Movement disorder in Down's syndrome: a possible marker of the severity of mental handicap

"Unvoluntary" Movement Disorders: Distinguishing between Tics, Akathisia, Restless Legs, and Stereotypies

Tics, stereotypies, akathisia, and restless legs fall at different places on the spectrum of discrete, unwanted and potentially disabling motor routines. Unlike tremor, chorea, myoclonus, or dystonia, this subgroup of abnormal movements is characterized by the subject's variable ability to inhibit or release undesired motor patterns on demand. Though it may be sometimes clinically challenging, it is crucial to distinguish these "unvoluntary" motor behaviors because secondary causes and management approaches differ substantially. To this end, physicians must consider the degree of repetitiveness of the movements, the existence of volitional control, and the association with sensory symptoms, or cognitive-ideational antecedent. This review aims to summarize the current existing knowledge on phenomenology, diagnosis, and treatment of tics, stereotypies, akathisia, and restless leg syndrome.

Differentially expressed gene (DEG) based protein-protein interaction (PPI) network identifies a spectrum of gene interactome, transcriptome and correlated miRNA in nondisjunction Down syndrome

Down syndrome, a genetic disorder of known attribution reveals several types of brain abnormalities resulting in mental retardation, inadequacy in speech and memory. In this study, we have presented a consolidative network approach to comprehend the intricacy of the associated genes of Down syndrome. In this analysis, the differentially expressed genes (DEG's) were identified and the central networks were constructed as upregulated and downregulated. Subsequently, GNB5, CDC42, SPTAN1, GNG2, GNAZ, PRKACB, SST, CD44, FGF2, PHLPP1, APP, and FYN were identified as the candidate hub genes by using topological parameters. Later, Fpclass a PPI tool identified WASP gene, a co-expression interacting partner with highest network topology. Moreover, an enhanced enrichment pathway namely Opioid signaling was obtained using ClueGo, depicting the roles of the hub genes in signaling and neuronal mechanisms. The transcriptional regulatory factors and the common miRNA connected to them were identified by using MatInspector and miRTarbase. Later, a regulatory network constructed showed that PLAG, T2FB, CREB, NEUR, and GATA were the most commonly connected transcriptional factors and hsa-miR-122-5p was the most prominent miRNA. In a nutshell, these hub genes and the enriched pathway could help understand at a molecular level and eventually used as therapeutic targets for Down syndrome.

The GABAergic Hypothesis for Cognitive Disabilities in Down Syndrome

Down syndrome (DS) is a genetic disorder caused by the presence of a third copy of chromosome 21. DS affects multiple organs, but it invariably results in altered brain development and diverse degrees of intellectual disability. A large body of evidence has shown that synaptic deficits and memory impairment are largely determined by altered GABAergic signaling in trisomic mouse models of DS. These alterations arise during brain development while extending into adulthood, and include genesis of GABAergic neurons, variation of the inhibitory drive and modifications in the control of neural-network excitability. Accordingly, different pharmacological interventions targeting GABAergic signaling have proven promising preclinical approaches to rescue cognitive impairment in DS mouse models. In this review, we will discuss recent data regarding the complex scenario of GABAergic dysfunctions in the trisomic brain of DS mice and patients, and we will evaluate the state of current clinical research targeting GABAergic signaling in individuals with DS.

Down Syndrome Cognitive Phenotypes Modeled in Mice Trisomic for All HSA 21 Homologues

Down syndrome (DS), trisomy for chromosome 21, is the most common genetic cause of intellectual disability. The genomic regions on human chromosome 21 (HSA21) are syntenically conserved with regions on mouse chromosomes 10, 16, and 17 (Mmu10, Mmu16, and Mmu17). Recently, we created a genetic model of DS which carries engineered duplications of all three mouse syntenic regions homologous to HSA21. This 'triple trisomic' or TTS model thus represents the most complete and accurate murine model currently available for experimental studies of genotype-phenotype relationships in DS. Here we extended our initial studies of TTS mice. Locomotor activity, stereotypic and repetitive behavior, anxiety, working memory, long-term memory, and synaptic plasticity in the dentate gyrus were examined in the TTS and wild-type (WT) control mice. Changes in locomotor activity were most remarkable for a significant increase in ambulatory time and a reduction in average velocity of TTS mice. No changes were detected in repetitive and stereotypic behavior and in measures of anxiety. Working memory showed no changes when tested in Y-maze, but deficiency in a more challenging T-maze test was detected. Furthermore, long-term object recognition memory was significantly reduced in the TTS mice. These changes were accompanied by deficient long-term potentiation in the dentate gyrus, which was restored to the WT levels following blockade of GABAA receptors with picrotoxin (100 μM). TTS mice thus demonstrated a number of phenotypes characteristic of DS and may serve as a new standard by which to evaluate and direct findings in other less complete models of DS.

