Genes, environment, and dyslexia the 2005 Norman Geschwind memorial lecture

This article presents an overview of some methods and results from our continuing studies of genetic and environmental influences on dyslexia, and on individual differences across the normal range that have been conducted over the past 25 years in the Colorado Learning Disabilities Research Center (CLDRC) and in related projects. CLDRC investigators compare the similarities of identical twin pairs who share all their genes and fraternal twins who share half their segregating genes to assess the balance of genetic, shared family environment, and nonshared environment influences on dyslexia and on individual differences across the normal range. We have learned that among the children we have studied in Colorado, group deficits in reading (dyslexia) and individual differences in reading across the normal range are primarily due to genetic influences, and these genetic influences are often shared with some of the same genetic influences on deficits and individual differences in language and ADHD. We have also learned from our molecular-genetic linkage studies that there are regions on several chromosomes likely to contain genes that influence dyslexia. Several specific genes within these regions have been tentatively identified through molecular-genetic association analyses, but much more research is needed to understand the pathways among specific genes, regions of noncoding DNA that regulate the activity of those genes, the brain, and dyslexia. I conclude with a discussion of our research on individual differences in early reading development, on the role of early learning constraints in dyslexia, and on how genetic influences are expressed through their interaction and correlation with the environment.     

Reading disability and chromosome 6p21.3: evaluation of MOG as a candidate gene

Linkage analysis has localized a gene influencing specific reading disability (dyslexia) to 6p21.3. The myelin oligodendrocyte glycoprotein (MOG) gene, which maps to this region, was selected as a candidate. Myelin oligodendrocyte glycoprotein is a membrane protein, a member of the immunoglobin superfamily, that is found on the outermost lamellae of mature myelin. Although the exact function of this protein is unknown, its presence in the central nervous system and the hypothesized relationship between dyslexia and temporal processing rate as well as a suggested relationship with intelligence made this gene a candidate for dyslexia. Analysis of the coding exons and adjacent splice sites in a subset of 22 children with dyslexia from 10 sibships found a missense mutation in exon 4 in 2 of the sibships. This change from the published sequence also occurred in 86 of 96 random controls, making it considerably less frequent in this small sample of individuals with dyslexia. Subsequent typing of this single nucleotide polymorphism (SNP) in 74 nuclear families in which at least one child had reading disability showed no significant difference in frequency from the controls, however. Sib-pair linkage analysis with these families did not show significant linkage with the SNP nor with a separate polymorphic dinucleotide repeat marker in the MOG gene (MOG31/32), but association analysis identified two alleles of MOG31/32 that were associated with reading disability phenotypes with a low level of significance. Thus, although alleles in the MOG gene may be in linkage disequilibrium with a locus that contributes to reading disability, it is unlikely that the MOG gene itself is involved.     

Developmental dyslexia: Related to specific or general deficits?

The present study was designed to examine the question of whether developmental dyslexia in 12-year-old students at the beginning of secondary education in the Netherlands is confined to problems in the domain of reading and spelling or also is related to difficulties in other areas. In particular, hypotheses derived from theories on phonological processing, rapid automatized naming, working memory, and automatization of skills were tested. To overcome the definition and selection problems of many previous studies, we included in our study all students in the first year of secondary special education in a Dutch school district. Participants were classified as either dyslexic, garden-variety, or hyperlexic poor readers, according to the degree of discrepancy between their word recognition and listening comprehension scores. In addition, groups of normal readers were formed, matching the poor readers in either reading age or chronological age. A large test battery was administered to each student, including phonological, naming, working memory, speed of processing, and motor tests. The findings indicate that dyslexia is associated with deficits in (1) phonological recoding, word recognition (both in their native Dutch and in English as a second language), and spelling skills; and (2) naming speed for letters and digits. Dyslexia was not associated with deficits in other areas. The results suggest that developmental dyslexia, at the age of 12, might be (or might have become) a difficulty rather isolated from deficiencies in other cognitive and motor skills.     

