The genetics of developmental dyslexia

A data-fusion approach to identifying developmental dyslexia from multi-omics datasets

This exploratory study tested and validated the use of data fusion and machine learning techniques to probe high-throughput omics and clinical data with a goal of exploring the etiology of developmental dyslexia. Developmental dyslexia is the leading learning disability in school aged children affecting roughly 5-10% of the US population. The complex biological and neurological phenotype of this life altering disability complicates its diagnosis. Phenome, exome, and metabolome data was collected allowing us to fully explore this system from a behavioral, cellular, and molecular point of view. This study provides a proof of concept showing that data fusion and ensemble learning techniques can outperform traditional machine learning techniques when provided small and complex multi-omics and clinical datasets. Heterogenous stacking classifiers consisting of single-omic experts/models achieved an accuracy of 86%, F1 score of 0.89, and AUC value of 0.83. Ensemble methods also provided a ranked list of important features that suggests exome single nucleotide polymorphisms found in the thalamus and cerebellum could be potential biomarkers for developmental dyslexia and heavily influenced the classification of DD within our machine learning models.

Human Genomics and the Biocultural Origin of Music

Music is an exclusive feature of humankind. It can be considered as a form of universal communication, only partly comparable to the vocalizations of songbirds. Many trends of research in this field try to address music origins, as well as the genetic bases of musicality. On one hand, several hypotheses have been made on the evolution of music and its role, but there is still debate, and comparative studies suggest a gradual evolution of some abilities underlying musicality in primates. On the other hand, genome-wide studies highlight several genes associated with musical aptitude, confirming a genetic basis for different musical skills which humans show. Moreover, some genes associated with musicality are involved also in singing and song learning in songbirds, suggesting a likely evolutionary convergence between humans and songbirds. This comprehensive review aims at presenting the concept of music as a sociocultural manifestation within the current debate about its biocultural origin and evolutionary function, in the context of the most recent discoveries related to the cross-species genetics of musical production and perception.

The relationship between developmental language disorder and dyslexia in European Portuguese school-aged children

Developmental Language Disorder (DLD) [Also referred to as Specific Language Impairment (SLI)] and dyslexia are neurodevelopmental disorders which show similar behavioral manifestations. In this study, between-group comparisons and frequency analysis were combined to investigate the relationship between DLD and dyslexia. European Portuguese children aged 7-10 years, with DLD (N = 7) or dyslexia (N = 11) were recruited and compared to age-matched typically developing (TD) children (N = 21) on phonological processing, language andf literacy measures. The between-group comparison revealed that for phonological processing, the clinical groups scored significantly below TD children on most tasks, yet the DLD group performed similarly to TD children for RAN speed and digit span. The clinical groups did not statistically differ in their phonological processing abilities. For language abilities, children with dyslexia did not differ from TD children, whilst children with DLD performed significantly below TD children on all measures and significantly below children with dyslexia for vocabulary. Finally, for literacy measures, there were no statistical differences between clinical groups which underperformed on all measures when compared to TD children. The frequency analysis showed that children with DLD exhibited a lower prevalence of RAN difficulties when compared to children with dyslexia, whilst children with DLD tended to show more frequent nonword repetition and phoneme deletion deficits. Additionally, whilst children with DLD consistently showed more prevalent language impairments, both clinical groups demonstrated similar prevalence rates of literacy deficits compared to TD children.These findings lend support to the additional deficit model as children with DLD show more severe and prevalent language impairments than those with dyslexia, despite similar phonological and literacy difficulties.

