Psychometric properties of inhibitory control measures among youth with Down syndrome.

BACKGROUND: Inhibitory control measures have been commonly used when assessing individuals with Down syndrome. However, minimal attention has been devoted to evaluating the appropriateness of specific assessments for use in this population, potentially leading to erroneous conclusions. This study aimed to examine the psychometric properties of measures of inhibitory control among youth with Down syndrome. We sought to examine the feasibility, presence of floor or practice effects, test-retest reliability, convergent validity and correlations with broader developmental domains of a set of inhibitory control tasks. METHODS: A sample of 97 youth with Down syndrome aged 6 to 17 years old participated in verbal and visuospatial tasks of inhibitory control including the Cat/dog Stroop, Neuropsychological Assessment Second Edition (NEPSY-II) Statue, National Institutes of Health (NIH) Toolbox Cognition Battery (TCB) Flanker, Leiter-3 Attention Sustained, and the Test of Attentional Performance for Children (KiTAP) Go/No-go and Distractibility subtests. Youth also completed standardised assessments of cognition and language, and caregivers completed rating scales. Psychometric properties on the tasks of inhibitory control were evaluated against a priori criteria. RESULTS: Apart from demonstrating negligible practice effects, adequate psychometric properties were not observed for any inhibitory control measure within the current sample's age range. One task with low working memory demands (NEPSY-II Statue) generally had better psychometric properties than the other tasks assessed. Subgroups of participants with an IQ greater than 30 and age more than 8 years were shown to be more likely to be able to complete the inhibition tasks. CONCLUSIONS: Findings suggest better feasibility for analogue tasks rather than computerised assessments of inhibitory control. Given the weak psychometrics of several common measures, future studies are required to evaluate other inhibitory control measures, specifically those with reduced working memory demands for youth with Down syndrome. Recommendations for use of the inhibitory control tasks among youth with Down syndrome are provided.

Reliability of parent report measures of behaviour in children with Down syndrome.

BACKGROUND: Behavioural problems are common among children with Down syndrome (DS). Tools to detect and evaluate maladaptive behaviours have been developed for typically developing children and have been evaluated for use among children with intellectual and developmental disabilities. However, these measures have not been evaluated for use specifically in children with DS. This psychometric evaluation is important given that some clinically observed behaviours are not addressed in currently available rating scales. The current study evaluates the psychometric properties of the Child Behavior Checklist (CBCL), a commonly used screening tool developed for typically developing children and commonly used with children with intellectual and developmental disabilities. METHODS: The study investigated the psychometric properties of the CBCL among school-aged children with DS, including an assessment of the rate of detecting behaviour problems, concerns with distribution, internal consistency, inter-rater reliability and convergent and discriminant validity with the Aberrant Behavior Checklist and Nisonger Child Behavior Rating Form. Caregivers of 88 children with DS aged 6-18 years rated their child's behaviour with the CBCL, Aberrant Behavior Checklist and Nisonger Child Behavior Rating Form. Teachers completed the Teacher Report Form. RESULTS: About one-third of children with DS were reported to exhibit behaviours of clinical concern on the total score of the CBCL. Internal consistency for CBCL sub-scales was poor to excellent, and inter-rater reliability was generally acceptable. The sub-scales of the CBCL performed best when evaluating convergent validity, with variable discriminant validity. Normative data conversions controlled for age and gender differences in this sample. CONCLUSIONS: The study findings suggest that, among children with DS, some CBCL sub-scales generally performed in a psychometrically sound and theoretically appropriate manner in relation to other measures of behaviour. Caution is warranted when interpreting specific sub-scales (Anxious/Depressed, Somatic Complaints and Thought Problems). The CBCL can continue to be used as a screening measure when evaluating behavioural concerns among children with DS, acknowledging poor discriminant validity and the possibility that key behaviour concerns in DS may not be captured by the CBCL screen.

Impact of sleep on executive functioning in school-age children with Down syndrome.