Atypical predictive processing during visual statistical learning in children with developmental dyslexia: an event-related potential study

Previous research suggests that individuals with developmental dyslexia perform below typical readers on non-linguistic cognitive tasks involving the learning and encoding of statistical-sequential patterns. However, the neural mechanisms underlying such a deficit have not been well examined. The aim of the present study was to investigate the event-related potential (ERP) correlates of sequence processing in a sample of children diagnosed with dyslexia using a non-linguistic visual statistical learning paradigm. Whereas the response time data suggested that both typical and atypical readers learned the statistical patterns embedded in the task, the ERP data suggested otherwise. Specifically, ERPs of the typically developing children (n?=?12) showed a P300-like response indicative of learning, whereas the children diagnosed with a reading disorder (n?=?8) showed no such ERP effects. These results may be due to intact implicit motor learning in the children with dyslexia but delayed attention-dependent predictive processing. These findings are consistent with other evidence suggesting that differences in statistical learning ability might underlie some of the reading deficits observed in developmental dyslexia.     

Developmental dyslexia: Heterogeneity without discrete subgroups

Is the dual route model of word recognition useful in explaining individual differences in reading behaviors for most developmental dyslexics? Many past case studies of surface and phonological acquired dyslexics and a few similar studies of developmental dyslexia have suggested this might be so. The present study investigated individual differences among a group of 65 dyslexics, age 10 to 13, in reading, phonemic segmentation, and word retrieval. The dyslexics’ performance was compared to that of 65 reading age controls and 17 age-matched good readers. The research questions were: (1) Are there discrete subgroups of developmental dyslexics as suggested by the case studies? (2) How do oral language measures relate to the various reading tasks? The data indicated there were no discrete subgroups within the group of dyslexics; in addition, the variability in performance on reading tasks was quite similar for the dyslexic and reading age-control groups. A few dyslexics resembled phonological dyslexics and surface dyslexics, but these subjects were still part of a continuum. We also report the relationship between phonemic segmentation and word retrieval and various reading tasks. It appears that dyslexics at extreme ends of the continuum may exhibit quite different patterns from each other in their oral language task performance as well as in their reading.     

Phonological and visual processing deficits can dissociate in developmental dyslexia: Evidence from two case studies

The present study describes two Frenchteenagers with developmental reading andwriting impairments whose performance wascompared to that of chronological age andreading age matched non-dyslexic participants.Laurent conforms to the pattern of phonologicaldyslexia: he exhibits a poor performance inpseudo-word reading and spelling, producesphonologically inaccurate misspellings butreads most exception words accurately. Nicolas,in contrast, is poor in reading and spelling ofexception words but is quite good atpseudo-word spelling, suggesting that hesuffers from surface dyslexia and dysgraphia.The two participants were submitted to anextensive battery of metaphonological tasks andto two visual attentional tasks. Laurentdemonstrated poor phonemic awareness skills butgood visual processing abilities, while Nicolasshowed the reverse pattern with severedifficulties in the visual attentional tasksbut good phonemic awareness. The presentresults suggest that a visual attentionaldisorder might be found to be associated withthe pattern of developmental surface dyslexia.The present findings further show thatphonological and visual processing deficits candissociate in developmental dyslexia.     

Norman geschwind lecture: Geschwind’s lesson

Norman Geschwind had a profound effect on behavioral neurology, not only on the basis of his research and theories expressed during his lifetime, but also through the impact that he had on colleagues privileged to train under him or have their work personally influenced by him. My work falls into the latter category. Novel associations between brain function/structure and behavior characterized his professional contributions, and offer a model for those who follow in his footsteps. He correctly predicted that like aphasic disorders, developmental dyslexia might be associated with deficits in color naming expressed currently as deficits in Rapid Automatized Naming. He stimulated anatomic research regarding patterns of asymmetry and microscopic architecture leading to the establishment of the Orton Dyslexia Neuropathology Laboratory at Beth Israel Hospital, Boston. He predicted an association between autoimmune disorders and reading disorders, an association that proved to be of genetic origin. He further predicted that reading disorders, like language disorders, would be cross-cultural and, similarly, their mechanism of production would be cross-cultural, although affected perhaps by the structure of the language to be learned. His suspicion that the clinical impression of male gender preponderance in dyslexia was accurate and carried biologic significance has recently been reconfirmed by colleagues at the Mayo Clinic in Rochester, Minnesota. Finally, with respect to dyslexia, one should not be surprised that since affect is influenced by brain architecture, developmental disorders characterized by altered brain architecture might be associated with affective or other psychiatric phenomena. My own work suggests that the altered neuroanatomy in dyslexia may be accompanied by altered clinical neurophysiology, offering the possibility that in some developmental disorders, behaviors, including academic aptitude and cognitive function, might benefit from medications designed originally to lower the risk of clinical seizures. Perhaps Geschwind’s greatest lesson is to not assume that all we have been taught as dogma is truth. Rather, we must have a willingness to make clear perceptions and draw conclusions that come closer to the reality of the causal relationship between brain and behavior.     