Assessment for familial pattern and association of polymorphisms in KIAA0319 gene with specific reading disorder in children from North India visiting a tertiary care centre: A case-control study

Genetic association studies have identified KIAA0319 gene as a possible susceptibility locus for reading disorder; however, very few studies are available from India. The study was planned to investigate the familial pattern and association of KIAA0319 polymorphisms among children with reading disorder visiting a tertiary centre in North India. This is a case-control, familial, and genetic association study on 30 children diagnosed with reading disorder (ICD-10) and 30 matched healthy controls and their families. The Aggregate Neurobehavioral Student Health and Educational Review System was administered on parents of probands and controls for reading problems in their siblings, and Adult Reading Questionnaire was administered for parents of both groups. The blood sample was taken from probands, and DNA was isolated. Four KIAA0319 coding sequence single nucleotide polymorphisms (SNPs; rs4504469, rs6935076, rs2038137, and rs2179515) were genotyped using SNaPshot single nucleotide extension. The incidence of reading problem was significantly higher in families of probands as compared with families of controls. There were no significant differences in both groups regarding the frequency of alleles of four SNPs. The reading disorder showed a significant familial pattern, but KIAA0319 gene did not appear to be a susceptibility factor. Future replications with larger samples and whole genome studies are warranted.

Association study of FGF18 with developmental dyslexia in Chinese population

Developmental dyslexia (DD) is a neurobiological disorder featured by reading disabilities. In recent years, genome-wide approaches provided new perspectives to discover novel candidate genes of DD. In a previous study, rs9313548 located downstream of FGF18 showed borderline genome-wide significant association with DD. Herein, we selected rs9313548 and 11 independent tag single nucleotide polymorphisms covering gene region of FGF18 to perform association analysis with DD among 978 Chinese dyslexic cases and 998 controls recruited from elementary schools. However, we did not observe any single nucleotide polymorphism exceeding significant threshold. Our preliminary results suggested that FGF18 might not be a susceptibility gene for DD in Chinese population.

A sequence variant associating with educational attainment also affects childhood cognition

Only a few common variants in the sequence of the genome have been shown to impact cognitive traits. Here we demonstrate that polygenic scores of educational attainment predict specific aspects of childhood cognition, as measured with IQ. Recently, three sequence variants were shown to associate with educational attainment, a confluence phenotype of genetic and environmental factors contributing to academic success. We show that one of these variants associating with educational attainment, rs4851266-T, also associates with Verbal IQ in dyslexic children (P = 4.3 × 10⁻⁴, β = 0.16 s.d.). The effect of 0.16 s.d. corresponds to 1.4 IQ points for heterozygotes and 2.8 IQ points for homozygotes. We verified this association in independent samples consisting of adults (P = 8.3 × 10⁻⁵, β = 0.12 s.d., combined P = 2.2 x 10⁻⁷, β = 0.14 s.d.). Childhood cognition is unlikely to be affected by education attained later in life, and the variant explains a greater fraction of the variance in verbal IQ than in educational attainment (0.7% vs 0.12%,. P = 1.0 × 10⁻⁵).

Opposite Associations between Individual KIAA0319 Polymorphisms and Developmental Dyslexia Risk across Populations: A Stratified Meta-Analysis by the Study Population

KIAA0319 at the DYX2 locus is one of the most extensively studied candidate genes for developmental dyslexia (DD) owing to its important role in neuronal migration. Previous research on associations between KIAA0319 genetic variations and DD has yielded inconsistent results. It is important to establish a more precise estimate of the DD risk associated with these genetic variations. We carried out a meta-analysis of association studies involving KIAA0319 polymorphisms and DD risk. The results of pooled analysis indicated that none of the six investigated markers in or near the KIAA0319 gene are associated with DD. However, a stratified analysis by the study population revealed opposite associations involving KIAA0319 rs4504469 in European and Asian subgroups. The stratified analysis also showed that the KIAA0319 rs9461045 minor allele (T allele) has a protective effect in Asians. This meta-analysis has allowed us to establish the effects of specific KIAA0319 polymorphisms on DD risk with greater precision, as they vary across populations; analyzing one single nucleotide polymorphism at a time could not fully explain the genetic association for DD.