BACKGROUND: Sleep problems have an impact on executive functioning in the general population. While children with Down syndrome (DS) are at high risk for sleep problems, the impact of these sleep problems on executive functioning in school-age children with DS is less well documented. Our study examined the relationship between parent-reported and actigraphy-measured sleep duration and sleep quality with parent and teacher reports and neuropsychology assessments of executive functioning among school-age children with DS. METHOD: Thirty school-age children with DS wore an actigraph watch for a week at home at night. Their parent completed ratings of the child's sleep during that same week. Children completed a neuropsychology assessment of their inhibitory control, ability to shift and working memory. Their parents and teachers completed rating scales to assess these same constructs of executive functioning. RESULTS: Parent reports of restless sleep behaviours on the Children's Sleep Habits Questionnaire (CSHQ), but not actigraph-measured sleep period or efficiency, were predictive of parent reports of concerns with inhibitory control, shifting and working memory, and of teacher reports of inhibitory control. No measure of sleep was predictive of executive functioning as measured by the neuropsychology assessment. CONCLUSION: The study findings corroborate the preliminary literature that parent-reported sleep problems are related to executive functioning in school-age children with DS, particularly in the area of inhibitory control across home and school. These findings have implications for understanding contributing factors to academic performance and school behaviour in school-age children with DS.

Convergent validity of actigraphy with polysomnography and parent reports when measuring sleep in children with Down syndrome.

BACKGROUND: There is a need for rigorous measures of sleep in children with Down syndrome as sleep is a substantial problem in this population and there are barriers to obtaining the gold standard polysomnography (PSG). PSG is cost-prohibitive when measuring treatment effects in some clinical trials, and children with Down syndrome may not cooperate with undergoing a PSG. Minimal information is available on the validity of alternative methods of assessing sleep in children with Down syndrome, such as actigraphy and parent ratings. Our study examined the concurrent and convergent validity of different measures of sleep, including PSG, actigraphy and parent reports of sleep among children with Down syndrome. METHOD: A clinic (n = 27) and a community (n = 47) sample of children with Down syndrome were examined. In clinic, children with Down syndrome wore an actigraph watch during a routine PSG. In the community, children with Down syndrome wore an actigraph watch for a week at home at night as part of a larger study on sleep and behaviour. Their parent completed ratings of the child's sleep during that same week. RESULTS: Actigraph watches demonstrated convergent validity with PSG when measuring a child with Down syndrome's total amount of sleep time, total wake time after sleep onset and sleep period efficiency. In contrast, actigraph watches demonstrated poor correlations with parent reports of sleep, and with PSG when measuring the total time in bed and total wake episodes. Actigraphy, PSG and parent ratings of sleep demonstrated poor concurrent validity with clinical diagnosis of obstructive sleep apnoea. CONCLUSION: Our current data suggest that actigraph watches demonstrate convergent validity and are sensitive to measuring certain sleep constructs (duration, efficiency) in children with Down syndrome. However, parent reports, such as the Children's Sleep Habits Questionnaire, may be measuring other sleep constructs. These findings highlight the importance of selecting measures of sleep related to target concerns.

Links between sleep and daytime behaviour problems in children with Down syndrome.

BACKGROUND: In the general population, sleep problems have an impact on daytime performance. Despite sleep problems being common among children with Down syndrome, the impact of sleep problems on daytime behaviours in school-age children with Down syndrome is an understudied topic. Our study examined the relationship between parent-reported and actigraphy-measured sleep duration and sleep quality with parent and teacher reports of daytime behaviour problems among school-age children with Down syndrome. METHOD: Thirty school-age children with Down syndrome wore an actigraph watch for a week at home at night. Their parent completed ratings of the child's sleep during that same week. Their parent and teacher completed a battery of measures to assess daytime behaviour. RESULTS: Parent reports of restless sleep behaviours on the Children's Sleep Habits Questionnaire, but not actigraph-measured sleep efficiency, was predictive of parent and teacher behavioural concerns on the Nisonger Child Behaviour Rating Form and the Vanderbilt ADHD Rating Scales. Actigraph-measured sleep period and parent-reported sleep duration on the Children's Sleep Habits Questionnaire was predictive of daytime parent-reported inattention. Actigraph-measured sleep period was predictive of parent-reported hyperactivity/impulsivity. CONCLUSION: The study findings suggest that sleep problems have complex relationships to both parent-reported and teacher-reported daytime behaviour concerns in children with Down syndrome. These findings have implications for understanding the factors impacting behavioural concerns and their treatment in school-age children with Down syndrome.

