The DCDC2 deletion is not a risk factor for dyslexia.

Dyslexia is a specific impairment in learning to read and has strong heritability. An intronic deletion within the DCDC2 gene, with ~8% frequency in European populations, is increasingly used as a marker for dyslexia in neuroimaging and behavioral studies. At a mechanistic level, this deletion has been proposed to influence sensory processing capacity, and in particular sensitivity to visual coherent motion. Our re-assessment of the literature, however, did not reveal strong support for a role of this specific deletion in dyslexia. We also analyzed data from five distinct cohorts, enriched for individuals with dyslexia, and did not identify any signal indicative of associations for the DCDC2 deletion with reading-related measures, including in a combined sample analysis (N=526). We believe we conducted the first replication analysis for a proposed deletion effect on visual motion perception and found no association (N=445 siblings). We also report that the DCDC2 deletion has a frequency of 37.6% in a cohort representative of the general population recruited in Hong Kong (N=220). This figure, together with a lack of association between the deletion and reading abilities in this cohort, indicates the low likelihood of a direct deletion effect on reading skills. Therefore, on the basis of multiple strands of evidence, we conclude that the DCDC2 deletion is not a strong risk factor for dyslexia. Our analyses and literature re-evaluation are important for interpreting current developments within multidisciplinary studies of dyslexia and, more generally, contribute to current discussions about the importance of reproducibility in science.

Lack of replication for the myosin-18B association with mathematical ability in independent cohorts.

Twin studies indicate that dyscalculia (or mathematical disability) is caused partly by a genetic component, which is yet to be understood at the molecular level. Recently, a coding variant (rs133885) in the myosin-18B gene was shown to be associated with mathematical abilities with a specific effect among children with dyslexia. This association represents one of the most significant genetic associations reported to date for mathematical abilities and the only one reaching genome-wide statistical significance. We conducted a replication study in different cohorts to assess the effect of rs133885 maths-related measures. The study was conducted primarily using the Avon Longitudinal Study of Parents and Children (ALSPAC), (N = 3819). We tested additional cohorts including the York Cohort, the Specific Language Impairment Consortium (SLIC) cohort and the Raine Cohort, and stratified them for a definition of dyslexia whenever possible. We did not observe any associations between rs133885 in myosin-18B and mathematical abilities among individuals with dyslexia or in the general population. Our results suggest that the myosin-18B variant is unlikely to be a main factor contributing to mathematical abilities.

Accessing and selecting word meaning in autism spectrum disorder.

BACKGROUND: Comprehension difficulties are commonly reported in autism spectrum disorder (ASD) but the causes of these difficulties are poorly understood. This study investigates how children with ASD access and select meanings of ambiguous words to test four hypotheses regarding the nature of their comprehension difficulties: semantic deficit, weak central coherence, reduced top-down control and inhibition deficit. METHODS: The cross-modal semantic priming paradigm was used. Children heard homonym primes in isolation or as final words in sentences biased towards the subordinate meaning and then named picture targets depicting dominant or subordinate associates of homonyms. RESULTS: When homonyms were presented in isolation, children with ASD and controls showed priming for dominant and subordinate pictures at 250ms ISI. At 1,000ms ISI, the controls showed dominant (but not subordinate) priming whilst the ASD group did not show any priming. When homonyms were presented in subordinate sentence contexts, both groups only showed priming for context-appropriate (subordinate) meanings at 250ms ISI, suggesting that context has an early influence on meaning selection. At 1,000ms ISI the controls showed context-appropriate (but not inappropriate) priming whereas the ASD group showed both appropriate and inappropriate priming. CONCLUSIONS: Children with ASD showed intact access to semantic information early in the time course of processing; however, they showed impairments in the selection of semantic representations later in processing. These findings suggest that a difficulty with initiating top-down strategies to modulate online semantic processing may compromise language comprehension in ASD. Implications for intervention are discussed.

Persistence of literacy problems: spelling in adolescence and at mid-life.

BACKGROUND: Developmental reading problems show strong persistence across the school years; less is known about poor readers' later progress in literacy skills. METHOD: Poor (n = 42) and normally developing readers (n = 86) tested in adolescence (ages 14/15 years) in the Isle of Wight epidemiological studies were re-contacted at mid-life (ages 44/45 years). Participants completed a spelling test, and reported on educational qualifications, perceived adult spelling competence, and problems in day-to-day literacy tasks. RESULTS: Individual differences in spelling were highly persistent across this 30-year follow-up, with correlations between spelling at ages 14 and 44 years of r = .91 (p < .001) for poor readers and r = .89 (p < .001) for normally developing readers. Poor readers' spelling remained markedly impaired at mid-life, with some evidence that they had fallen further behind over the follow-up period. Taking account of adolescent spelling levels, continued exposure to reading and literacy demands in adolescence and early adulthood was independently predictive of adult spelling in both samples; family social background added further to prediction among normally developing readers only. CONCLUSIONS: By adolescence, individual differences in spelling and its related sub-skills are highly stable. Encouraging young people with reading disabilities to maintain their exposure to reading and writing may be advantageous in the longer term.