发展性阅读障碍眼动研究的进展

发展性阅读障碍一直是心理学家关注的重要领域。国外研究者基于认知和生物因素提出了关于发展性阅读障碍的语音缺陷、小脑缺陷、一般性大细胞功能障碍等理论,并考察了患者的眼动特征,提出了有效的诊治方法。汉语发展性阅读障碍研究主要局限在语音和正字法领域,也涉及局部脑区的功能缺陷,但还未从多角度测查其成因,如眼动。该文在理论梳理的基础上,系统探讨了发展性阅读障碍患者的眼动特征及机制。     

Identification of children at risk of dyslexia: the validity of teacher judgements using ‘Phonic Phases’

We report an investigation of the validity of teachers' ratings of children's progress in ‘phonics’ as a screener for dyslexia. Seventy‐three 6‐year‐olds from a whole school population were identified as ‘at risk’ of dyslexia according to teacher judgements of slow progression through phonic phases. Six months later, children's attainments in literacy and phonological skills were compared with those of their typically developing peers matched on age and gender. Teacher assessments of risk were related to individual differences in performance on a standardised test of reading ability. Teacher assessments overestimated ‘risk of dyslexia’, defined as below‐average reading performance. However, teacher judgements, supplemented by tests of phoneme awareness and rapid naming, allowed a sensitive and specific identification of children who subsequently experienced reading difficulties. These findings show teachers can identify risk of dyslexia; the accuracy of this process can be improved by administering two tests of phonological skills.     

Is there a visual dyslexia

Traditionally, it has been speculated that weaknesses in the visual processing of cognitive aspects of the written word could lead to reading problems, and if so, such a condition would constitute a subtype of developmental dyslexia. This putative subtype has been referred to as visual dyslexia. In this article, the role of cognitive deficits that are visual in nature as a potential etiological factor of developmental dyslexia is examined. Following a brief history of the study of dyslexia, a critique of studies of visual dyslexia is presented. Subsequently, the nature of the visual processes involved in word- recognition is examined. Finally, three research studies that assessed the contribution of visual memory to word-recognition are presented. It is concluded that, even though defects in the physiological aspects of visual processing can lead to reading difficulties, at present little convincing evidence is available to conclude that a subtype of dyslexia caused by cognitive deficits associated with visual processing of information exists.     

Investigating the double-deficit hypothesis of developmental dyslexia in an orthography of intermediate depth

The present study aimed to investigate the double-deficit hypothesis (DDH) in an orthography of intermediate depth. Eighty-five European Portuguese-speaking children with developmental dyslexia, aged 7 to 12, were tested on measures of phonological awareness (PA), naming speed (NS), reading, and spelling. The results indicated that PA and NS were not significantly correlated, and that NS predicts reading fluency (but not reading accuracy and spelling) beyond what is accounted for by PA. Although the majority of the children with developmental dyslexia have double deficit (62.4%), some children have a single phonological deficit (24.7%) or a single NS deficit (8.2%). Children with a double deficit were not more impaired in reading fluency, reading accuracy, and spelling than both single-deficit subtypes. In conclusion, the findings of the present study are partially consistent with the DDH and provide evidence for the multifactorial model of developmental dyslexia. Implications of the DDH for an orthography of intermediate depth are emphasized.

