Evaluation of narrative abilities in patients suffering from Duchenne Muscular Dystrophy.

The present work investigated cognitive, linguistic and narrative abilities in a group of children suffering from Duchenne Muscular Dystrophy, an allelic X-linked recessive disorder caused by mutations in the gene encoding dystrophin. The patients showed mildly reduced IQ with lower Verbal than Performance Intelligence Quotient and were mildly affected in visual attention and short-term memory processing. At the linguistic assessment, neither receptive (word comprehension) nor expressive (naming tasks and fluency) lexical abilities were impaired. However, their narratives were qualitatively inferior with respect to those produced by a group of typically developing children. Their speech samples were characterized by the presence of fewer verbs and complete sentences. It is suggested that the reduced production of complete sentences is due to a selective problem in verb argument structure generation. Since the lack of dystrophin is assumed to produce effects on the maturation of the cerebellum, whose involvement has been recently suggested in verb and syntactic processing, these findings may lend indirect support to the hypothesis of a cerebellar-cortical circuit specialized in verb and sentence production.

Indicators of theory of mind in narrative production: a comparison between individuals with genetic syndromes and typically developing children.

It is a matter of debate whether the development of theory of mind (ToM) depends on linguistic development or is, rather, an expression of cognitive development. The study of genetic syndromes, which are characterized by intellectual impairment as well as by different linguistic profiles, may provide useful information with respect to this issue. The present study compares indicators of ToM in the narrative production of individuals with Cornelia de Lange syndrome, Down syndrome, Williams syndrome and typically developing children, matched on sex and mental age. Statistical comparisons of data obtained from a qualitative analysis of the narrative production of the different groups confirm the presence of distinctive patterns, mainly related to the effective use of personal pronouns. The analysis of correlations among story-telling variables and other cognitive and linguistic variables suggests that the relationship between language development, cognitive development, and the emergence of ToM cannot be reduced to unidirectional causal links.

Association of short-term memory with a variant within DYX1C1 in developmental dyslexia.

A substantial genetic contribution in the etiology of developmental dyslexia (DD) has been well documented with independent groups reporting a susceptibility locus on chromosome 15q. After the identification of the DYX1C1 gene as a potential candidate for DD, several independent association studies reported controversial results. We performed a family-based association study to determine whether the DYX1C1 single nucleotide polymorphisms (SNPs) that have been associated with DD before, that is SNPs '-3GA' and '1249GT', influence a broader phenotypic definition of DD. A significant linkage disequilibrium was observed with 'Single Letter Backward Span' (SLBS) in both single-marker and haplotype analyses. These results provide further support to the association between DD and DYX1C1 and it suggests that the linkage disequilibrium with DYX1C1 is more saliently explained in Italian dyslexics by short-term memory, as measured by 'SLBS', than by the categorical diagnosis of DD or other related phenotypes.

Wider recognition in peripheral vision common to different subtypes of dyslexia.

Italian children (n = 125) were classified into dyslexics, poor readers and ordinary readers. The dyslexics were further classified into the Boder and Bakker subtypes. The children were tested with the form-resolving field (FRF), which measures central and peripheral visual recognition. Dyslexics show higher correct identification of letters in the periphery, supporting the notion of a different distribution of lateral masking. A numerical characterization of individual FRFs--C2R--reliably distinguishes between dyslexics and ordinary readers. The wider distribution of recognition, similar across the various subtypes of dyslexia, suggests a general characteristic of visual perception, and possibly a different visual-attentional mode.

No evidence for association and linkage disequilibrium between dyslexia and markers of four dopamine-related genes.

Dopamine genes are candidate genes for dyslexia in the light of the well-known comorbidity between dyslexia and ADHD. Within-family association and linkage disequilibrium were tested between four genetic markers at DRD4, DRD3, DRD2, and DAT loci, and dyslexia, in a sample of 130 Italian dyslexic children, 16.9% of whom had comorbid ADHD. No evidence of either association or linkage disequilibrium was found, neither in the total sample nor in the comorbid subgroup. Negative results do not support a common genetic basis between these two disorders for these markers.

Orienting of visual attention in dyslexia: evidence for asymmetric hemispheric control of attention.

The control of attentional orienting was studied in children with specific reading disorder (SRD) or dyslexia, and it was compared with that of normal readers. We used the covert orienting paradigm to measure subjects' reaction times for target detection both in valid and invalid cue conditions, either in the left or in the right visual fields. In experiment 1, we investigated exogenous orienting. The cue consisted of a peripheral abrupt onset and the cue-target delay was 350 ms. As compared with normal readers, in dyslexics the cue effect was absent in the right visual field, whereas in the left visual field a greater cue effect was observed. No visual field asymmetry was found in normal readers. In experiment 2, we investigated endogenous orienting. The cue was shown centrally and the cue-target delay was 750 ms. In dyslexics and normal readers, orienting of attention was present in both visual fields. However, in the invalid condition, dyslexic children showed significantly slower reaction times in the left visual field than in the right visual field. These results were interpreted as being due to an asymmetric control of visual spatial attention, possibly related with a posterior attention mechanism deficit in the right parietal cortex and/or an interhemispheric dysfunction and/or an impairment of cerebellar functions.

Callosal transfer in different subtypes of developmental dyslexia.

Sixteen controls (age 6-13) and 20 native Italian children with developmental dyslexia (age 7-15) received a test of callosal transfer of tactile information. Among the dyslexic children, 7 had a diagnosis of L-type, 7 of P-type and 6 of M-type dyslexia according to Bakker's classification. Both control children and children with dyslexia made a significantly larger number of errors in the crossed localization condition (implying callosal transfer of tactile information) vs. the uncrossed condition. In the same condition, children with dyslexia made a significantly larger number of errors than controls. In the crossed localization condition L-types and M-types made a significantly larger number of errors than P-types and controls, while there was no significant difference in performance between P-types and controls. These findings are discussed in terms of defective callosal transfer or deficient somatosensory representation in children with L- and M-dyslexia.

The spatial distribution of visual attention in developmental dyslexia.

The present study investigated the spatial distribution of visual attention in dyslexic and normally reading children. The performances of the two groups were investigated using two different paradigms. In experiment 1 we analyzed the distribution of processing resources both inside and outside the focus of visual attention by simply recording reaction times to the detection of a white dot target projected at different eccentricities from the fovea. The distribution of attentional resources differed significantly between the two groups of children. The eccentricity of the stimulus was significant only for normally reading children - who showed a normal gradient - as it influenced their detection speed, whereas it had no effect on dyslexic children, who exhibited a diffused distribution of visual processing resources inside the visual field. In experiment 2 we studied the distributed (unfocused) mode of attention in a visual search task by measuring reaction times to a target stimulus inside a large configuration with a variable number of distractors. Results show that as compared to normal children dyslexics are better able to distribute their attentional resources diffusely. Our conclusion is that reading disability may be characterized by a diffused distribution of visual processing resources. These data might be interpreted in the framework of studies on magnocellular deficits in dyslexia, whereby the anomalous distribution of visual attention might explain how transient pathway functioning influences the reading process.