down syndrome participated. Participants were asked to find a target line drawing among an array of 12. Line drawings represented either foods (e.g., grapes, cherries), clothing (e.g., a red shirt, a yellow shirt), or activities (e.g., soccer, swimming). In one condition, symbols that shared a color were clustered together, creating a subgroup within which to search. In another condition, symbols that shared a color were distributed across the display, allowing each to appear individually. Dependent measures were accuracy and speed of finding the target symbol.

RESULTS

Clustering same-color symbols facilitated the speed of locating the target for all participants, and facilitated search accuracy in the younger preschool children and participants with Down syndrome. These effects held when targets were foods, clothing, or activities.

CONCLUSION

Clinicians should consider the internal color of visual symbols when constructing aided symbol displays, at least for children with Down syndrome. Further research is needed on a number of dimensions, however, including visual processing in other etiological categories, the role of background color, and the relation of color to other stimulus dimensions.

Language development in Down syndrome: from the prelinguistic period to the acquisition of literacy

Down syndrome (DS) is associated with abnormalities in multiple organ systems and a characteristic phenotype that includes numerous behavioral features. Language, however, is among the most impaired domains of functioning in DS and, perhaps, also the greatest barrier to independent meaningful inclusion in the community. In this article, we review what is known about the extent, nature, and correlates of the language and related problems of individuals with Down syndrome. In doing so, we focus largely on the syndrome-specific features of the language phenotype, although we also consider within-syndrome variation. The review focuses on the prelinguistic foundations of language and the major components of language (i.e., vocabulary, syntax, and pragmatics). We also consider two topics in the treatment and education of individuals with DS: prelinguistic communication intervention and the acquisition of literacy skills.

Syntactic complexity during conversation of boys with fragile X syndrome and Down syndrome

PURPOSE

This study compared the syntax of boys who have fragile X syndrome (FXS) with and without autism spectrum disorder (ASD) with that of (a) boys who have Down syndrome (DS) and (b) typically developing (TD) boys.

METHOD

Thirty-five boys with FXS only, 36 boys with FXS with ASD, 31 boys with DS, and 46 TD boys participated. Conversational language samples were evaluated for utterance length and syntactic complexity (i.e., Index of Productive Syntax; H. S. Scarborough, 1990).

RESULTS

After controlling for nonverbal mental age and maternal education levels, the 2 FXS groups did not differ in utterance length or syntactic complexity. The FXS groups and the DS group produced shorter, less complex utterances overall and less complex noun phrases, verb phrases, and sentence structures than did the TD boys. The FXS with ASD group and the DS group, but not the FXS-only group, produced less complex questions/negations than did the TD group. Compared with the DS group, both FXS groups produced longer, more complex utterances overall, but on the specific complexity measures, they scored higher only on questions/negations.

CONCLUSION

Boys with FXS and DS have distinctive language profiles. Although both groups demonstrated syntactic delays, boys with DS showed greater delays.

Effects of intensity of treadmill training on developmental outcomes and stepping in infants with Down syndrome: a randomized trial

BACKGROUND AND PURPOSE

Infants with Down syndrome (DS) are consistently late walkers. The purpose of this investigation was to test the effects of individualized, progressively more intense treadmill training on developmental outcomes in infants with DS.

SUBJECTS

Thirty infants born with DS were randomly assigned to receive lower-intensity, generalized treadmill training or higher-intensity, individualized training implemented by their parents in their homes.

METHODS

Research staff members monitored implementation of training, physical growth, and onset of motor milestones of all infants on a monthly basis.

RESULTS

Infants in the higher-intensity, individualized training group increased their stepping more dramatically over the course of training. Infants in the higher-intensity training group attained most of the motor milestones at an earlier mean age.

DISCUSSION AND CONCLUSION

Treadmill training of infants with DS is an excellent supplement to regularly scheduled physical therapy intervention for the purpose of reducing the delay in the onset of walking.

Grief and its complications in individuals with intellectual disability

Bereavement and loss have significant impact on the lives of individuals with intellectual disability (ID). Although there is a growing impetus to define the symptoms of grief that predict long-term functional impairment, little is known about maladaptive grieving among individuals with ID. We examine the literature concerning the phenomenology of traumatic grief (TG) in the general population, along with what is known about the manifestations of grief in individuals with ID. We then apply modern theories of grief and grief resolution to individuals with ID in order to highlight potential areas of vulnerability in this population and to lay the groundwork for interventions that will facilitate their adaptation to loss. We provide a theoretical framework for the proposition that individuals (including children and adults) with ID are more susceptible to TG, based on an increased risk of secondary loss, barriers to communicating about the loss, and difficulty finding meaning in the loss. We conclude that individuals with ID should be considered as potential candidates for targeted bereavement interventions. Further research is required, however, in order to develop population-appropriate measurement scales for testing these hypotheses.