The relationship between paired associate learning and phonological skills in normally developing readers.

Seventy-five 6- to 11-year-old children were administered tests of phonological awareness, verbal short term memory (STM), and visual-verbal paired associate learning (PA learning) to investigate their relationship with word recognition and decoding skills. Phonological awareness was a stronger concurrent predictor of word recognition than verbal STM, and phonological awareness but not verbal STM was a predictor of learning in the PA learning task. Importantly, measures of phonological awareness and PA learning both accounted for independent variance in word reading, even when decoding skill was controlled. The results suggest that PA learning and phonological awareness tasks tap two separate mechanisms involved in learning to read. The results are discussed in relation to current theories of reading development.

Rapid auditory processing and phonological ability in normal readers and readers with dyslexia.

According to a prominent theory, the phonological difficulties in dyslexia are caused by an underlying general impairment in the ability to process sequences of rapidly presented, brief sounds. Two studies examined this theory by exploring the relationships between rapid auditory processing and phonological processing in a sample of 82 normally reading children (Study 1) and by comparing 17 children with dyslexia to chronological-age and reading-age control participants on these tasks (Study 2). In the normal readers, moderate correlations were found between the measure of rapid auditory processing (Auditory Repetition Task, or ART) and phonological ability. On the ART, the dyslexia group performed at a level similar to that of the reading-age control group but obtained scores that were significantly below those of the chronological-age control group. This difference was due to a subgroup of 4 children in the dyslexia group who had particular difficulty with the ART. The phonological skills of these individuals were not worse than those of the children in the dyslexia group who were unimpaired on the ART. The discussion argues that there is no evidence that phonoogical difficulties are secondary to impairments of rapid auditory processing, as measured by the ART, and highlights the need to examine the strategic and cognitive demands involved in tasks of rapid auditory processing.

Educational attainments of school leavers with a preschool history of speech-language impairments.

This paper reports a follow-up study of a cohort of 16- and 17-year-olds with a preschool history of speech-language impairment and whom Bishop and Edmundson (1987) originally studied. Information collected by questionnaire showed that the GCSE grades of those whose language impairments had resolved by 5;06 were below those of age-matched controls. However, the number of GCSE examinations entered and passed was significantly more than those of the 'persistent S-LI' and 'general delay' groups. Overall, IQ was the strongest predictor of educational attainment. However, even when IQ was controlled, literacy skills accounted for independent variance in achievement, especially among those with a history of language difficulty. The survey also noted that the majority of students across all groups remained in full-time education; however, the adolescents with a background of S-LI were more likely to follow vocational and employment training courses rather than A-levels.

From language to reading and dyslexia.

This paper reviews evidence in support of the phonological deficit hypothesis of dyslexia. Findings from two experimental studies suggest that the phonological deficits of dyslexic children and adults cannot be explained in terms of impairments in low-level auditory mechanisms, but reflect higher-level language weaknesses. A study of individual differences in the pattern of reading skills in dyslexic children rejects the notion of 'sub-types'. Instead, the findings suggest that the variation seen in reading processes can be accounted for by differences in the severity of individual children's phonological deficits, modified by compensatory factors including visual memory, perceptual speed and print exposure. Children at genetic risk who go on to be dyslexic come to the task of reading with poorly specified phonological representations in the context of a more general delay in oral language development. Their prognosis (and that of their unaffected siblings) depends upon the balance of strengths and difficulties they show, with better language skills being a protective factor. Taken together, these findings suggest that current challenges to the phonological deficit theory can be met.

Is preschool language impairment a risk factor for dyslexia in adolescence?

The literacy skills of 56 school leavers from the Bishop and Edmundson (1987) cohort of preschoolers with specific language impairment (SLI) were assessed at 15 years. The SLI group performed worse on tests of reading, spelling, and reading comprehension than age-matched controls and the literacy outcomes were particularly poor for those with Performance IQ less than 100. The rate of specific reading retardation in the SLI group had increased between the ages of 8 1/2 and 15 years and there had been a substantial drop in reading accuracy, relative to age. However, over 35% had reading skills within the normal range and those who had had isolated impairments of expressive phonology had a particularly good outcome. Our findings highlight the limitations of discrepancy definitions of dyslexia that do not take account of the changing demands of reading over time. We argue that children's phonological difficulties place them at risk of literacy failure at the outset of reading and that later, impairments of other language skills compromise development to adult levels of fluency.

