Low elementary movement speed is associated with poor motor skill in Turner's syndrome

White matter microstructure and functional connectivity in the brains of infants with Turner syndrome

Turner syndrome, caused by complete or partial loss of an X-chromosome, is often accompanied by specific cognitive challenges. Magnetic resonance imaging studies of adults and children with Turner syndrome suggest these deficits reflect differences in anatomical and functional connectivity. However, no imaging studies have explored connectivity in infants with Turner syndrome. Consequently, it is unclear when in development connectivity differences emerge. To address this gap, we compared functional connectivity and white matter microstructure of 1-year-old infants with Turner syndrome to typically developing 1-year-old boys and girls. We examined functional connectivity between the right precentral gyrus and five regions that show reduced volume in 1-year old infants with Turner syndrome compared to controls and found no differences. However, exploratory analyses suggested infants with Turner syndrome have altered connectivity between right supramarginal gyrus and left insula and right putamen. To assess anatomical connectivity, we examined diffusivity indices along the superior longitudinal fasciculus and found no differences. However, an exploratory analysis of 46 additional white matter tracts revealed significant group differences in nine tracts. Results suggest that the first year of life is a window in which interventions might prevent connectivity differences observed at later ages, and by extension, some of the cognitive challenges associated with Turner syndrome.

What's missing in autism spectrum disorder motor assessments?

BACKGROUND

Motor delays and impairments in autism spectrum disorders (ASD) are extremely common and often herald the emergence of pervasive atypical development. Clinical accounts of ASD and standardized measures of motor function have identified deficits in multiple motor domains. However, literature describing frequently used standardized motor assessments in children with ASD, their test properties, and their limitations are sparse.

METHODS

We systematically reviewed the literature to identify the most frequently used standardized motor assessments used to evaluate children with ASD from infancy to early childhood. All assessments included were required to possess reference norms, evaluate more than one motor domain, and have undergone some degree of validation.

RESULTS

We identified six frequently used standardized measures of motor function per our inclusion and exclusion criteria. We investigated and described in detail the psychometric properties of these assessments, their utility for use with children with ASD, and their individual and overall strengths and limitations. The global strengths of these assessments are the ability to identify early development delays and differences in fine and gross motor function in children with ASD. Global limitations of these studies are lack of validation in individuals with ASD and scoring systems that often miss specific and subtle abnormalities.

CONCLUSIONS

Standardized assessments of motor function have provided valuable information on motor impairments in ASD. However, significant limitations remain in the use of these measures in children with ASD. Moving forward, it is imperative that standardized measures of motor function receive greater validation testing in children with ASD to assess their potential application given the clinical heterogeneity of this condition. In addition, utilizing quantitative measures of motor function should allow for evaluation and comparison of individuals with ASD across the lifespan with varying cognitive and behavioral abilities.

Motor sequence learning in children with spina bifida

Cognitive and motor problems are common in children with spina bifida (SB), particularly in those children with cerebral malformations (SBM). Little is known about how these conditions affect motor learning. This study examines motor sequence learning in children with SB, SBM, and healthy controls. Assessment consisted of neuropsychological tests, a simple drawing task, and a spatial motor sequence learning task. Implicit motor learning was unaffected in children with SB(M), and their sequence learning ability was also similar to that of controls. However, both groups (SB and SBM) showed impaired motor performance. The role of cerebellar malformation with SB(M) is discussed.

Abnormal motor cortex excitability is associated with reduced cortical thickness in X monosomy

Turner syndrome (TS) is a noninherited genetic disorder caused by the absence of one or part of one X chromosome. It is characterized by physical and cognitive phenotypes that include motor deficits that may be related to neuroanatomical abnormalities of sensorimotor pathways. Here, we used transcranial magnetic stimulation (TMS) and cortical thickness analysis to assess motor cortex excitability and cortical morphology in 17 individuals with TS (45, X) and 17 healthy controls. Exploratory analysis was performed to detect the effect of parental origin of the X chromosome (X(mat), X(pat)) on both measures. Results showed that long-interval intracortical inhibition was reduced and motor threshold (MT) was increased in TS relative to controls. Areas of reduced thickness were observed in the precentral gyrus of individuals with TS that correlated with MT. A significant difference between X(mat) (n = 11) and X(pat) (n = 6) individuals was found on the measure of long-interval intracortical inhibition. These findings demonstrate the presence of converging anatomical and neurophysiological abnormalities of the motor system in X monosomy.

