Research on the etiology of dyslexia typically uses an approach based on a single core deficit, failing to understand how variations in combinations of factors contribute to reading development and how this combination relates to intervention outcome. To fill this gap, this study explored links between 28 cognitive, environmental, and demographic variables related to dyslexia by employing a network analysis using a large clinical database of 1,257 elementary school children. We found two highly connected subparts in the network: one comprising reading fluency and accuracy measures, and one comprising intelligence-related measures. Interestingly, phoneme awareness was functionally related to the controlled and accurate processing of letter–speech sound mappings, whereas rapid automatized naming was more functionally related to the automated convergence of visual and speech information. We found evidence for the contribution of a variety of factors to (a)typical reading development, though associated with different aspects of the reading process. As such, our results contradict prevailing claims that dyslexia is caused by a single core deficit. This study shows how the network approach to psychopathology can be used to study complex interactions within the reading network and discusses future directions for more personalized interventions.

The effect of a computerized morpheme-based training procedure on the reading and writing skills of reading-disabled participants (N = 30, mean age = 11.23 years, SD = 0.935) was examined. Considering that fast morphological analysis has been found to have a central role in written word processing of skilled readers, the following training was designed to enhance this process: it consisted of a visual lexical-decision task in which morphologically complex words were visually presented while the duration of the word-stems’ presentation was gradually restricted. A control intervention consisted of the same task, except that the duration of a nonmorphological unit’s presentation was manipulated. The children were divided into two groups: one underwent the morpheme-based intervention, and the other underwent the control intervention. The morpheme-based training procedure had a positive effect beyond that of the control procedure on the spelling of untrained word stems embedded in trained prefixes and suffixes. These results suggest a general improvement in retrieval of orthographic–morphological representations in spelling. Improvements in other measures could, however, not be ascribed to the morphological manipulation alone. These results emphasize the link between morphological processing and spelling. However, the morpheme-based training procedure appears to be less relevant to the improvement of reading.

Parents of 323 twin pairs with reading disability (RD) reported significantly more problems learning to read (16% of mothers and 33% of fathers) than parents of 309 twin pairs without reading difficulties (6% of mothers and 9% of fathers). These rates of self-reported reading problems in parents of twins are highly similar to those previously obtained in parents of non-twin children with RD and controls, suggesting that the etiology of reading deficits in twin and non-twin children may also be highly similar. Moreover, within both the RD and control samples, twins whose parents self-reported a positive history of reading problems had lower reading performance test scores, on average, than those whose parents reported no reading problems. Therefore, results of the present twin study support those of previous studies with non-twin children in which parental self-reports have been found to provide a valid index of family history status for reading difficulties. Twin Research (2000) 3, 88–91.

A number of explanations have been proposed in recent years to account for the observed preponderance of boys with a reading disability. The most notable explanations offered for gender differences in reading disability relate to differences in phonemic awareness, auditory processing, behaviour, neurology, variability in cognitive ability and reading motivation. The purpose of this article was to review the available evidence supporting each of these explanations. The impact of confounding variables, including sample selection, sample bias, intelligence, and socioeconomic status was also discussed. Although the different explanations have, to some degree, an impact on overall reading achievement, it does not appear that any single explanation wholly accounts for gender differences in reading ability, and that gender is not a strong or consistent predictor of reading success.

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 8½ 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.

Male vulnerability to neurodevelopmental disorders remains controversial. For one disorder, reading disability, this sex bias has been interpreted as an artifact of referral bias. We investigated sex differences for the incidence of reading disability within a large prospective sample of White (N = 16,910) and Black (N = 15,313) children derived from the National Collaborative Perinatal Project (NCPP). Children were classified as having either moderate or severe reading disability when they had reading scores lower than 1.5 or 2.0 standard errors of prediction, respectively, given their age and intelligence. Reading disability was about twice as common in boys than girls (p < .001), irrespective of race, severity of disability, or exclusion of children with attentional disturbances or high activity levels. We conclude that there is a clear sex bias toward males for the incidence of reading disabilities. (JINS, 2000, 6, 433–442.)

In order to investigate the possible causal relationships between hyperactivity and educational underachievement that might account for their frequent co-occurrence, four groups of boys, defined by the presence or absence of hyperactivity and specific reading retardation, were identified in an epidemiological study of 7–8-year-old children. They were examined in detail by means of parental interviews and psychological tests and reassessed 9 years later at the age of 16–18 years on a similar range of measures. The findings provided little support for the idea that persistent reading disabilities either lead to the development of hyperactivity de novo or increased the likelihood that hyperactivity, when present, would persist. Similarly, although features of hyperactivity persisted to follow-up, there was little evidence that they either lead to the development of reading disabilities or increased the likelihood that reading disabilities, when present, would persist. Socioeconomic adversity and a history of speech therapy were more common in the group with both hyperactivity and reading disability, but the strength of these associations made it unlikely that these factors could account for the frequent co-occurrence of the two conditions.

Reading and mathematics performance data from a sample of 264 reading-disabled twin pairs and 182 matched control twin pairs were subjected to multivariate behavior genetic analysis. The factor structure of reading and math performance measures was found to be highly similar for both groups. Consistent with previous findings obtained using alternative methods, a significant heritable component to individual differences in reading performance was found both within the reading-disabled (h2 = 0.78) and control (h2 = 0.74) twin samples. In addition, a substantial genetic influence on mathematics performance was found (h2 = 0.51 and 0.60 in the reading-disabled and control samples, respectively), although shared environmental influences common to both members of a twin pair also contribute significantly to the variance in math scores of both groups (c2 = 0.44 and 0.37). Moreover, genetic influences accounted for 98% of the observed correlation between reading and math performance within the sample of reading-disabled twin pairs, and for 55% of the observed correlation in the control sample. Thus, individual differences in both reading and mathematics perfomance are highly heritable and appear to be caused by many of the same genetic influences.

In 1975 the Australian Council of Educational Research (ACER) conducted a nationwide survey of literacy and numeracy in 10- to 14-year olds. A total of 297 of the 12875 children involved were twins. By age 14, only 42% of the twin boys achieved adequate standards of literacy compared with 71% of single-born boys. The deficit in twin girls was much less and twins of both sexes were only moderately behind in numeracy. A survey of 9-13-year-old twin boys in the La Trobe Twin Study (LTS) produced similar results with 75% being below average in reading skills and 23% behind by 18 months or more, despite above average IQs. The ACER data are corroborated by teachers' reports obtained in the same survey, which indicate also how few of the twins with problems are receiving remediation and the high incidence of classroom problems in spelling and reading reversals. The pattern of mistakes twins make on specific items in the ACER survey can be explained as resulting either from specific cognitive deficits or from problems in concentration. The same factors influence performance on different tasks, so that literacy and numeracy are much more closely interrelated in twins than in singletons, and also correlate more with a measure of verbal intelligence. Implications for genetic analysis of scholastic achievement are examined, centering around the different factor structure of abilities in twins and common family environmental effects which are unique to twins.