COGNITIVE CORRELATES OF MATHEMATICAL DISABILITIES IN CHILDREN WITH VELO-CARDIO-FACIAL SYNDROME

Summary: Cognitive correlates of mathematical disabilities in children with velo-cardio-facial syndrome: Children with Velo-Cardio-Facial Syndrome (VCFS) consistently show mathematical disabilities (MD). At the neuropsychological level, it is important to know which general cognitive deficits underlie these MD. Therefore, we examined various mathematical abilities, working memory, rapid automatized naming and processing speed in 25 children with VCFS and 25 carefully selected matched controls. Children with VCFS showed a reduced ability to solve addition and subtraction problems and performed less accurately on multidigit arithmetic and word problem solving. There were no group differences on the general cognitive measures, except that children with VCFS performed higher than controls on the phonological loop tasks. To conclude, the administered general cognitive competencies could not give a satisfactory account of the MD in VCFS. Key-words: 22q11 Deletion Syndrome - Dyscalculia - Cognitive phenotype - Working memory INTRODUCTION In recent years, the investigation of the cognitive phenotype of disorders of a known genetic origin that have a high prevalence of mathematical disabilities (MD) has gained growing interest among researchers. MD have been described as a core feature in several genetic disorders, like Turner syndrome or Fragile-X syndrome (40). In this study, we focus on another common genetic disorder with a high prevalence of MD, the Velo-Cardio-Facial Syndrome (VCFS). We aimed to further characterize the cognitive processes involved in the development of the MD in VCFS, which provides a crucial basis for designing effective educational interventions for these children. VCFS (53) is the most frequent known microdeletion syndrome with an incidence of 1 in 4000 live births (49). It is caused by a sub-microscopic deletion in chromosome 22q11, which is detectable with 100% accuracy by means of modern molecular genetic techniques (i.e. Fluorescence in situ Hybridisation - FISH) (50). This deletion mainly occurs as a de novo event, but familial inheritance is found in approximately 15% of the patients (60). Although the clinical presentation of VCFS is quite variable, its major characteristics are velopharyngeal abnormalities, congenital heart anomalies, mild facial dysmorphism and learning disabilities (60). Intellectual abilities of children with VCFS are in general lower than average (mean IQ approximately 75) with approximately 60% of the children scoring in the borderline to normal intellectual range (IQ > 70) and approximately 40% having (mild) mental retardation. The IQ profile is often characterized by a Verbal IQ (VIQ) - Performance IQ (PIQ) discrepancy, in favour of the VIQ(15). During the last decade, considerable progress has been made in describing the cognitive phenotype of this genetic condition (for a review see 16). It has been consistently documented that school-aged children with VCFS show normal scores for reading (decoding) and spelling but have remarkable deficits in mathematics (43, 59, 64). Recently, efforts have been made to delineate more carefully the MD in these children (17,18,55), revealing subtle difficulties in low-level number processing, like counting dots and comparing numbers. At the neuropsychological level, it is important to know which general cognitive skills underlie the MD seen in children with VCFS. In general, suggested cognitive correlates of MD include difficulties in working memory and difficulties in retrieving information from long-term memory (LTM) (27,37). An impairment in working memory has been frequently reported in children with MD (9,42,46,62). Most of these studies used the well known multi-component model of working memory originally developed by Baddeley and Hitch (3). At the core of this model is the central executive, responsible for the control, regulation and monitoring of complex cognitive processes. …