Visual word form processing deficits driven by severity of reading impairments in children with developmental dyslexia.

The visual word form area (VWFA) in the left ventral occipito-temporal (vOT) cortex is key to fluent reading in children and adults. Diminished VWFA activation during print processing tasks is a common finding in subjects with severe reading problems. Here, we report fMRI data from a multicentre study with 140 children in primary school (7.9-12.2 years; 55 children with dyslexia, 73 typical readers, 12 intermediate readers). All performed a semantic task on visually presented words and a matched control task on symbol strings. With this large group of children, including the entire spectrum from severely impaired to highly fluent readers, we aimed to clarify the association of reading fluency and left vOT activation during visual word processing. The results of this study confirm reduced word-sensitive activation within the left vOT in children with dyslexia. Interestingly, the association of reading skills and left vOT activation was especially strong and spatially extended in children with dyslexia. Thus, deficits in basic visual word form processing increase with the severity of reading disability but seem only weakly associated with fluency within the typical reading range suggesting a linear dependence of reading scores with VFWA activation only in the poorest readers.

A common variant in myosin-18B contributes to mathematical abilities in children with dyslexia and intraparietal sulcus variability in adults.

The ability to perform mathematical tasks is required in everyday life. Although heritability estimates suggest a genetic contribution, no previous study has conclusively identified a genetic risk variant for mathematical performance. Research has shown that the prevalence of mathematical disabilities is increased in children with dyslexia. We therefore correlated genome-wide data of 200 German children with spelling disability, with available quantitative data on mathematic ability. Replication of the top findings in additional dyslexia samples revealed that rs133885 was a genome-wide significant marker for mathematical abilities (P(comb) = 7.71 × 10(-10), n = 699), with an effect size of 4.87%. This association was also found in a sample from the general population (P = 0.048, n = 1080), albeit with a lower effect size. The identified variant encodes an amino-acid substitution in MYO18B, a protein with as yet unknown functions in the brain. As areas of the parietal cortex, in particular the intraparietal sulcus (IPS), are involved in numerical processing in humans, we investigated whether rs133885 was associated with IPS morphology using structural magnetic resonance imaging data from 79 neuropsychiatrically healthy adults. Carriers of the MYO18B risk-genotype displayed a significantly lower depth of the right IPS. This validates the identified association between rs133885 and mathematical disability at the level of a specific intermediate phenotype.

Evidence for the involvement of ZNF804A in cognitive processes of relevance to reading and spelling.

Previous studies have shown that individuals with schizophrenia and dyslexia display common neurocognitive abnormalities. The aim of the present study was to determine whether known schizophrenia-risk genes contribute to dyslexia risk or to disease-relevant cognitive functions. For this purpose, we genotyped the schizophrenia-associated risk variants within zinc-finger protein 804A (ZNF804A), transcription-factor 4 and neurogranin in a large dyslexia case-control sample. We tested all variants for association with dyslexia (927 cases, 1096 controls), and with eight language-relevant cognitive processes (1552 individuals). We observed six significant associations between language-relevant traits and the ZNF804A-variant rs1344706. Interestingly, the ZNF804A schizophrenia risk variant was associated with a better cognitive performance in our data set. This finding might be consistent with a previously reported ZNF804A association in schizophrenia, in which patients carrying the schizophrenia-risk allele at rs1344706 showed a better performance in two memory tests. In conclusion, the present study provides evidence that ZNF804A might have a role in cognitive traits of relevance to reading and spelling, and underlines the phenotypic complexity that might be associated with ZNF804A.

Word recognition deficits in German: more evidence from a representative sample.

In a representative sample of German speaking dyslexic children, earlier findings on dyslexia in the highly consistent orthography of German were confirmed. In a sample of 78 dyslexic 3rd graders selected on the basis of their poor word recognition skills, reading accuracy for both words and non-words was deficient but high in absolute terms. This indicates that the highly consistent grapheme-phoneme correspondences of German orthography in combination with the straightforward phonics teaching approach, which is usually applied in Austrian primary schools, allows even dyslexic children to acquire the process of phonological decoding. The central reading problem was extremely slow speed. Poor performance on a reading comprehension test was at least partly due to slow reading speed as well. Dyslexic children's spelling development was also severely delayed. The number of phonologically incorrect spellings was low; however, dyslexic children quite often produced spellings that are orthographically incorrect, indicating that they have not yet been able to develop an extensive and easily accessible orthographic lexicon. The most prominent cognitive deficit was reduced rapid naming speed closely followed by deficits in phonological awareness. Deficits in phonological memory were also evident (but mild) showing that despite marked differences in findings on reading and spelling skills of English dyslexic children, the underlying causes are very similar. The present sample of dyslexic children showed deficits in visual processing speed in addition to their linguistic deficits. However, this deficit in visual processing speed did not seem causally related to the children's reading and spelling deficits.

The impact of orthographic consistency on dyslexia: a German-English comparison.

We examined reading and phonological processing abilities in English and German dyslexic children, each compared with two control groups matched for reading level (8 years) and age (10-12 years). We hypothesised that the same underlying phonological processing deficit would exist in both language groups, but that there would be differences in the severity of written language impairments, due to differences in orthographic consistency. We also hypothesized that systematic differences due to orthographic consistency should be found equally for normal and dyslexic readers. All cross-language comparisons were based on a set of stimuli matched for meaning, pronunciation and spelling. The results supported both hypotheses: On a task challenging phonological processing skills (spoonerisms) both English and German dyslexics were significantly impaired compared to their age and reading age controls. However, there were extremely large differences in reading performance when English and German dyslexic children were compared. The evidence for systematic differences in reading performance due to differences in orthographic consistency was similar for normal and for dyslexic children, with English showing marked adverse effect on acquisition of reading skills.

The relationship of phonemic awareness to reading acquisition: more consequence than precondition but still important.

Three studies examined the presence of phonemic awareness among Austrian children before reading instruction and its relationship to concurrent and later reading. These children were about 6-7 years of age but in the majority of cases unable to read when they entered school. Testing phonemic awareness with a newly developed, rather simple and natural vowel substitution task revealed that many children showed not a single correct response or little success. In contrast, the few readers at the beginning of grade one exhibited high phonemic awareness and after a few months of reading instruction most of the children scored at least close to perfect in the vowel substitution task. Despite this apparent effect of reading on phonemic awareness there was a specific predictive relationship between initial phonemic awareness differences and success in learning to read and to spell. In agreement with other studies it was found that phonemic awareness differences before instruction predicted the accuracy of alphabetic reading and spelling at the end of grade one independent from IQ and initial differences in letter knowledge and reading. However, closer examination of the relationship between phonemic awareness before instruction and later success in learning to read revealed a specific pattern. Children with high phonemic awareness at the beginning of grade one showed uniformly high reading and spelling achievement at the end of grade one. Such good progress in learning to read and to spell was also evident in the majority of children who showed no phonemic awareness at the beginning of reading instruction, but some of the many children with low phonemic awareness before instruction experienced difficulties in learning to read and to spell. This specific pattern suggests that individual differences in the ease or difficulty with which phonemic awareness can be induced by preschool experiences or by reading instruction is the critical variable underlying the observed correlations between phonemic awareness measures before reading instruction and progress in learning to read.