Cognitive and familial risk evidence converged: A data-driven identification of distinct and homogeneous subtypes within the heterogeneous sample of reading disabled children

The evident degree of heterogeneity observed in reading disabled children has puzzled reading researchers for decades. Recent advances in the genetic underpinnings of reading disability have indicated that the heritable, familial risk for dyslexia is a major risk factor. The present data-driven, classification attempt aims to revisit the possibility of identifying distinct cognitive deficit profiles in a large sample of second to fourth grade reading disabled children. In this sample, we investigated whether genetic and environmental risk factors are able to distinguish between poor reader subtypes. In this profile, we included reading-related measures of phonemic awareness, letter-speech sound processing and rapid naming, known as candidate vulnerability markers associated with dyslexia and familial risk for dyslexia, as well as general cognitive abilities (non-verbal IQ and vocabulary). Clustering was based on a 200 multi-start K-means approach. Results revealed four emerging subtypes of which the first subtype showed no cognitive deficits underlying their poor reading skills (Reading-only impaired poor readers). The other three subtypes shared a core phonological deficit (PA) with a variable and discriminative expression across the other underlying vulnerability markers. More specific, type 2 showed low to poor performance across all reading-related and general cognitive abilities (general poor readers), type 3 showed a specific letter-speech sound mapping deficit next to a PA deficit (PA-LS specific poor readers) and type 4 showed a specific rapid naming deficit complementing their phonological weakness (PA-RAN specific poor readers). The first three poor reader profiles were more characterized by variable environmental risk factor, while the fourth, PA-RAN poor reader subtype showed a significantly strong familial risk for dyslexia. Overall, when we zoom in on the heterogeneous phenomenon of reading disability, unique and distinct cognitive subtypes can be identified, distinguishing between those poor readers more influences by the role of genes and those more influenced by environmental risk factors. Taking into account this diversity of distinct cognitive subtypes, instead of looking at the reading disabled sample as a whole, will help tailor future diagnostic and intervention efforts more specifically to the needs of children with such a specific deficit and risk pattern, as well as providing a more promising way forward for genetic studies of dyslexia.

The Adult Reading History Questionnaire (ARHQ) in Icelandic: Psychometric Properties and Factor Structure

This article describes psychometric testing of an Icelandic adaptation of the Adult Reading History Questionnaire (ARHQ), designed to detect a history of reading difficulties indicative of dyslexia. Tested in a large and diverse sample of 2,187 adults, the Icelandic adaptation demonstrated internal consistency reliability (Cronbach's alpha = .92) and test-retest reliability (r = .93). Validity was established by comparing scores of adults who as children received ICD-10 diagnoses of specific reading disorder (F81.0; n = 419) to those of adults defined as nondyslexics (n = 679). ROC curve analysis resulted in an area under the curve of .92 (95% CI = .90, .93, p < .001) and a cutoff score of .43 with sensitivity of 84.5% and specificity of 83.7%. An exploratory factor analysis (n = 2,187) suggested three subscales, Dyslexia Symptoms, Current Reading, and Memory, the mean scores of which differed significantly among diagnosed dyslexics, relatives of dyslexics, and population controls. Our results support the applicability of the ARHQ in Icelandic as a self-report screening tool for adult dyslexia in Iceland.

Dyslexia: the Role of Vision and Visual Attention

Dyslexia is more than just difficulty with translating letters into sounds. Many dyslexics have problems with clearly seeing letters and their order. These difficulties may be caused by abnormal development of their visual “magnocellular” (M) nerve cells; these mediate the ability to rapidly identify letters and their order because they control visual guidance of attention and of eye fixations. Evidence for M cell impairment has been demonstrated at all levels of the visual system: in the retina, in the lateral geniculate nucleus, in the primary visual cortex and throughout the dorsal visuomotor “where” pathway forward from the visual cortex to the posterior parietal and prefrontal cortices. This abnormality destabilises visual perception; hence, its severity in individuals correlates with their reading deficit. Treatments that facilitate M function, such as viewing text through yellow or blue filters, can greatly increase reading progress in children with visual reading problems. M weakness may be caused by genetic vulnerability, which can disturb orderly migration of cortical neurones during development or possibly reduce uptake of omega-3 fatty acids, which are usually obtained from fish oils in the diet. For example, M cell membranes require replenishment of the omega-3 docosahexaenoic acid to maintain their rapid responses. Hence, supplementing some dyslexics’ diets with DHA can greatly improve their M function and their reading.