Motor response programming and movement time in children with heavy prenatal alcohol exposure

The present experiment assessed motor response programming and movement time in children with histories of heavy prenatal alcohol exposure (PEA). Alcohol-exposed children between the ages of 7 and 17 years were classified into two groups: Fetal Alcohol Syndrome (FAS: n=9) and children with PEA (PEA: n=19) but who did not have the defining characteristics of FAS. The FAS and PEA children were compared with non-alcohol-exposed children (NC: n=23) when completing two tasks: a simple reaction time task (RT alone condition) and a reaction plus movement task (RT+Move condition). The movement involved responding to an imperative stimulus signal and depressing three target buttons in a set sequence. Participants completed 24 trials each for the RT alone and RT+Move response conditions. Results indicated no significant differences in performance among FAS, PEA, and NC groups during the RT alone condition. However, during the RT+Move condition, the FAS group produced significantly longer and more variable RTs than the PEA and NC groups, which produced comparable RTs. The FAS group also produced significantly slower movement times when moving to all three targets, whereas movement time variability did not significantly differ as a function of group. The observed results indicate children with FAS experience deficits in response programming and movement time production.

Cerebral laterality in Turner syndrome: a critical review of the literature

Turner syndrome (TS) is a genetic disorder in females characterized by the complete or partial absence of one X chromosome. Its most consistent physical features include short stature and ovarian dysgenesis. TS individuals demonstrate a characteristic neurocognitive profile involving weaknesses in visuospatial processing. The hypothesis of defective right hemisphere specialization has been offered to explain the visuospatial deficits in TS. In contrast, an alternative explanation proposes a more uniform dysfunction of the left and right hemispheres, based on findings of symmetrical abnormalities. This article presents an overview of the two hypotheses, along with relevant findings on hemispheric specialization with respect to TS. The impact of the genetic and hormonal mechanisms on the neurocognitive profile of TS is also discussed and directions for further empirical research are identified.

Optimizing assisted communication devices for Children with motor impairments using a model of information rate and channel capacity

For children who depend on devices to communicate, the rate of communication is a primary determinant of success. For children with motor impairments, the rate of communication may be limited by inability to contact buttons or cells rapidly or accurately. It is, therefore, essential to know how to adjust the device interface in order to maximize each child's rate of communication. The optimal rate of communication is determined by the channel capacity, which is the maximum value of the information rate for all possible keyboard button or cell layouts for the communication device. We construct a mathematical model for the information rate based on the relationship between movement time and the number of buttons per screen, the size of the buttons, and the length of a sequence of buttons that must be pressed to communicate each word in the vocabulary. We measure the parameters of the model using a custom-programmed touchscreen interface in 10 children with disorders of arm movement due to cerebral palsy who use a DynaVox communication device. We measure the same parameters in 20 healthy control subjects. We show that the model approximates the measured information rate and that the information rate is lower in children with motor impairments compared with control subjects. The theory predicts that for each child there is a combination of button size and number that maximizes the predicted information rate and thereby achieves communication at the optimal channel capacity. Programming communication devices with each child's predicted optimal parameters improved the communication rate in five of the ten children, compared with programming by professionals. Therefore, measurement of information rate may provide an assessment of the effect of motor disorders on success in assisted communication. Optimization of the information rate may be useful for programming assisted communication devices.

Selective alterations of white matter associated with visuospatial and sensorimotor dysfunction in turner syndrome

Turner syndrome (TS) is a neurogenetic disorder characterized by impaired spatial, numerical, and motor functioning but relatively spared verbal ability. Results from previous neuroimaging studies suggest that gray matter alterations in parietal and frontal regions may contribute to atypical visuospatial and executive functioning in TS. Recent findings in TS also indicate variations in the shape of parietal gyri and white matter microstructural anomalies of the temporal lobe. Diffusion tensor imaging and structural imaging methods were used to determine whether 10 females with TS and 10 age- and gender-matched control subjects exhibited differences in fractional anisotropy, white matter density, and local brain shape. Relative to controls, females with TS had lower fractional anisotropy (FA) values in the deep white matter of the left parietal-occipital region extending anteriorly along the superior longitudinal fasciculus into the deep white matter of the frontal lobe. In addition, decreased FA values were located bilaterally in the internal capsule extending into the globus pallidus and in the right prefrontal region. Voxel-based morphometry (VBM) analysis showed corresponding white matter density differences in the internal capsules and left centrum semiovale. Tensor-based morphometry analysis indicated that the FA and VBM results were not attributable to differences in the local shape of brain structures. Compared with controls, females with TS had increases in FA values and white matter density in language-related areas of the inferior parietal and temporal lobes. These complementary analyses provide evidence for alterations in white matter pathways that subserve affected and preserved cognitive functions in TS.

