A solution to limitations of cognitive testing in children with intellectual disabilities: The case of fragile X syndrome

Medical Investigation of Neurodevelopmental Disorders (M.I.N.D.), Institute, University of California-Davis Medical Center, 2825 50th Street, Sacramento, CA 95817, USA.
Journal of Neurodevelopmental Disorders (Impact Factor: 3.27). 03/2009; 1(1):33-45. DOI: 10.1007/s11689-008-9001-8
Source: PubMed


Intelligence testing in children with intellectual disabilities (ID) has significant limitations. The normative samples of widely used intelligence tests, such as the Wechsler Intelligence Scales, rarely include an adequate number of subjects with ID needed to provide sensitive measurement in the very low ability range, and they are highly subject to floor effects. The IQ measurement problems in these children prevent characterization of strengths and weaknesses, poorer estimates of cognitive abilities in research applications, and in clinical settings, limited utility for assessment, prognosis estimation, and planning intervention. Here, we examined the sensitivity of the Wechsler Intelligence Scale for Children (WISC-III) in a large sample of children with fragile X syndrome (FXS), the most common cause of inherited ID. The WISC-III was administered to 217 children with FXS (age 6-17 years, 83 girls and 134 boys). Using raw norms data obtained with permission from the Psychological Corporation, we calculated normalized scores representing each participant's actual deviation from the standardization sample using a z-score transformation. To validate this approach, we compared correlations between the new normalized scores versus the usual standard scores with a measure of adaptive behavior (Vineland Adaptive Behavior Scales) and with a genetic measure specific to FXS (FMR1 protein or FMRP). The distribution of WISC-III standard scores showed significant skewing with floor effects in a high proportion of participants, especially males (64.9%-94.0% across subtests). With the z-score normalization, the flooring problems were eliminated and scores were normally distributed. Furthermore, we found correlations between cognitive performance and adaptive behavior, and between cognition and FMRP that were very much improved when using these normalized scores in contrast to the usual standardized scores. The results of this study show that meaningful variation in intellectual ability in children with FXS, and probably other populations of children with neurodevelopmental disorders, is obscured by the usual translation of raw scores into standardized scores. A method of raw score transformation may improve the characterization of cognitive functioning in ID populations, especially for research applications.

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Available from: Scott Hall, Oct 06, 2015
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    • "All children but one were in the lower end of the standard scores, indicating a floor effect. This effect is well-known in research with intellectually disabled persons (e.g., Carlier & Ayoun, 2007; Carlier & Roubertoux, 2014; Hessl et al., 2009). It arises with most intelligence tests (Reynolds & Kamphaus, 2003), which therefore typically fail to detect valid differences in the lower ranges. "
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    ABSTRACT: People spontaneously use faces to make inferences about other's personality traits or abilities, which generally lead to invalid conclusions. Here, we show first evidence that perceived variations in the facial appearance of 20 children with trisomy 21 (t21) influence how they are perceived in terms of intelligence (or intellectual disability), the more “trisomic” faces being rated as less intelligent (or more intellectually disabled). Despite high degrees of inter-rater agreement (80 raters), these inferences were unrelated to individuals’ actual test scores which were also unrelated to perceived facial appearance. All these findings indicate that social inferences about intelligence based on facial appearance are unreliable even in groups characterized by a genetic disorder such as t21.
    Research in Developmental Disabilities 12/2014; 35(12):3598-3605. DOI:10.1016/j.ridd.2014.09.003 · 3.40 Impact Factor
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    • "The fact that the relationship between cognitive ability and ASD symptomatology differs for FXS and non-syndromic ASD complicates any comparison between the two disorders because, on average, cognitive abilities are more limited in individuals with FXS than in individuals with non-syndromic ASD; for example, more than 90% of males with FXS have IQs in the range of intellectual disability (Hessl et al., 2009) compared to 16–38% of males with non-syndromic ASD (Baio, 2012; Ryland et al., 2014). Unless differences in cognitive ability are controlled in comparisons between FXS and non-syndromic ASD or between individuals with FXS with and without comorbid ASD, it is impossible to unambiguously ascribe differences in ASD symptom profiles, correlates, or developmental trajectories to etiological group or to cognitive ability. "
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    ABSTRACT: Autism spectrum disorder (ASD) is a common comorbid condition in people with fragile X syndrome (FXS). It has been assumed that ASD symptoms reflect the same underlying psychological and neurobiological impairments in both FXS and non-syndromic ASD, which has led to the claim that targeted pharmaceutical treatments that are efficacious for core symptoms of FXS are likely to be beneficial for non-syndromic ASD as well. In contrast, we present evidence from a variety of sources suggesting that there are important differences in ASD symptoms, behavioral and psychiatric correlates, and developmental trajectories between individuals with comorbid FXS and ASD and those with non-syndromic ASD. We also present evidence suggesting that social impairments may not distinguish individuals with FXS with and without ASD. Finally, we present data that demonstrate that the neurobiological substrates of the behavioral impairments, including those reflecting core ASD symptoms, are different in FXS and non-syndromic ASD. Together, these data suggest that there are clinically important differences between FXS and non-syndromic ASD that are masked by reliance on the categorical diagnosis of ASD. We argue for use of a symptom-based approach in future research, including studies designed to evaluate treatment efficacy.
    Frontiers in Genetics 10/2014; 5. DOI:10.3389/fgene.2014.00355
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    • "Although FXS affects both males and females, it is more common in males, and males are more severely affected on average. Over 95% of males with FXS have cognitive abilities within the intellectual disability range (IQ of < 70; Hessl et al., 2009). In addition, males with FXS often display a behavioral phenotype that includes gaze avoidance, repetitive behaviors, inattention, hyperarousal, and social anxiety (Hessl et al., 2006; Wolff et al., 2012). "
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    ABSTRACT: We examined the visual processing of a social learning stimulus and the ways in which visual attention was distributed to objects as well as to the examiner's face during word learning under conditions that varied only in the presence or absence of a label. The goal of the current study, then, was to evaluate the effects of differentially providing pointing and labeling during exposure to a novel target object in males with fragile X syndrome (FXS) (n=14, ages 4.33-10.02), autism spectrum disorder (ASD) (n=17, ages 4.04-10.4), or typical development (TD) (n=18, ages 2.05-5.33). In particular, the present study examined attention to the examiner's face as well as target and distracter objects that were presented as video stimuli. An eye-tracker captured gaze to the video stimuli as they were shown in order to examine the way in which children with FXS, ASD, or TD distributed their gaze toward the examiner and the objects. Results indicated that no group showed increased gaze toward the target object compared to the distracter object. However, results revealed that participants with FXS showed significantly increased face gaze compared to the novel objects, whereas children with ASD and TD both showed similar amounts of relative gaze toward the face and objects. Furthermore, the act of pointing at the target object was found to increase gaze toward the target objects compared to when there was no pointing in all groups. Together, these findings suggest that social cues like those employed in a word-learning task, when presented with video, may relate to gaze in FXS in context- or task-dependent ways that are distinct from those expected during live interaction.
    Research in Developmental Disabilities 07/2014; 35(11):2658-2672. DOI:10.1016/j.ridd.2014.06.021 · 3.40 Impact Factor
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