Association of SNPs of DYX1C1 with developmental dyslexia in an Indian population

OBJECTIVE

DYX1C1 has been identified as a susceptible candidate gene for developmental dyslexia (DD); studies in various populations have yielded inconclusive results and the causal allele is unknown in the Indian population. On the basis of the initial association studies and the role of DYX1C1 in neuronal migration, we investigated the role of DYX1C1 in causing DD in an Indian population.

MATERIALS AND METHODS

Ten single-nucleotide polymorphisms (SNPs) of DYX1C1 were genotyped in 210 cases with DD and 256 age-matched nondyslexic controls. Genotyping of these SNPs was carried with the MassARRAY technique using SpectroCHIP and analysed with MALDI-TOF MS. Single-marker and two-marker haplotype analyses were carried out and the χ-test, odds ratios, 95% confidence intervals and Yates correction were applied to identify the significance of the genotyped SNPs.

RESULTS

A significant association was observed for the homozygous genotype (GG) of the SNP rs12899331 (3.12%) and individual allele frequency (P=0.039). Psycholinguistic tests showed an association between rs12899331 with dyslexic phenotypes such as word and nonword reading, syllable reversal task, spoonerism task and spelling. Two-marker haplotype analysis also showed a significant association for the markers G/C at rs12899331/rs1075938 (P=0.039) with the phenotypes rapid naming ability and phonological awareness, as well as with word reading, spelling and sentence repetition.

CONCLUSION

The promoter SNP rs12899331 of DYX1C1 may contribute towards the manifestation of DD. This study supports the association of DYX1C1 with DD in an Indian population.

Postural control is not systematically related to reading skills: implications for the assessment of balance as a risk factor for developmental dyslexia

Impaired postural control has been associated with poor reading skills, as well as with lower performance on measures of attention and motor control variables that frequently co-occur with reading difficulties. Measures of balance and motor control have been incorporated into several screening batteries for developmental dyslexia, but it is unclear whether the relationship between such skills and reading manifests as a behavioural continuum across the range of abilities or is restricted to groups of individuals with specific disorder phenotypes. Here were obtained measures of postural control alongside measures of reading, attention and general cognitive skills in a large sample of young adults (n = 100). Postural control was assessed using centre of pressure (CoP) measurements, obtained over 5 different task conditions. Our results indicate an absence of strong statistical relationships between balance measures with either reading, cognitive or attention measures across the sample as a whole.

Lack of association between genetic polymorphisms in ROBO1, MRPL19/C2ORF3 and THEM2 with developmental dyslexia

Developmental Dyslexia (DD) is a heritable, complex genetic disorder characterized by specific impairment in reading and writing ability that is substantially below the expected reading ability given the person's chronological age, measured intelligence and age-appropriate education. More than ten susceptible genes have been identified for DD. A Single Nucleotide Polymorphism (SNP) of these genes was found to be associated with various phenotypes of DD. To identify the role of SNPs of four candidate genes namely, MRPL19/C2ORF3, ROBO1 and THEM2 in an Indian population, we genotyped eight SNPs of these genes in 157 children with DD and 212 normal readers using a MassARRAY technique with a MALDI-TOF MS analyzer. Power analysis of some of these SNPs showed >80% of power. Chi-square test, Odds Ratios (ORs), 95% Confidence Intervals (CIs) and Bonferroni's correction were applied to identify the significance of the genotyped SNPs and haplotypes. Our study failed to show any association of SNPs and haplotypes of these genes with DD in an Indian population.

