Laterality in Persons with Intellectual Disability. I—Do Patients with Trisomy 21 and Williams–Beuren Syndrome Differ from Typically Developing Persons?

Paw preferences in mice and rats: Meta-analysis

Mice and rats are among the most common animal model species in both basic and clinical neuroscience. Despite their ubiquity as model species, many clinically relevant brain-behaviour relationships in rodents are not well understood. In particular, data on hemispheric asymmetries, an important organizational principle in the vertebrate brain, are conflicting as existing studies are often statistically underpowered due to small sample sizes. Paw preference is one of the most frequently investigated forms of hemispheric asymmetries on the behavioural level. Here, we used meta-analysis to statistically integrate findings on paw preferences in rats and mice. For both species, results indicate significant hemispheric asymmetries on the individual level. In mice, 81 % of animals showed a preference for either the left or the right paw, while 84 % of rats showed this preference. However, contrary to what has been reported in humans, population level asymmetries were not observed. These results are particularly significant as they point out that paying attention to potential individual hemispheric differences is important in both basic and clinical neuroscience.

Where is the 'subjective straight ahead' in Williams syndrome?

BACKGROUND

Individuals with Williams Syndrome (WS) are known to have particular difficulties when performing visuo-spatial tasks, which could be related to their difficulties in using a specific reference system to determine spatial relations. The aim of the present study was to assess the internal representation of the body's sagittal plane, which is an important benchmark for an egocentric frame of reference.

METHOD

The results of 18 WS individuals (mean age = 20.5 ± 9.2 years) on the subjective straight ahead (SSA) task were compared with those of two healthy control groups composed of 36 participants matched on chronological age matched on chronological age (CA) and 30 young children matched on non-verbal intellectual ability (YC).

RESULTS

Individuals with WS showed a significant left deviation on the SSA body's sagittal plane representation compared with the chronological age control group and a marginal left deviation compared with the young children control group. A comparison with the objective SA (0°) showed a significant leftward deviation in the WS group but not in the two control groups.

CONCLUSIONS

Individuals with WS showed a significant leftward deviation in the SSA task. This bias of the body's longitudinal axe representation could have a negative impact on the use of an egocentric reference system, which could be the cause for their difficulties in defining spatial relations (e.g. location and orientation) necessary for performing spatial tasks.

Does Congenital Heart Disease Affect Neurodevelopmental Outcomes in Children with Down Syndrome?

OBJECTIVE

The impact that congenital heart disease (CHD) has on the neurodevelopment of children with Down syndrome (DS) is unknown and potentially has implications for targeted early intervention. This study assessed the relationship between CHD that required surgery in the first year of life and neurodevelopmental, behavioral and emotional functioning outcomes in children with DS.

METHODS

A retrospective chart review of 1092 children (0-18 years) with DS who visited a single institution from 8/08-8/13 was performed. Children who underwent at least one of nine neurodevelopmental (cognitive, language, developmental) or academic tests were included in the analysis (N = 178). Cohort was age-divided into infants/toddlers (0-2 years), preschoolers (3-5 years), and school age/adolescent (6-18 years). Test scores of children with DS who underwent cardiac surgery in the first year of life were compared to children with DS without CHD. T test, chi-square and Mann Whitney U tests were used where appropriate.

RESULTS

Infants/toddlers with cardiac surgery had lower scores for receptive (P = .01), expressive (P = .021) and composite language (P < .001) compared to those with no CHD. Preschoolers with cardiac surgery had lower language scores and lower visual motor scores, although not statistically significant. In school age children with cardiac surgery there were no differences in IQ scores, language scores, or academic achievement scores compared to those without CHD. Also at school-age there was no difference in the incidence of ADHD, executive function or on internalizing and externalizing behavior scores.

CONCLUSION

Children with DS undergoing cardiac surgery during the first year demonstrated poorer neurodevelopmental outcomes as infants/toddler but had no difference at school age compared to children with DS without CHD. These results will guide early interventions to optimize neurodevelopmental outcomes in children with DS and will help with family counseling after CHD repair.