Non-neuronal cell responses differ between normal and Down syndrome developing brains

Down syndrome (DS), the most common genetic cause of mental retardation, is characterized by reduced number of neurons and delayed myelination. Though non-neuronal cells in the brain are vital for the development, survival, and function of neurons, there is a paucity of comparative studies of normal development and DS, in particular in the temporal lobe, a region of interest for cognitive decline. We evaluated immunoreactivity for CD68 (macrophage), HLA-DR (microglia), Olig2 and TPPP/p25 (oligodendroglia), and GFAP (astroglia) in the germinal matrix (GM), temporal lobe white matter (TeWM) and hippocampus from 14 weeks of gestations to newborn in 28 DS patients and 30 age-matched controls. The rate of increase of CD68 positive cells in the GM, CA1 hippocampal subregion and subiculum was significantly higher in DS. The density of Olig2 positive cells in the GM was lower in DS brains at early stages, then showed a transient increase contrasting controls. Olig2 expression increased more in the TeWM in DS, suggesting an altered pattern of oligodendrocyte progenitor generation. GFAP-immunoreactivity in DS was significantly lower in the middle pregnancy period in the TeWM and did not increase between early and middle periods in the GM compared to controls, likely reflecting a defect in astrocyte production. The altered expression of non-neuronal cell markers during normal development and DS may play a role in, or reflect, defective neurogenesis, leading to reduced number of neurons and delayed myelination in the developing DS brain. This has implications for the understanding of the mental retardation in DS patients.

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.

The impact of aging on eating, drinking, and swallowing function in people with Down's syndrome

Many people with Down's syndrome (DS) experience eating, drinking, and swallowing (EDS) difficulties, which can potentially lead to life-threatening conditions such as malnutrition, dehydration, and aspiration pneumonia. As the life expectancy of people with DS continues to improve, there is an increasing need to examine how the aging process may further affect these conditions. Published research studies have yet to address this issue; therefore, this article draws on the literature in three associated areas in order to consider the dysphagic problems that might develop in aging people with DS. The areas examined are EDS development in children and adolescents with DS, EDS changes associated with aging, and EDS changes associated with dementia of the Alzheimer's type (DAT) because this condition is prevalent in older adults with DS. This article concludes that unlike in the general population, the aging process is likely to cause dysphagic difficulties in people with DS as they get older. Therefore, it is suggested that longitudinal studies are needed to examine the specific aspects of EDS function that may be affected by aging and concomitant conditions in DS.

Stereotypic circling behavior in mice with vestibular dysfunction: asymmetrical effects of intrastriatal microinjection of a dopamine agonist

Bronx Waltzer (bv) mouse, which has been used as a model of hearing and vestibular dysfunction, shows remarkable repetitive circling behavior. This study investigated whether the behavior is caused by the asymmetry of striatal function by observing the behavior of the bv mice following microinjection of dopamine D1 agonist, A68930 into the striatum ipsilaterally and contralaterally to the preferred direction of rotation separately. High dose of the drug induced opposite effects on ipsilateral rotations by the side of injections with statistical significance (p = .0026). These results suggested that the stereotypic circling behavior involves striatum and is based on striatal asymmetry.