Reliability of parent report measures of sleep in children with Down syndrome.

BACKGROUND: Behavioural sleep disturbances are common among children with Down syndrome (DS). However, tools used to detect and evaluate behavioural sleep disturbances were developed for typically developing children and have not been evaluated for use among children with DS. The current study evaluates the psychometric properties of three measures of behavioural sleep disturbances that are currently being used with children with intellectual and developmental disabilities, including children with DS. METHOD: Caregivers of 30 children with DS rated their child's sleep with the Behavioral Evaluation of Disorders of Sleep (BEDS), Children's Sleep Habits Questionnaire (CSHQ) and Sleep Disturbances Scale for Children (SDSC). Caregivers also provided information on sleep diagnoses and completed a 7-night sleep and behaviour diary. RESULTS: The study investigated the rate of detecting sleep problems, internal consistency, and convergent and concurrent validity of the BEDS, CSHQ and SDSC. Children with DS were reported to exhibit behavioural sleep disturbances at different rates depending on the measure used; 0% BEDS, 79.3% CSHQ and 17.2% SDSC. Internal consistency was comparable for all three measures for their total scores. However, when evaluating the internal consistency of subscale scores, those on the CSHQ and SDSC performed more strongly. The subscales of the CSHQ performed best when evaluating convergent and concurrent validity, with the SDSC subscales performing moderately well. CONCLUSION: The study findings suggest that, among children with DS, the CSHQ and its subscales performed in a psychometrically sound and theoretically appropriate manner in relation to other measures of sleep, medical history of sleep problems, and daily reports of sleep and associated behaviours. The SDSC performed moderately well. When evaluating behavioural sleep disturbances among children with DS, the CSHQ is recommended based on its stronger psychometric properties.

Targeted deletion of the cytosolic Cu/Zn-superoxide dismutase gene (Sod1) increases susceptibility to noise-induced hearing loss.

Reactive oxygen species (ROS) such as superoxide, peroxide and hydroxyl radicals are generated during normal cellular metabolism and are increased in acute injury and in many chronic disease states. When their production is inadequately regulated, ROS accumulate and irreversibly damage cell components, causing impaired cellular function and death. Antioxidant enzymes such as superoxide dismutase (SOD) play a vital role in minimizing ROS levels and ROS-mediated damage. The cytosolic form of Cu/Zn-SOD appears specialized to remove superoxide produced as a result of injury. 'Knockout' mice with targeted deletion of Sod1, the gene that codes for Cu/Zn-SOD, develop normally but show enhanced susceptibility to central nervous system injury. Since loud noise is injurious to the cochlea and is associated with elevated cochlear ROS, we hypothesized that Sod1 knockout mice would be more susceptible to noise-induced permanent threshold shifts (PTS) than wild-type and heterozygous control mice. Fifty-nine mice (15 knockout, 29 heterozygous and 15 wild type for Sod1) were exposed to broad-band noise (4.0-45.0 kHz) at 110 dB SPL for 1 h. Hearing sensitivity was evaluated at 5, 10, 20 and 40 kHz using auditory brainstem responses before exposure and 1, 14 and 28 days afterward. Cu/Zn-SOD deficiency led to minor (0-7 dB) threshold elevations prior to noise exposure, and about 10 dB of additional noise-induced PTS at all test frequencies, compared to controls. The distribution of thresholds at 10 and 20 kHz at 28 days following exposure contained three modes, each showing an effect of Cu/Zn-SOD deficiency. Thus another factor, possibly an additional unlinked gene, may account for the majority of the observed PTS. Our results indicate that genes involved in ROS regulation can impact the vulnerability of the cochlea to noise-induced hearing loss.