Capacity to improve fine motor skills in Williams syndrome

BACKGROUND

Individuals with Williams syndrome (WS) are known to have difficulties in carrying out fine motor movements; however, a detailed behavioural profile of WS in this domain is still missing. It is also unknown how great the capacity to improve these skills with focused and extensive practice is.

METHOD

We studied initial performance and learning capacity in a sequential finger tapping (FT) task in WS and in typical development. Improvement in the FT task has been shown to be sleep dependent. WS subjects participating in the current study have also participated in earlier polysomnography studies, although not directly related to learning.

RESULTS

WS participants presented with great individual variability. In addition to generally poor initial performance, learning capacity was also greatly limited in WS. We found indications that reduced sleep efficiency might contribute to this limitation.

CONCLUSIONS

Estimating motor learning capacity and the depth of sleep disorder in a larger sample of WS individuals might reveal important relationships between sleep and learning, and contribute to efficient intervention methods improving skill acquisition in WS.

Forelimb preferences in human beings and other species: multiple models for testing hypotheses on lateralization

Functional preferences in the use of right/left forelimbs are not exclusively present in humans but have been widely documented in a variety of vertebrate and invertebrate species. A matter of debate is whether non-human species exhibit a degree and consistency of functional forelimb asymmetries comparable to human handedness. The comparison is made difficult by the variability in hand use in humans and the few comparable studies conducted on other species. In spite of this, interesting continuities appear in functions such as feeding, object manipulation and communicative gestures. Studies on invertebrates show how widespread forelimb preferences are among animals, and the importance of experience for the development of forelimb asymmetries. Vertebrate species have been extensively investigated to clarify the origins of forelimb functional asymmetries: comparative evidence shows that selective pressures for different functions have likely driven the evolution of human handedness. Evidence of a complex genetic architecture of human handedness is in line with the idea of multiple evolutionary origins of this trait.

Age-related changes of adaptive and neuropsychological features in persons with Down Syndrome

Down Syndrome (DS) is characterised by premature aging and an accelerated decline of cognitive functions in the vast majority of cases. As the life expectancy of DS persons is rapidly increasing, this decline is becoming a dramatic health problem. The aim of this study was to thoroughly evaluate a group of 67 non-demented persons with DS of different ages (11 to 66 years), from a neuropsychological, neuropsychiatric and psychomotor point of view in order to evaluate in a cross-sectional study the age-related adaptive and neuropsychological features, and to possibly identify early signs predictive of cognitive decline. The main finding of this study is that both neuropsychological functions and adaptive skills are lower in adult DS persons over 40 years old, compared to younger ones. In particular, language and short memory skills, frontal lobe functions, visuo-spatial abilities and adaptive behaviour appear to be the more affected domains. A growing deficit in verbal comprehension, along with social isolation, loss of interest and greater fatigue in daily tasks, are the main features found in older, non demented DS persons evaluated in our study. It is proposed that these signs can be alarm bells for incipient dementia, and that neuro-cognitive rehabilitation and psycho-pharmacological interventions must start as soon as the fourth decade (or even earlier) in DS persons, i.e. at an age where interventions can have the greatest efficacy.

Development of motor planning for dexterity tasks in trisomy 21

We examined the macroscopic aspects of motor planning in two manual dexterity tasks, comparing children, adolescents, and young adults with trisomy 21 (T21) with typically developing controls from a developmental perspective. We analyzed the order in which objects were picked up from a table during two manual tasks of the Movement Assessment Battery for Children (M-ABC). Participants with T21 were always slower than controls. Task completion times depended on the strategy used by participants to gather up the pegs or coins. A structured strategy, in which the participants picked the items up moving methodically along each row/column, contributed to rapid task completion by younger children and participants with T21. This study highlights the ability of children with T21 to select and maintain an efficient strategy that takes account of their motor difficulties. Developmental trajectories help to explain T21 functioning in these dexterity tasks.

