Habilidades numéricas em crianças com microdeleções na região 22Q: estudo de grupo e análise de caso

Abstract

Chromosome 22 was the first to be sequenced by the Human Genome Project and changes in its structure can generate numerous health conditions. The overall objective of the study is to investigate the numerical abilities in individuals with microdeletions on chromosome 22, specifically velocardiofacial syndrome (Del22q11.2) and distal microdeletion of LCR22- 4 to LCR22-5 region. The first study consists of a comparative analysis of basic numerical skills in three groups of children aged between 8 and 14 years: 12 individuals with Del22q11.2, 12 children with low cognitive abilities (LCA) and 12 children with typical development (TD). All children were evaluated by a simple reaction time task and symbolic and non-symbolic comparison of magnitudes tasks. To estimate the accuracy of the approximate number system (number sense), the Weber fraction (w) was calculated from the non-symbolic magnitude comparison task. The Del22q11.2 group showed significantly higher performance in w, when compared with the other groups. Importantly, no significant differences were found in w between TD and LCA groups. The observed impairment of number sense in individuals with Del22q11.2 can not be explained by deficits in processing speed, because no significant differences were found between groups. These results suggest that the low accuracy to differentiate quantities should be added to the behavioral phenotype of Del22q11.2. The absence of impaired acuity in LCA group is consistent with the hypothesis that number sense is a relatively specific and autonomous domain. The second study consists of a case study whose objective is to evaluate the numerical skills of a pre-teen with dyscalculia phenotype and genotype characterized by a distal microdeletion on chromosome 22. It is noteworthy that she was identified from a population-based study whose objective was to assess the genotype of children with learning difficulties in mathematics. Furthermore, the case study suggested that the difficulties in learning mathematics can be explained by a deficit in the ability to differentiate quantities measured by the Weber fraction. These results showed that the microdeletion on chromosome 22 contributes to the development of dyscalculia and it is related to an important cognitive mechanism, the deficit to differentiate quantities, measured by the Weber fraction.