Hindlimb motor neurons require Cu/Zn superoxide dismutase for maintenance of neuromuscular junctions.

The role of oxidative damage in neurodegenerative disease was investigated in mice lacking cytoplasmic Cu/Zn superoxide dismutase (SOD), created by deletion of the SOD1 gene (SOD1(-/-)). SOD1(-/-) mice developed a chronic peripheral hindlimb axonopathy. Mild denervation of muscle was detected at 2 months, and behavioral and physiological motor deficits were present at 5-7 months of age. Ventral root axons were shrunken but were normal in number. The somatosensory system in SOD1(-/-) mice was mildly affected. SOD1(-/-) mice expressing Cu/Zn SOD only in brain and spinal cord were generated using transgenic mice expressing mouse SOD1 driven by the neuron-specific synapsin promoter. Neuron-specific expression of Cu/Zn SOD in SOD1(-/-) mice rescued motor neurons from the neuropathy. Therefore, Cu/Zn SOD is not required for normal motor neuron survival, but is necessary for the maintenance of normal neuromuscular junctions by hindlimb motor neurons.

Superoxide-mediated cytotoxicity in superoxide dismutase-deficient fetal fibroblasts.

To investigate the roles of CuZn superoxide dismutase (CuZnSOD) and Mn superoxide dismutase (MnSOD) in oxygen radical-mediated cytotoxicity and to distinguish the actions of these two enzymes, fetal fibroblasts were derived from mouse fetuses that are either deficient in CuZnSOD (Sod1-/+ and -/-) or MnSOD (Sod2-1+ and -/-) for in vitro studies. Whereas the phenotype of the Sod1 mutant animals did not differ from that of their normal littermates, the growth of Sod1-/- fetal fibroblasts was only 25% of that of the -/+ and +/+ cells. On the other hand, although almost all homozygous Sod2 mutant animals (-/-) died within 10 days after birth, cultivation of Sod2-/- fetal fibroblasts was possible and their growth was about 60% that of -/+ and +/+ cells. When cultured cells were subjected to treatment with paraquat to assess their ability to grow in the presence of high levels of superoxide radicals, Sod1-/- cells were 80 times more sensitive and Sod2-/- cells were 12 times more sensitive to paraquat than wild-type cells. In addition, whereas the loss of 50% CuZnSOD rendered Sod1-/+ cells almost twice more sensitive to paraquat than +/+ cells, loss of 50% MnSOD had no effect on paraquat sensitivity. Our results suggest that CuZnSOD-deficient cells are more sensitive to oxygen toxicity than are MnSOD-deficient cells, that paraquat causes free radical-induced damage in both the mitochondria and cytoplasm, and that SOD compartmentalized in the cytosol cannot compensate for the loss of SOD in the mitochondria and vice versa.

Reduction of CuZn-superoxide dismutase activity exacerbates neuronal cell injury and edema formation after transient focal cerebral ischemia.

