Individuals with Prader-Willi Syndrome and Others with Early-onset Morbid Obesity Share Similar Relative Strengths in Cognition and Achievement

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Krista A. Schwenk^1,2, Jennifer Miller², John H. Kranzler¹, Daniel J. Driscoll²

College of Education¹ and Department of Pediatrics², University of Florida

Introduction: Individuals with PWS have been described as showing mild to moderate mental retardation and multiple severe learning disabilities with relative weaknesses in short-term memory and mathematical skills and relative strengths in reading skills and on tasks that assess attention to visual detail, visual-motor coordination, perceptual planning, and spatial organization. Dykens and colleagues (J. Am. Acad. Child Adolesc. Psychiatry, 1992) found that the mean level of overall achievement for individuals with PWS was approximately 2 years above their mean mental processing composite age score. However, Whittington et al. (J. of Intellectual Disability Research, 2004) reported that levels of achievement were lower than what was predicted based on IQ among individuals with PWS. Furthermore, our group (Miller et al., J. Peds, 2006) recently demonstrated that individuals with early-onset morbid obesity, on average, have significantly lower general intellectual ability and lower achievement than normal sibling controls.

Methods: The Woodcock-Johnson Tests of Cognitive Abilities, Third Edition (WJIII-Cog) and the Woodcock-Johnson Tests of Achievement, Third Edition (WJIII-TA) were used to determine the extent to which individuals with PWS, early-onset morbid obesity (EMO) of unknown etiology, and their normal sibling control participants reached the attainments predicted by their IQ. In addition, the relative strengths and weaknesses of the 3 groups (PWS, EMO, and controls) were investigated. Extensive genetic testing was conducted on both the PWS and EMO participants.

Results: All 3 groups scored higher on their overall achievement score (TIA) than their IQ, but the difference between these scores was only significant for the PWS group (PWS: TIA = 67, IQ = 63; EMO: TIA = 79, IQ = 75; Control: TIA = 109, IQ = 108). Mean differences between the PWS and EMO groups were not significantly different on the Cognitive Efficiency and Phonemic Awareness clusters. The PWS and EMO groups scored significantly higher on the Verbal Ability, Thinking Ability, and Phonemic Awareness cluster scores of the WJIII-Cog than predicted by their overall IQ. Moreover, Phonemic Awareness was a particular strength for both the PWS and EMO groups.

Mean overall achievement between the PWS and EMO groups was not significantly different. In addition, both the PWS and EMO groups scored significantly higher on the Oral Language and Academic Skills cluster scores of the WJIII-TA than their TIA.

Conclusions: Results indicate that individuals with PWS and EMO share many similarities in terms of their cognitive abilities and achievement scores. In particular, both groups scored significantly higher on the Phonemic Awareness cluster compared to their IQ and on the Oral Language cluster compared to their TIA. Our results indicate that individuals with PWS and others with EMO have relative strengths in linguistic competency, listening ability, and comprehension. We are currently performing very detailed anatomic measurements of brain morphology from head MRIs to better understand the mechanisms of the strengths and weaknesses in cognition and achievement in individuals with PWS and EMO, with particular attention to the auditory/speech cortex.