     

Evidence-based diagnosis and treatment for specific learning disabilities involving impairments in written and/or oral language

Programmatic, multidisciplinary research provided converging brain, genetic, and developmental support for evidence-based diagnoses of three specific learning disabilities based on hallmark phenotypes (behavioral expression of underlying genotypes) with treatment relevance: dysgraphia (impaired legible automatic letter writing, orthographic coding, and finger sequencing), dyslexia (impaired pseudoword reading, spelling, phonological and orthographic coding, rapid automatic naming, and executive functions; inhibition and rapid automatic switching), and oral and written language learning disability (same impairments as dyslexia plus morphological and syntactic coding and comprehension). Two case studies illustrate how these differential diagnoses can be made within a conceptual framework of a working memory architecture and generate treatment plans that transformed treatment nonresponders into treatment responders. Findings are discussed in reference to the importance of (a) considering individual differences (diagnosis of impaired hallmark phenotypes) in planning and evaluating response to instruction and modifying instruction when a student is not responding; (b) recognizing that teaching may change epigenetic gene expression at one stage of schooling, but not the underlying gene sequences that render individuals still vulnerable as curriculum requirements increase in nature, complexity, and volume in the upper grades; and (c) using evidence-based diagnoses of specific learning disabilities that are consistent across states for free and appropriate education K to 12 and for accommodations throughout higher education and professional credentialing.     

Orthographic processing efficiency in developmental dyslexia: an investigation of age and treatment factors at the sublexical level

Reading fluency beyond decoding is a limitation to many children with developmental reading disorders. In the interest of remediating dysfluency, contributing factors need to be explored and understood in a developmental framework. The focus of this study is orthographic processing in developmental dyslexia, and how it may contribute to reading fluency. We investigated orthographic processing speed and accuracy by children identified with dyslexia that were enrolled in an intensive, fluency-based intervention using a timed visual search task as a tool to measure orthographic recognition. Results indicate both age and treatment effects, and delineate a link between rapid letter naming and efficient orthographic recognition. Orthographic efficiency was related to reading speed for passages, but not spelling performance. The role of orthographic learning in reading fluency and remediation is discussed.     

Coherent motion sensitivity and reading development in the transition from prereading to reading stage

Evidence suggests that sensitivity to coherent motion (CM) is related to reading, but its role in the etiology of developmental dyslexia remains unclear. In this longitudinal study, CM sensitivity was measured in 31 children at family risk for dyslexia and 31 low-risk controls. Children, diagnosed with dyslexia in third grade (mean age=8 years 3 months), demonstrated reduced CM sensitivity in kindergarten (mean age=5 years 8 months), before they had learned to read. Preschool CM thresholds in controls also uniquely predicted future literacy achievement. When reassessed in first grade, CM sensitivity in the dyslexic children was age appropriate, and CM thresholds in the controls no longer predicted literacy acquisition. These findings contribute to the debate about the developmental relations between visual processing and reading acquisition.     

Reading Difficulty Characteristics in Dyslexic and Hearing-impaired Students

This study examines reading difficulty characteristics in Hebrew in three reading-impaired populations. Two are groups of dyslexics: 100 readers with impaired auditory perception and 100 readers with impaired visual perception. The third group comprises 61 readers with deep/severe hearing impairment. All were elementary schools students in the second to sixth grades. The subjects were tested with a conventional Hebrew reading test. It examined types of reading errors (e.g. changes of phonetic structure or word content), self-correction in reading, reading speed, sequential/holistic reading, the effect of reading texts with and without the Hebrew diacritical vowel signs ('punctuation'), and the effect of meaningful or meaningless text material on the amount of reading errors. The literature describes distinctions between various kinds of reading disability related to auditory impairment and visual perception, and the definition of dyslexia as being one category or including sub-groups. Our research hypothesis was that similar characteristics of reading difficulties would be found amongst auditory perception-impaired students and hearing-impaired students, and that they would differ from those of students with impaired visual perception. Our findings support this hypothesis. Many of the sub-tests revealed similarity in the reading difficulties between the hearing impaired students and those with impaired auditory perception versus the visually impaired. An unexpected finding revealed that fourth grade students in all the groups were a special sub-group in each group. These findings suggest, in accordance with a major research approach, that dyslexia should be defined in terms of dyslexia sub-groups rather than as a single category.     