Precursors of literacy delay among children at genetic risk of dyslexia.

This paper reports the literacy skills of 63 children selected as being at genetic risk of dyslexia compared with 34 children from families reporting no history of reading impairment. Fifty-seven per cent of the at-risk group were delayed in literacy development at 6 years compared with only 12% of controls. The "unimpaired" at-risk group were not statistically different from controls on most cognitive and language measures at 45 months, whereas the literacy-delayed group showed significantly slower speech and language development, although they did not differ from controls in nonverbal ability. Letter knowledge at 45 months was the strongest predictor of literacy level at 6 years. In addition, early speech and language skills predicted individual differences in literacy outcome and genetic risk accounted for unique variance over and above these other factors. The results are discussed in terms of an interactive developmental model in which semantic and phonological skills support early reading acquisition.

Is dyslexia a form of specific language impairment? A comparison of dyslexic and language impaired children as adolescents.

Two groups of adolescents with a childhood history of language impairment were compared with a group of developmentally dyslexic young people of the same age and nonverbal ability. The study also included two comparison groups of typically developing children, one of the same age as those in the clinical groups, and a younger comparison group of similar reading level to the dyslexic students. Tests of spoken and written language skills revealed that the adolescents with dyslexia were indistinguishable from those with resolved language impairments on spoken language tasks, and both groups performed at age-expected levels. However, both dyslexic readers and those with resolved specific language impairments showed deficits in phonological awareness. On written language tasks, a different pattern of performance was apparent. In reading and spelling, adolescents with dyslexia performed only as well as those with persistent oral language impairments and younger controls. However, their reading comprehension was better. The theoretical and educational implications of these findings are discussed.

Working memory deficits in poor comprehenders reflect underlying language impairments.

Three experiments assessed memory skills in good and poor comprehenders, matched for decoding skill. Experiments 1 and 2 investigated phonological and semantic contributions to short-term memory by comparing serial recall for words varying in length, lexicality, and concreteness. Poor comprehenders showed normal sensitivity to phonological manipulations (length and lexicality) but, consistent with their semantic weaknesses, their recall of abstract words was poor. Experiment 3 investigated verbal and spatial working memory. While poor comprehenders achieved normal spatial spans, their verbal spans were impaired. These results are discussed within a theoretical framework in which the memory difficulties associated with poor reading comprehension are specific to the verbal domain and are a concomitant of language impairment, rather than a cause of reading comprehension failure.

Developmental differences in sensitivity to semantic relations among good and poor comprehenders: evidence from semantic priming.

Semantic priming for category coordinates (e.g. CAT-DOG; AEROPLANE-TRAIN) and for pairs of words related through function (e.g. BROOM-FLOOR; SHAMPOO-HAIR) was assessed in children with good and poor reading comprehension, matched for decoding skill. Lexical association strength was also manipulated by comparing pairs of words that were highly associated with pairs that shared low association strength. Both groups of children showed priming for function-related words, but for the category co-ordinates, poor comprehenders only showed priming if the category pairs also shared high association strength. Good comprehenders showed priming for category-related targets, irrespective of the degree of prime-target association. These findings are related to models of language development in which category knowledge is gradually abstracted and refined from children's event-based knowledge and it is concluded that in the absence of explicit co-occurrence, poor comprehenders are less sensitive to abstract semantic relations than normal readers.

Problems of behaviour, reading and arithmetic: assessments of comorbidity using the Strengths and Difficulties Questionnaire.

BACKGROUND: Estimates of academic underachievement among school children vary widely, depending on the geographical location and on the criteria used to define attainment. AIM: To examine the relationship between behaviour problems and academic attainment in a large UK primary school. METHOD: A school population (364 children from Years 3 to 6 inclusive) were assessed on a range of cognitive ability tasks. These included standardised tests of reading, arithmetic and verbal and non-verbal intelligence. Under-achievement was assessed using different criteria. To assess behaviour, teachers completed the Strengths and Difficulties Questionnaire (Goodman, 1997) for each participating child. Finally, academic progress of a subset of children was assessed after one year. RESULTS: Indicated a significant relationship between behaviour and academic attainment; prosocial behaviour was positively correlated with reading and arithmetic, hyperactivity and conduct problems were negatively correlated. This association was especially strong in the children rated by the questionnaire as hyperactive, where around 1 in 5 had a specific reading deficit. However, there was no evidence to indicate that children with behaviour problems made less academic progress over a one-year period relative to their peers. CONCLUSION: The study highlights the importance of assessing both cognitive skills and behaviour, particularly when planning the educational management of children with reading difficulties.