Neurobehavioral disorders in children, adolescents, and young adults with Down syndrome

The term dual-diagnosis refers to a person with mental retardation and a psychiatric disorder. Most children with Down syndrome (DS) do not have a psychiatric or neurobehavioral disorder. Current prevalence estimates of neurobehavioral and psychiatric co-morbidity in children with DS range from 18% to 38%. We have found it useful to distinguish conditions with a pre-pubertal onset from those presenting in the post-pubertal period, as these are biologically distinct periods each with a unique vulnerability to specific psychiatric disorders. Due to the increased recognition that psychiatric symptoms may co-occur with mental retardation, and are not inextricably linked to cognitive impairment, these conditions are considered treatable, in part, under a medical model. Improvement in physiologic regulation, emotional stability, and neurocognitive processing is one of the most elusive but fundamental goals of pharmacologic intervention in these disorders.

A Systematic Examination of Catatonia‐like Clinical Pictures in Autism Spectrum Disorders

Three studies concerning catatonia-like clinical pictures in people with autism spectrum disorders (ASDs) referred to clinics are described. The first investigated the frequencies, in children and adults with autistic disorders, of 28 specific disorders of movement, speech, and behavior similar to those occurring in chronic catatonia spectrum conditions. The second compared the frequency of these items among groups of children with, ASDs, learning disabilities, specific language impairment, and a group with typical development, respectively. The third study examined the pattern of catatonia-like deterioration occurring in a minority of adolescents and adults with ASDs. The studies demonstrated the high frequency of catatonia-like features in people with autistic disorders. There was some tendency for improvement with increasing age, especially for those with IQ 70 or over. The items were also found in children with learning disabilities and specific language disorders but significantly less often. They occurred least often in the children with typical development. Severe catatonia-like deterioration occurred in 17% of those with autistic disorders, who were aged 15 years or over when assessed at a diagnostic center. A history of passivity in social interaction and impairment of expressive language were associated with the deterioration. No clear relationship was found between a history of catatonia-like features, singly or combined, and catatonia-like deterioration. The findings pose questions for future research.

Harm avoidance, anxiety, and response to novelty in the adolescent S-100beta transgenic mouse: role of serotonin and relevance to Down syndrome

S-100beta is an astroglial-derived protein, which plays a role in brain development and maintenance, and is known to play a specific role in the regulation of growth of the serotonergic neuronal system. In humans, the gene for S-100beta is found on chromosome 21, within the region that is considered important for the phenotype of Down syndrome (DS). Thus, we have been studying a model of DS, the S-100beta transgenic mouse. In the current study, we have examined anxiety and responses to novelty in adolescent (60-90 days) animals, at a time when we have shown the animals to be relatively lacking in serotonin innervation, compared to their CD-1 nontransgenic controls. In a test for approach/avoidance, the light/dark test, the S-100beta transgenic mice animals showed no differences from control CD-1 mice. However, in the hole-board test for exploratory behavior, the S-100beta animals were found to be less responsive to the inhibiting effects of the serotonin receptor 5-HT1A agonist, buspirone. Three tests were used to measure response to novelty. In the open field, the S-100beta animals showed greater activity longer than the control animals, and in the Y-maze test, the S-100beta animals spent more time in the novel arm. In a test for novelty-induced gnawing, the S-100beta animals were also more active than control animals. All of these suggest that the S-100beta transgenic mice are slower to habituate to novelty than control animals. Finally, we tested the animals in a new procedure that we are proposing as a test for harm avoidance. In this apparatus, the S-100beta animals showed more approaches to a novel and potentially harmful object than the control mice did. These results are discussed in reference to the known lack of serotonin in the animals, and to the behavioral phenotype of DS.

Comorbid Down's syndrome, Tourette syndrome and intellectual disability: registry prevalence and developmental course

The co-occurrence of Tourette syndrome (TS) and Down's syndrome (DS) has been previously reported in the literature. In the present study, a retrospective record review was conducted using the North Dakota TS registry in order to ascertain the number of cases of TS and DS, and to develop case descriptions. We identified five cases from North Dakota. Two of these patients were simply comorbid for TS and DS. One was additionally comorbid for bipolar disorder, another for childhood disintegrative disorder and a third had a D/G group translocation. The association between DS and TS occured in 2% of TS patients. Contrary to the situation in patients with pervasive developmental disorders, the presence of TS in DS may be a negative prognostic indicator.