The effect of handedness on grip strength in older adults with intellectual disabilities

Grip strength is an important predictor of several health outcomes in the general older population. Grip strength assessment is feasible and reliable in older adults with intellectual disabilities (ID), which makes it a valuable measurement for application in this population. The purpose of this study was to investigate the effect of handedness on grip strength in the older population with ID. Handedness and grip strength were assessed in a sample of 1050 older adults (≥ 50 years) with borderline to profound ID. Results showed that 26.2% of the study sample was left-handed. In right-handed participants the dominant hand (right) was on average 8.7% stronger than the non-dominant hand (p<0.001). For lefthanded participants there was no significant difference between the dominant hand (left) and nondominant hand. However, more detailed analyses revealed that 34.5% of the participants were stronger with their non-dominant hand, (on average 16.6% stronger for right-handed and 16.3% stronger for left-handed participants). Because of the large strength ratios, distributed in favor of both the dominant as the non-dominant hand, it is recommended to assess both hands to get a valid result of grip strength in older adults with ID.

Preferência podal em lactentes com síndrome de Down: fatores extrínsecos e intrínsecos

Durante o processo de aquisição do chute em lactentes, a preferência podal pode ser influenciada de forma diferente pelos fatores extrínsecos e intrínsecos. O objetivo foi comparar a preferência podal e verificar a influência do peso adicional e do Reflexo Tônico Cervical Assimétrico (RTCA) na preferência podal entre lactentes com síndrome de Down e típicos. Participaram do estudo cinco lactentes com síndrome de Down e cinco típicos aos três e quatro meses de idade. O experimento foi subdividido em quatro condições experimentais: Treinamento, Linha de Base, Peso e Pós-Peso. Os lactentes com síndrome de Down apresentaram preferência à esquerda ou indefinida e os típicos, preferência à direita. O RTCA influenciou na preferência podal em ambos os grupos, indicando que o lado de rotação da cabeça orientou o chute do mesmo lado. Nos lactentes com síndrome de Down a correlação entre RTCA e chutes foi positiva, sendo forte aos três meses e moderada aos quatro meses. Para os lactentes típicos foi observada correlação positiva fraca aos três meses, e aos quatro meses a correlação não foi estatisticamente significativa. Lactentes com síndrome de Down apresentam preferência podal contrária aos lactentes típicos. O RTCA exerce influência na preferência podal por um período mais longo em lactentes com síndrome de Down em comparação aos lactentes típicos.

Specific grasp characteristics of children with trisomy 21

Children with trisomy 21 display atypical manual skills that change to some extent during development. We examined grasp characteristics and their development in 35 children with trisomy 21, aged 4-18 years, who performed simple manual tasks (two manual tasks of the Movement Assessment Battery for Children, and grasping of five wooden blocks whose size was determined by their hand size). The age-matched comparison group included 35 typically developing children. Children with trisomy 21 were found to use fewer fingers than children in the comparison group in each task. They also used specific grasps and tended to extend fingers that were not involved in the grip. While some specific grasp characteristics of children with trisomy 21 decreased with age, other did not, and remained present throughout development. The perceptual-motor development of children with trisomy 21 should be analyzed in terms of atypical development rather than developmental delay.

Behavioural indexes of callosal functioning in Williams syndrome

Williams syndrome (WS) is a neurogenetic disorder that stems from a microdeletion on chromosome 7. Recent anatomical studies have found evidence for corpus callosum abnormalities in WS. However, to date, the impact of these structural differences on callosal functionality remains unclear. The aim of the present study was to investigate interhemispheric communication and hemispheric asymmetry in individuals with WS relative to mental age-matched controls. This was assessed using bilateral and unilateral presentations of visual stimuli in a picture-naming task. Results found both groups to exhibit a bilateral field advantage and a left visual advantage on unilateral presentations. However, while a significant performance increase with age was found for controls, no such correlation was found for individuals with WS. Taken together, these findings suggest that despite some evidence for an atypical developmental pathway in WS, both interhemispheric communication and hemispheric asymmetry are functionally intact in this population.