Individual differences in contextual facilitation: evidence from dyslexia and poor reading comprehension.

Ninety-two 7- to 10-year-old children read words presented in isolation or following a spoken sentence context. In absolute terms, poor readers showed more contextual facilitation than good readers. However, when the relative benefit of context was assessed, this was greater for children with better reading skills, and comprehension was a better predictor of contextual facilitation than decoding. Study 2 compared the performance of dyslexics with that of reading-age matched poor comprehenders and normal readers. The dyslexics showed greater contextual facilitation than the normal readers who, in turn, showed more priming than poor comprehenders. The results show that dyslexic children use context to compensate for poor decoding skills, whereas children with poor reading comprehension skills fail to benefit from context as much as normal readers.

Segmentation, not rhyming, predicts early progress in learning to read.

We present a longitudinal study of children in the first 2 years of learning to read. A battery of tests of phonological skills administered when the children were prereaders identified two distinct and relatively independent factors, Rhyming (defined by measures of rhyme detection and rhyme production) and Segmentation (defined by measures of phoneme identification and phoneme deletion). Segmentation was strongly correlated with attainment in reading and spelling at the end of the first year at school, while Rhyming was not. In addition, letter name knowledge predicted both reading and spelling skill and showed an interactive effect with children's segmentation skills. By the end of the second year of school, however, rhyming had started to exert a predictive effect on spelling, but not on reading. The results are discussed in the context of current theories of the role of phonological skills in learning to read.

Segmentation does predict early progress in learning to read better than rhyme: A reply to bryant

In our recent paper (Muter, Hulme, Snowling, & Taylor, 1997) we argued that measures of segmentation were better predictors of early progress in learning to read than were measures of rhyme. Bryant (1998, this issue), in his comment on our paper, has argued that this conclusion is flawed because the instructions used in our rhyme detection measure included the phrase "rhymes with or sounds like." We present new data showing that the instructions used do not have the effect Bryant claims: asking children which word "rhymes with" or which word "rhymes with or sounds like" a target word produces identical patterns of responses. We argue that Bryant's new measure derived from our data simply reflects children's global sensitivity to the similarity in sound between different words and that this measure provides no convincing support for his conclusion that sensitivity to onset and rime is a predictor of children's success in learning to read. We conclude that the data in our paper, as well as other recent evidence, support the view that measures of phonemic segmentation are better predictors of early reading skills than are measures of onset-rime sensitivity. Copyright 1998 Academic Press.

Language-impaired preschoolers: a follow-up into adolescence.

This paper reports a longitudinal follow-up of 71 adolescents with a preschool history of speech-language impairment, originally studied by Bishop and Edmundson (1987). These children had been subdivided at 4 years into those with nonverbal IQ 2 SD below the mean (General Delay group), and those with normal nonverbal intelligence (SLI group). At age 5;6 the SLI group was subdivided into those whose language problems had resolved, and those with persistent SLI. The General Delay group was also followed up. At age 15-16 years, these children were compared with age-matched normal-language controls on a battery of tests of spoken language and literacy skills. Children whose language problems had resolved did not differ from controls on tests of vocabulary and language comprehension skills. However, they performed significantly less well on tests of phonological processing and literacy skill. Children who still had significant language difficulties at 5;6 had significant impairments in all aspects of spoken and written language functioning, as did children classified as having a general delay. These children fell further and further behind their peer group in vocabulary growth over time.

Assessing reading difficulties: the validity and utility of current measures of reading skill.

BACKGROUND: Accurate assessment of reading difficulties is clearly important if appropriate support and remediation is to be provided. Many different reading tests are routinely used yet it is not clear to what extent different tests tap the same underlying skills. AIMS: The nature of the relationships between different tests of reading accuracy, reading comprehension and linguistic comprehension is investigated in this paper. SAMPLES, METHODS AND RESULTS: In study 1, 184 7-10 year old children completed a listening comprehension test, three tests of reading accuracy (reading of nonwords, single words and text) and two tests of reading comprehension (test comprehension and sentence completion). While sentence completion was well accounted for by individual differences in word recognition, text comprehension was more heavily dependent on listening comprehension. Study 2 compared the performance of children with poor comprehension skills with controls matched for age, nonverbal ability and decoding skill. The poor comprehenders had greatest difficulty with those tests most heavily dependent on linguistic comprehension and least difficulty on purer measures of decoding. CONCLUSIONS: These findings show that different reading tests measure different aspects of the reading process and that caution should be exercised when selecting tests for the assessment of reading difficulties.