Patterns of developmental dyscalculia with or without dyslexia.

This study has been conducted in order to investigate the extent to which some characteristics of dyscalculia may be common to dyslexia. Seven multiple single-cases were studied: two children with dyslexia only, two with dyscalculia only, and three more children with comorbidity of dyslexia and dyscalculia. Each participant was assessed with a standardized comprehensive battery of arithmetical, reading, and cognitive tests. We observed that a clinical impairment in mental and written calculations, arithmetical facts retrieval, number comparison, number alignment, and identification of arithmetical signs may appear with a normal reading capacity and independently of a short-term verbal memory deficit. These findings add convergent support to the evidence mainly obtained from group comparisons that the more distinctive characteristics of dyscalculia are functionally independent of dyslexia.