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.

Research Review: Williams syndrome: a critical review of the cognitive, behavioral, and neuroanatomical phenotype

This review critically examines the research findings which characterize the cognitive, behavioral, and neuroanatomical features of Williams syndrome (WS). This article analyzes 178 published studies in the WS literature covering the following areas: 1) General intelligence, 2) Language skills, 3) Visuospatial and face processing skills, 4) Behavior patterns and hypersociability, 5) Musical abilities, and 6) Brain structure and function. We identify methodological issues relating to small sample size, use and type of control groups, and multiple measures of task performance. Previously described 'peaks' within the cognitive profile are closely examined to assess their veracity. This review highlights the need for methodologically sound studies that utilize multiple comparison groups, developmental trajectories, and longitudinal analyses to examine the WS phenotype, as well as those that link brain structure and function to the cognitive and behavioral phenotype of WS individuals.

Hand preference and hand performance: cross-sectional developmental trends and family resemblance in degree of laterality

The first aim of the study was to compare developmental trends in the degree of laterality (independent of direction) observed in two handedness tasks. The second aim was to assess family resemblance in the degree of laterality using the same two tasks. The sample was comprised of 186 left-handers and 302 right-handers aged from 6 to 66. Some of the sample were members of the same families. Bishop's card-reaching task was used to assess hand preference, and Annett's peg-moving task to assess manual performance. For the card-reaching task, children aged 7 to 10/11 recorded more midline crossings than the other age groups (both younger and older). No general age-related trend was observed for the Annett pegboard. For the card-reaching task, family resemblance was very low and not significant. The degree of laterality, assessed with the peg-moving task, showed a small but significant resemblance in father-offspring pairs (sons and daughters). Putative involvement of a maternally suppressed gene on chromosome 2p12 and of the androgen receptor was discussed.

Weak hand preference in children with down syndrome is associated with language deficits

This study explores associations between language ability and hand preference in children with Down syndrome. Compared to typically developing children of the same age, children with Down syndrome showed weaker hand preference, were less consistent in the hand they used and also less willing to reach to extreme positions in contralateral space. Within the group of children with Down syndrome, those who showed a stronger or more consistent hand preference had better language and memory skills. This association could not be explained by differences in non-verbal cognitive ability or hearing loss. These findings are discussed within the theory of neurolinguistic development proposed by Locke [Locke (1997). Brain & Language, 58, 265-326].

Lateralisation of auditory processing in Down syndrome: a study of T-complex peaks Ta and Tb

It has long been argued that abnormal cerebral lateralisation might underlie the language problems that characterise Down syndrome, but to date only behavioural evidence has been provided. We used the auditory event-related potentials Ta and Tb of the T-complex to investigate lateralised processing of speech (vowels) and non-speech (simple and complex tones) sounds in children with Down syndrome and age-matched typically developing children. We also explored associations with speech and language abilities. Although changes in the Ta and Tb in response to increases in stimulus complexity and ‘speechness’ were similar across group, the Tb peak was delayed in children with Down syndrome across conditions. In addition, marked differences in the patterns of lateralisation of Ta latency and Tb amplitude were observed in children with Down syndrome, in response to both speech and non-speech sounds. No associations were found between Ta and Tb characteristics and speech and language abilities in children with DS.

Trisomy 21: From Chromosomes to Mental Retardation

The first descriptions of the trisomy 21 phenotype were by Jean-Etienne-Dominique Esquirol (1838), Edouard Séguin (1846) and later by John L. H. Down in 1862. It took more than a century to discover the extra-chromosomal origin of the syndrome commonly called "Down's syndrome" and which, we suggest, should be referred to as "Trisomy 21". In this review we are presenting the landmarks, from the pioneering description of the syndrome in 1838 to Jérôme Lejeune's discovery of the first genetic substrate for mental retardation. The sequencing of HSA21 was a new starting point that generated transcriptome studies, and we have noted that studies of gene over-expression have provided the impetus for discovering the HSA21 genes associated with trisomy 21 cognitive impairment.