Apoptotic neuronal cell death has recently been associated with the development of infarction after cerebral ischemia. In a variety of studies, CuZn-superoxide dismutase (CuZn-SOD) has been shown to protect the brain from ischemic injury. A possible role for CuZn-SOD-related modulation of neuronal viability is suggested by the finding that CuZn-SOD inhibits apoptotic neuronal cell death in response to some forms of cellular damage. We evaluated this possibility in the model of transient focal cerebral ischemia in mice bearing a disruption of the CuZn-SOD gene (Sod1). Homozygous mutant (Sod1 -/-) mice had no detectable CuZn-SOD activity, and heterozygous mutants (Sod1 +/-) showed a 50% decrease compared with wild-type mice. Sod1 -/- mice showed a high level of blood-brain barrier disruption soon after 1 hr of middle cerebral artery occlusion and 100% mortality at 24 hr after ischemia. Sod1 +/- mice showed 30% mortality at 24 hr after ischemia, and neurological deficits were exacerbated compared with wild-type controls. The Sod1 +/- animals also had increased infarct volume and brain swelling, accompanied by increased apoptotic neuronal cell death as indicated by the in situ nick-end labeling technique to detect DNA fragmentation and morphological criteria. These results suggest that oxygen-free radicals, especially superoxide anions, are an important factor for the development of infarction by brain edema formation and apoptotic neuronal cell death after focal cerebral ischemia and reperfusion.

Proteasome inhibition enhances the stability of mouse Cu/Zn superoxide dismutase with mutations linked to familial amyotrophic lateral sclerosis.

Point mutations occurring within the Cu/Zn superoxide dismutase (SOD1) gene have been implicated in the etiology of some cases of familial amyotrophic lateral sclerosis (FALS). In order to better understand the functional consequences of these mutations, we have introduced FALS mutations into the mouse SOD1 gene and studied the expression of the mutant templates in stably transformed cell lines. Pulse-chase analyses of lysates derived from cell lines stably expressing the Cu/Zn SOD isoforms indicate that the FALS mutant Cu/Zn SOD proteins are turned over more rapidly than wild-type SOD. Protease inhibitors specific for the major intracellular proteolytic activities were used to characterize the degradative pathways involved in the turnover of mutant Cu/Zn SOD. Inhibition of the chymotrypsin-like activity of the proteasome (also known as multicatalytic proteinase or ubiquitin, ATP-dependent proteinase) by a synthetic dipeptide aldehyde led to a significant increase in levels of the mutant Cu/Zn SOD implicating this proteolytic pathway in the turnover of the FALS mutant SOD proteins.

Motor neurons in Cu/Zn superoxide dismutase-deficient mice develop normally but exhibit enhanced cell death after axonal injury.

The discovery that some cases of familial amyotrophic lateral sclerosis (FALS) are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) has focused much attention on the function of SOD1 as related to motor neuron survival. Here we describe the creation and characterization of mice completely deficient for this enzyme. These animals develop normally and show no overt motor deficits by 6 months in age. Histological examination of the spinal cord reveals no signs of pathology in animals 4 months in age. However Cu/Zn SOD-deficient mice exhibit marked vulnerability to motor neuron loss after axonal injury. These results indicate that Cu/Zn SOD is not necessary for normal motor neuron development and function but is required under physiologically stressful conditions following injury.

Structure and organization of amplified DNA on double minutes containing the mdm2 oncogene.

We have been studying a transformed derivative of a mouse fibroblast line (3T3DM) that stably maintains double minute chromosomes (DMs). In this report we describe a comprehensive analysis of the structure of the DMs within this cell line, utilizing a combination of long-range mapping via pulsed-field gel electrophoresis, screening of DM-enriched genomic libraries, and DM sizing using contour-clamped homogeneous electric field (CHEF) gel electrophoresis. Our data indicate that the minute particles in these cells exist as a homogeneous population of circular molecules, roughly 4 Mb in size, upon which three genes are amplified. One of these is the mdm2 oncogene, which has also been found to be amplified in a number of human sarcomas. Further, we present evidence that these three genes are arranged as two identical inverted repeat units linked by spacer regions of heterogeneous size. This work has led to the first model for the structure of an entire double minute particle containing an amplified oncogene; this model provides clues to later events occurring in the gene amplification process in tumor cells.

Induction of NGF by isoproterenol, 4-methylcatechol and serum occurs by three distinct mechanisms.