Auditory Processing of Amplitude Envelope Rise Time in Adults Diagnosed With Developmental Dyslexia

Studies of basic (nonspeech) auditory processing in adults thought to have developmental dyslexia have yielded a variety of data. Yet there has been little consensus regarding the explanatory value of auditory processing in accounting for reading difficulties. Recently, however, a number of studies of basic auditory processing in children with developmental dyslexia have suggested that a reduced ability to discriminate the rate of change in amplitude envelope onsets (rise time) may be linked to phonological processing difficulties and thereby to reading difficulties. Here, we select a range of different rise-time tasks used with children, and give them to adults with developmental dyslexia, along with 2 other auditory tasks (intensity discrimination and temporal order judgment). Deficits in both rise-time perception and temporal order judgment were found to predict literacy attainment in adults with developmental dyslexia, but the data were suggestive of different causal pathways.     

发展性阅读障碍的神经机制及其对第二语言学习的影响

研究表明拼音文字系统的发展性阅读障碍者与以中文为代表的表意文字系统的发展性阅读障碍者在阅读过程中大脑的激活部位存在差异。关于母语阅读障碍儿童对第二语言学习的影响是近年来发展性阅读障碍研究的热点。双语发展性阅读障碍的理论假设主要有两种语言相互依赖假设和正字法依赖假设。前者认为母语的阅读障碍可以自动迁移到第二语言的学习中;后者认为母语的阅读障碍是否会迁移到第二语言的学习中,要依赖两种语言的正字法特征。我们认为这两种理论不是相互矛盾的,阅读障碍是否会同时出现在两种语言中可能取决于这两种语言是否共用了相同的有缺陷的神经系统。     

Evaluating the teaching and learning experience for the child with dyslexia in special and mainstream settings in Ireland

This study examines and evaluates special provision for pupils with dyslexia in three different settings: reading schools, reading units and mainstream support. The research focused on the teaching and learning context for pupils with dyslexia, the support teacher, the mainstream teacher and the experience of the student. The main participants were teachers and tutors supporting pupils with dyslexia, and the parents of these children. Survey methods included questionnaires, focus group discussions, interviews and quantitative data on pupils' reading attainment. In addition, a total of six schools, two representing each model of support, were selected as case studies. This article reports part of a larger survey, which evaluated the effectiveness of three models of special provision for children with dyslexia in primary school. The study shows that there are academic and social benefits for the child with dyslexia who is enrolled in a special setting. However, placement in a reading school or reading unit per se does not guarantee that a child will ‘catch up’ with his or her peers. The findings reported a similarity in the methods and practices teachers use in both mainstream and special settings. The discussion suggests that if teachers are to ‘catch them before they fall’ there are serious questions that must be asked about how we are teaching basic literacy skills. The findings suggest an urgent need for a more balanced approach to teaching reading and writing.     

Amplitude envelope perception, phonology and prosodic sensitivity in children with developmental dyslexia

Here we explore relations between auditory perception of amplitude envelope structure, prosodic sensitivity, and phonological awareness in a sample of 56 typically-developing children and children with developmental dyslexia. We examine whether rise time sensitivity is linked to prosodic sensitivity, and whether prosodic sensitivity is linked to phonological awareness. Prosodic sensitivity was measured by two reiterant speech tasks modelled on Kitzen (2001). The children with developmental dyslexia were significantly impaired in the reiterant speech tasks and in the phonological awareness tasks (onset and rime awareness). There were significant predictive relations between basic auditory processing of amplitude envelope structure (in particular, rise time), prosodic sensitivity, phonological awareness, reading, and spelling. The auditory processing difficulties that characterise children with developmental dyslexia appear to impair their sensitivity to phrase-level prosodic cues such as metrical structure as well as to phonology, but in this study phonological and prosodic sensitivity made largely independent contributions to reading.     

Dyslexia assessment in Arabic

Despite advancements in empirical studies of developmental dyslexia, progress on methods of dyslexia assessment have been hampered by ongoing debate concerning diverse issues such as the role and validity of IQ in the assessment process, labelling and definitions ( Miles, 1994 ; Stanovich, 1991, 1992 ). With the emergence of cross-linguistic studies of dyslexia came the realisation that the manifestation of dyslexia is different in different languages ( Goulandris, 2003 ; Smythe, Everatt & Salter, 2004 ). It follows that the assessment of dyslexia should consider specific linguistic features of the language spoken by the individual to be assessed. This paper argues for the need of culture-fair assessment and calls for considerations to be given when assessing monolingual Arabic-speaking individuals with dyslexia which would take into account the specific linguistic feature of the Arabic language.