Pre-weaning sensorial and motor development in mice transpolygenic for the critical region of trisomy 21

Trisomy 21 occurs every 1/800 births and is the most frequent genetic cause of mental retardation. Children with trisomy 21 show delayed sensorial and motor development as well as cognitive disorders. We selected a mouse model of trisomy 21 (TRS21): transgenic mice carrying extra copies of a HSA21 region corresponding to the D21S17-ETS2 region (previously referred to as "Down syndrome critical region 1"). Sensorial and motor development was measured in these partially transgenic mice, from birth to weaning. The four HSA21 regions contributed unequally to sensorial and motor development delay. The more centromeric region (230E8) modified 4 of the development indicators plus the size of the effect, indicated by partial eta(2)(eta(p)(2), reached a median value of 14.5%. The neighboring 141G6 region contributed to 5 developmental differences (eta(p)(2) median value 14%). The most telomeric region (285E6) only modified one development indicator. An extra copy of an HSA21 fragment (referred to here as the 152F7 region) induced modifications to 14 of the 18 indicators measured with a eta(2) median value reaching 20%. The results indicate a noticeable contribution of the 152F7 region to sensorial and motor development. The contribution of this region to cognitive functioning and its neurobiological basis has been already reported. This set of result suggests the location in the D21S17-ETS2 region of several genes playing crucial role in cognitive and developmental impairment observed in TRS21.

Laterality in persons with intellectual disability II. Hand, foot, ear, and eye laterality in persons with Trisomy 21 and Williams-Beuren syndrome

Laterality (hand, foot, ear, and eye) was assessed in participants with Trisomy 21 (62) and Williams-Beuren syndrome (WBS) (39). Handedness was also assessed in a card reaching task. The comparison group included 184 typically developing persons. Two independent age sub-groups were formed: 7 to 10 years old and 11 to 34 years old. We confirmed previous data: individuals with T21 were more frequently left- or mixed-handed than typically developing persons; individuals with WBS had intermediate scores. The two groups with genetic disorders had less right foot preference. Manual and foot inconsistencies characterized both groups with genetic disorders. Cross hand-foot preference was lower in the typically developing group. Differences in IQ levels did not correlate with differences in laterality scores. Overall laterality profiles were not the same in the two groups with genetic disorders: the greatest differences were observed between typically developing persons and persons with Trisomy 21.

Lateral preferences in children with intellectual deficiency of idiopathic origin

The goal of this study was to evaluate lateral preferences in a population of children with intellectual deficiency of idiopathic origin, compared with those of typically developing (TD) children. Two groups of children with mild or moderate intellectual deficiency were observed. Handedness (using a 10-item test and Bishop's card-reaching task), eyedness and footedness were studied. The younger group consisted of sixteen 10- to 11-year olds; the older group comprised fourteen 12- to 14-year olds. A control group of fifteen TD children was matched for age with the younger group of intellectually deficient (ID) children. The results show that the occurrence of left-handedness is not higher in children with ID of unknown origin than in age-matched TD children. However, we observed a marginally reduced tendency toward right-handedness in ID than in TD children: more mixed-handers among ID than TD children; test-retest consistency of hand preference significantly lower in the 10- to 11-year-old ID children than in the age-matched TD children; greater tendency of ID children to use their nonpreferred left hand when the card was presented to the left, as compared with TD children. Left-eyedness and crossed hand-eye preference were also more frequent in ID than in age-matched TD children. No age-related difference in laterality was found in ID children. These results partially support other studies indicating that less rightward asymmetry is associated with intellectual deficiency in children.