Evidence is provided that isoproterenol, 4-methylcatechol and serum induce NGF by three separate mechanisms. Isoproterenol and 4-methylcatechol induced NGF and NGF mRNA in mouse fibroblast L929 cells in either the presence or absence of serum. Propranolol prevented NGF induction by isoproterenol, but not by 4-methylcatechol or serum. All possible combinations of these inducers resulted in additive increases in the levels of NGF and NGF mRNA.

An S1 nuclease-sensitive homopurine/homopyrimidine domain in the c-Ki-ras promoter interacts with a nuclear factor.

To gain insight into the normal controls mediating expression of the c-Ki-ras protooncogene, we have identified DNA sequence elements within its promoter that are essential for transcriptional activity. Transient expression assays using the bacterial chloramphenicol acetyltransferase gene were used initially to localize regions directing primary promoter function. Stepwise deletion of 5' promoter sequences resulted in a gradual decrease in the ability to drive transcription of the reporter gene, suggesting that this promoter is composed of multiple cis-acting elements. Gel mobility-shift and DNase protection studies involving a 166-base-pair DNA fragment allowed the identification of protein-binding sites corresponding to these multiple regulatory elements. One element demonstrating particular transcriptional influence exists as a homopurine/homopyrimidine-rich region that in vitro exhibits S1 nuclease sensitivity and binds at least one nuclear protein. Data from competition binding experiments suggest that this nuclear factor may be influential in the regulation of other essential growth-control genes as well.

Transcriptional activation of cKi-ras proto-oncogene resulting from retroviral promoter insertion.

Enhanced expression of the cKi-ras proto-oncogene in a bone marrow-derived mouse cell line, 416B, has been shown to be associated with the integration of Friend viral DNA into the cellular gene. Here we report the results of experiments designed to clarify the molecular mechanism responsible for the cKi-ras overexpression. Based on primer extension analyses and DNA sequencing of cKi-ras cDNA clones, we have obtained evidence that the 416B cells contain viral-host chimaeric transcripts that initiate within the 3' long terminal repeat (LTR) of the integrated provirus. Processing of the transcripts from the rearranged cKi-ras gene includes an unexpected splicing event associated with the fortuitous creation of a cryptic donor splice site at the junction between the proviral and cellular DNA sequences. These data demonstrate that enhanced cKi-ras expression in the 416B cells results from a retroviral promoter insertion mechanism of transcriptional activation.

The upstream promoter of the human LDL receptor gene does not contain a cyclic AMP response element.

Fusion genes containing segments of the promoter region of the human LDL receptor gene and the coding sequence of the bacterial enzyme, chloramphenicol acetyltransferase (CAT), were introduced into JEG-3 human choriocarcinoma cells. Constructs containing 177 base pairs of 5'-flanking DNA (pLDLR-CAT 234) or 6500 base pairs (pLDLR-CAT 6500) promoted CAT activity in transient expression assays. Although both pLDLR-CAT 234 and pLDLR-CAT 6500 contain sequences related to the recently reported consensus sequence for cyclic AMP responsiveness, treatment of the transfected JEG-3 cells with 8-bromo-cAMP did not increase CAT activity. The cyclic AMP analog did, however, stimulate steroidogenesis and hCG secretion and increase CAT activity in cells transfected with p18X2SV1CAT, which contains two copies of an 18 base pair sequence corresponding to the cAMP-responsive element of the human alpha chorionic gonadotropin gene.

Structural and functional characterization of the promoter region of the mouse c-Ki-ras gene.

We isolated and characterized the 5' region of the mouse c-Ki-ras gene, including a 5' untranslated exon (exon 0). These studies used genetic material from Y1 mouse adrenocortical tumor cells in which the c-Ki-ras gene is amplified and overexpressed. Our data demonstrate that transcription initiates at multiple sites, predicting size heterogeneity at the 5' ends of the c-Ki-ras mRNAs. Using transient expression assays, we identified a genomic fragment within the 5' region which exhibits bidirectional promoter activity.