Psychosocial Functioning after Discontinuation of Long-Term Growth Hormone Treatment in Girls with Turner Syndrome

It is common practice in the case of Turner syndrome (TS) to treat short stature with GH treatment and to induce puberty with estrogens at an age as close to normal puberty as possible. This approach in most cases leads to a height in the normal range in childhood, adolescence, and adulthood in TS. Little data is available, however, on its effect on psychosocial functioning. In the present study, we evaluated psychosocial functioning in a group of 50 women with TS, after reaching final height in two multicenter GH trials. Thirty-six girls participated in a randomized dose-response study from mean (SEM) age 6.8 (0.4) years, and 14 girls participated in a frequency-response study from age 13.2 (0.4) years. After discontinuation of long-term GH treatment, these 50 girls were evaluated for psychosocial functioning at a mean age of 18.8 (0.3) years. GH was given in a dosage of 4 IU/m2/day (approximately 0.045 mg/kg/day), 6 IU/m2/day, or 8 IU/m2/day. After a mean GH treatment duration of 7.1 (0.4) years, mean final height (ref. normal girls) was FH1.2 (0.2) SD score. Behavioral problem scores (Achenbach) of the TS women were comparable to normal Dutch peers. Although self-perception (Harter total scale: p < 0.01), and bodily attitude (Baardman: p < 0.05) was significantly less positive than for their normal Dutch peers, we found no evidence of depression. TS women rated their family functioning higher than their Dutch peers (p < 0.0001), and had a slightly different coping pattern. These results show that even after reaching a height in most cases within the normal range and puberty induction at a pubertal age, some women with TS still experience psychosocial problems. It is likely, however, that GH and estrogen treatment improved psychosocial functioning. Long-term follow-up of these GH-treated patients will allow an evaluation of their life achievements.

Reaching movements in childhood dystonia contain signal-dependent noise

When reaching, children with dystonia exhibit movements that are slower and more variable than normal children. We hypothesize that in dystonia there is an increase in signal-dependent noise so that there is increased variability with increasing speed. This hypothesis predicts that slower movement in children with dystonia is at least partly due to a compensatory strategy to reduce variability by decreasing speed. To test this hypothesis, we measured the speed of arm movement while children attempted to contact buttons of different sizes. We tested 23 control children and 15 children between the ages of 4 and 16 years with dystonia owing to either cerebral palsy, idiopathic dystonia not due to the DYT1 (torsin A) mutation, or other identified causes. A consistent inverse relationship between movement time and button size was seen for both the control children and the children with dystonia. The variance of movement speed increased with the average speed for all subjects. Children with dystonia moved significantly more slowly at all button sizes, and their movement speed was more sensitive to changes in button size. Therefore, part of the reduction in speed in dystonia is due to relatively greater difficulty in contacting small targets. This finding is consistent with the hypothesis of increased signal-dependent noise in children with dystonia, and we present a simple computational model that provides a possible explanation for the origin of this noise.

A review of neuropsychological and motor studies in Turner Syndrome

We reviewed the literature on Turner Syndrome (TS) from 1962 until March 2003 with respect to the following questions: Is there a consistent pattern of cognitive and/or motor dysfunction in TS girls and if so, is there an explanation for the disturbance? Many studies indicate that girls with TS have a disharmonic IQ profile: a verbal IQ that seems to be at a (nearly) normal level and a decreased PIQ. This profile remains into adulthood. Visual-spatial problems are mentioned most frequently and there is some evidence for a relationship to particular neuro-anatomical structures, hormonal dysfunction, and genotype. Although much less research has been done on motor performance in TS, there is clear evidence that it is disturbed too in TS. Many authors emphasize the interaction between somatic, psychological and social factors, but we did not find a clear theoretical framework explaining this relationship. We argue that there may be two independent problems: a visuospatial and a motor deficit possible related to specific genotypes and both have implications for functioning in daily life.