Functional analysis of genes implicated in Down syndrome: 2. Laterality and corpus callosum size in mice transpolygenic for Down syndrome chromosomal region -1 (DCR-1)

Delays in Motor Development in Children with Down Syndrome

Background

Children with Down syndrome (DS) present with delays in motor development. The reduced size of the cerebrum, brain maturation disorders, and pathophysiological processes lead to motor development delay. The aim of this study was to examine the gross motor function and estimate what motor abilities are significantly delayed in children with Down syndrome even if they attend physical therapy sessions. Another purpose of the study was to assess the functional balance.

Material/Methods

The study group consisted of 79 children with DS (42 boys, 37 girls), average age 6 years and 3 months ±4 years and 6 months. Participants were divided into 3 groups according to (i) age: <3 years old, 3–6 years old, and >6 years old; and (ii) motor impairment scale: mild (SNR 1), moderate (SNR 2), and severe (SNR 3). Children were assessed using the Gross Motor Function Measure-88 (GMFM-88) and Pediatric Balance Scale (PBS).

Results

None of the assessed children developed all the functions included in GMFM-88. The standing position was achieved at the specified age by 10% of children in the first age group (<3 years old) and 95% of children aged 3–6 years. Similarly, the walking ability was performed by 10% of children under 3 years old and by 95% of children aged 3–6 years. The median score of PBS was 50 points (min. 34 p. – max. 56 p.). There was a statistically significant correlation between PBS scores and GMFM-88 scores, r=0.7; p<0.0001, and between balance scores and GMFM – 88 E (walking, running, jumping) (r=0.64; p<0.0001).

Conclusions

Motor development, especially standing position and walking ability, is delayed in children with Down syndrome. Balance and motor functions are correlated with each other, so both aspects of development should be consider together in physical therapy of children with Down syndrome.

Handedness and corpus callosal morphology in Williams syndrome

Williams syndrome is a neurodevelopmental genetic disorder caused by a hemizygous deletion on chromosome 7q11.23, resulting in atypical brain structure and function, including abnormal morphology of the corpus callosum. An influence of handedness on the size of the corpus callosum has been observed in studies of typical individuals, but handedness has not been taken into account in studies of callosal morphology in Williams syndrome. We hypothesized that callosal area is smaller and the size of the splenium and isthmus is reduced in individuals with Williams syndrome compared to healthy controls, and examined age, sex, and handedness effects on corpus callosal area. Structural magnetic resonance imaging scans were obtained on 25 individuals with Williams syndrome (18 right-handed, 7 left-handed) and 25 matched controls. We found that callosal thickness was significantly reduced in the splenium of Williams syndrome individuals compared to controls. We also found novel evidence that the callosal area was smaller in left-handed participants with Williams syndrome than their right-handed counterparts, with opposite findings observed in the control group. This novel finding may be associated with LIM-kinase hemizygosity, a characteristic of Williams syndrome. The findings may have significant clinical implications in future explorations of the Williams syndrome cognitive phenotype.

Reversal of handedness effects on bimanual coordination in adults with Down syndrome

BACKGROUND

Research on unimanual tasks suggested that motor asymmetries between hands may be reduced in people with Down syndrome. Our study examined handedness (as assessed by hand performance) and perceptual-motor integration effects on bimanual coordination.

METHODS

Adults with Down syndrome (13 non-right-handed, 22 right-handed), along with comparison groups of adults (16 non-right-handed, 21 right-handed) and children (15 non-right-handed, 22 right-handed) without Down syndrome, drummed with auditory, verbal and visual instructions.

RESULTS

In contrast to handedness effects in the children and adults without Down syndrome, right-handed participants with Down syndrome led more with the left hand, and had lower coordination stability than non-right-handed participants with Down syndrome.

CONCLUSIONS

The reversed handedness effect during bimanual coordination suggests a complex relationship between handedness and task requirements in adults with Down syndrome.

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.

Hand-preference training in the mouse reveals key elements of its learning and memory process and resolves the phenotypic complexity in the behaviour

Handedness in the mouse comprises 2 different behaviours. Some strains have a conditional behaviour, in that the mice learn a direction of hand preference in response to reaching for food, whereas other strains have an innate or constitutive behaviour, and prior experience has no measurable effect on their hand preference. However, hybrids from different strains have revealed both recessive and dominant forms of constitutive hand preference. We proposed that kinetic parameters of the learning process would resolve this genetic heterogeneity as well as the phenotypic complexity in the behaviour. We conducted and report here a detailed kinetic analysis of hand-preference training in the C57BL/6J strain. It revealed elements of the fundamental process of learning and long-term memory that underlies the behaviour by documenting consolidation of memory, blocking of this consolidation by an inhibitor of protein synthesis, retention of memory, and speed of learning in response to training reaches. Furthermore, speed of learning is clearly described by 2 parameters that we call "capacity" (or maximum amount of learned preference) and "ability" (or number of training reaches to achieve half the capacity). These 2 kinetic parameters can vary independently among genetically different strains that learn a preference, and we used them to demonstrate that the respective recessive and dominant forms of constitutive hand-preference may be the consequence of a true null or loss of function and a gain of function, possibly a memory regulator, in the learning process. The quantitative measures provide a sensitive and selective method to establish the fundamental learning process underlying mouse hand preference and to demonstrate empirically how genes and contextual environment shape its phenotypic complexity.

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.

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

Persons with trisomy 21 (T21) and Williams-Beuren syndrome (WBS) have different brain abnormalities which may affect manual laterality. We assessed 45 persons with T21 and 34 with WBS (mean age 13) and 81 typically developing children (TD). Manual laterality was assessed with a fifteen-item task administered two times, and Bishop's card-reaching task. We found more left-handers in the T21 group compared to the other two groups. Inconsistent laterality was higher in the two groups with genetic diseases than in the TD group. For Bishop's test, both T21 and WBS participants were less right-oriented than the TD group. They displayed different response patterns in midline crossing when reaching for the cards, but did not display more midline crossing inhibition than the TD group. Is atypical handedness linked to specific genetic syndromes and, more specifically for persons with T21, to the trisomy of some of the genes?

Mouse Models of Cognitive Disorders in Trisomy 21: A Review

Trisomy 21 (TRS21) is the most frequent genetic cause of mental retardation. Although the presence of an extra copy of HSA21 is known to be at the origin of the syndrome, we do not know which 225 HSA21 genes have an effect on cognitive processes. Mouse models of TRS21 have been developed using syntenies between HSA21 and MMU16, MMU10 and MMU17. Available mouse models carry extra fragments of MMU16 or of HSA21 that cover all of HSA21 (chimeric HSA21) or MMU16 (Ts16); some carry large parts of MMU16 (Ts65Dn, Ts1Cje, Ms1Cje), while others have reduced contiguous fragments covering the D21S17-ETS2 region or single transfected genes. This offers a nest design strategy for deciphering cognitive (learning, memory and exploration) and associated brain abnormalities involving each of these chromosomal regions. This review confirms the crucial but not exclusive contribution of the D21S17-ETS2 region encompassing 16 genes to cognitive disorders.

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.