Mental retardation in Down syndrome: From gene dosage imbalance to molecular and cellular mechanisms

Down syndrome (DS), the most frequent genetic disorder leading to mental retardation (MR), is caused by three copies of human chromosome 21 (HC21). Trisomic and transgenic mouse models for DS allow genetic dissection of DS neurological and cognitive disorders in view to identify genes responsible for these phenotypes. The effects of the gene dosage imbalance on DS phenotypes are explained by two hypotheses: the "gene dosage effect" hypothesis claims that a DS critical region, containing a subset of dosage-sensitive genes, determines DS phenotypes, and the "amplified developmental instability" hypothesis holds that HC21 trisomy determines general alteration in developmental homeostasis. Transcriptome and expression studies showed different up- or down-expression levels of genes located on HC21 and the other disomic chromosomes. HC21 genes, characterized by their overexpression in brain regions affected in DS patients and by their contribution to neurological and cognitive defects when overexpressed in mouse models, are proposed herein as good candidates for MR. In this article, we propose a new molecular and cellular mechanism explaining MR pathogenesis in DS. In this model, gene dosage imbalance effects on transcriptional variations are described considering the nature of gene products and their functional relationships. These transcriptional variations may affect different aspects of neuronal differentiation and metabolism and finally, determine the brain neuropathologies and mental retardation in DS.

Physical activity in infants with Down syndrome receiving a treadmill intervention

Despite the recognized relevance of physical activity in the development and health of children, assessment of physical activity levels (PA-level) in infancy is limited, especially in infants with Down syndrome (DS). Increasing PA-level using a treadmill training (TMT) intervention may benefit infants with motor delays. The purpose of this study was to investigate whether a higher intensity, individualized TMT protocol (HI) would elicit immediate and short-term higher PA-level in infants with DS than a lower intensity, generalized training protocol (LG). Thirty infants with DS were randomly assigned to the LG or the HI group. Training was terminated when the infants could walk three steps independently. Activity monitors were placed on infants' trunks and legs for a 24-h period every other month during the intervention phase, and at set intervals 1-year post-independent walking onset. Data were analyzed to separate sedentary-to-light activity (Lowact) and moderate-to-vigorous activity (Highact). Overall our results demonstrate that infants receiving the HI TMT had higher levels of Highact than infants in the LG group, factoring out the activity produced by the intervention itself. Infants in the LG group spent more time in Lowact than the HI group. In addition, these results seemed to be retained during the post-intervention follow-up. Despite these exciting results, more work is needed to understand the relationship of the intensity of TMT on PA-level in infants with DS, and whether PA-level and TMT are related to motor milestone achievement and/or health benefits.

Depression in children and adolescents

Primary care physicians are often the first health care providers to have contact with depressed children and adolescents. This article discusses the epidemiology, clinical features, comorbid conditions, risk and protective factors, treatment modalities, and clinical course of early-onset depression.

Defects in embryonic neurogenesis and initial synapse formation in the forebrain of the Ts65Dn mouse model of Down syndrome

Trisomy 21, one of the most prevalent congenital birth defects, results in a constellation of phenotypes collectively termed Down syndrome (DS). Mental retardation and motor and sensory deficits are among the many debilitating symptoms of DS. Alterations in brain growth and synaptic development are thought to underlie the cognitive impairments in DS, but the role of early brain development has not been studied because of the lack of embryonic human tissue and because of breeding difficulties in mouse models of DS. We generated a breeding colony of the Ts65Dn mouse model of DS to test the hypothesis that early defects in embryonic brain development are a component of brain dysfunction in DS. We found substantial delays in prenatal growth of the Ts65Dn cerebral cortex and hippocampus because of longer cell cycle duration and reduced neurogenesis from the ventricular zone neural precursor population. In addition, the Ts65Dn neocortex remains hypocellular after birth and there is a lasting decrease in synaptic development beginning in the first postnatal week. These results demonstrate that specific abnormalities in embryonic forebrain precursor cells precede early deficits in synaptogenesis and may underlie the postnatal disabilities in Ts65Dn and DS. The early prenatal period is therefore an important new window for possible therapeutic amelioration of the cognitive symptoms in DS.