Genetic analysis of dyslexia candidate genes in the European cross-linguistic NeuroDys cohort

Dyslexia is one of the most common childhood disorders with a prevalence of around 5-10% in school-age children. Although an important genetic component is known to have a role in the aetiology of dyslexia, we are far from understanding the molecular mechanisms leading to the disorder. Several candidate genes have been implicated in dyslexia, including DYX1C1, DCDC2, KIAA0319, and the MRPL19/C2ORF3 locus, each with reports of both positive and no replications. We generated a European cross-linguistic sample of school-age children - the NeuroDys cohort - that includes more than 900 individuals with dyslexia, sampled with homogenous inclusion criteria across eight European countries, and a comparable number of controls. Here, we describe association analysis of the dyslexia candidate genes/locus in the NeuroDys cohort. We performed both case-control and quantitative association analyses of single markers and haplotypes previously reported to be dyslexia-associated. Although we observed association signals in samples from single countries, we did not find any marker or haplotype that was significantly associated with either case-control status or quantitative measurements of word-reading or spelling in the meta-analysis of all eight countries combined. Like in other neurocognitive disorders, our findings underline the need for larger sample sizes to validate possibly weak genetic effects.

Analysis of genetic variants of dyslexia candidate genes KIAA0319 and DCDC2 in Indian population

Developmental dyslexia (DD) is a heritable, complex genetic disorder associated with impairment in reading and writing skills despite having normal intellectual ability and appropriate educational opportunities. Chromosome 6p23-21.3 at DYX2 locus has showed the most consistent evidence of linkage for DD and two susceptible genes KIAA0319 and DCDC2 for DD at DYX2 locus showed significant association. Specific candidate gene-association studies have identified variants, risk haplotypes and microsatellites of KIAA0319 and DCDC2 correlated with wide range of reading-related traits. In this study, we used a case-control approach for analyzing single-nucleotide polymorphisms (SNPs) in KIAA0319 and DCDC2. Our study demonstrated the association of DD with SNP rs4504469 of KIAA0319 and not with any SNPs of DCDC2.

Transcriptional program of ciliated epithelial cells reveals new cilium and centrosome components and links to human disease

Defects in the centrosome and cilium are associated with a set of human diseases having diverse phenotypes. To further characterize the components that define the function of these organelles we determined the transcriptional profile of multiciliated tracheal epithelial cells. Cultures of mouse tracheal epithelial cells undergoing differentiation in vitro were derived from mice expressing GFP from the ciliated-cell specific FOXJ1 promoter (FOXJ1:GFP). The transcriptional profile of ciliating GFP+ cells from these cultures was defined at an early and a late time point during differentiation and was refined by subtraction of the profile of the non-ciliated GFP- cells. We identified 649 genes upregulated early, when most cells were forming basal bodies, and 73 genes genes upregulated late, when most cells were fully ciliated. Most, but not all, of known centrosome proteins are transcriptionally upregulated early, particularly Plk4, a master regulator of centriole formation. We found that three genes associated with human disease states, Mdm1, Mlf1, and Dyx1c1, are upregulated during ciliogenesis and localize to centrioles and cilia. This transcriptome for mammalian multiciliated epithelial cells identifies new candidate centrosome and cilia proteins, highlights similarities between components of motile and primary cilia, and identifies new links between cilia proteins and human disease.

Probing the neurocognitive trajectories of children's reading skills

Emerging evidence of the high variability in the cognitive skills and deficits associated with reading achievement and dysfunction promotes both a more dimensional view of the risk factors involved, and the importance of discriminating between trajectories of impairment. Here we examined reading and component orthographic and phonological skills alongside measures of cognitive ability and auditory and visual sensory processing in a large group of primary school children between the ages of 7 and 12 years. We identified clusters of children with pseudoword or exception word reading scores at the 10th percentile or below relative to their age group, and a group with poor skills on both tasks. Compared to age-matched and reading-level controls, groups of children with more impaired exception word reading were best described by a trajectory of developmental delay, whereas readers with more impaired pseudoword reading or combined deficits corresponded more with a pattern of atypical development. Sensory processing deficits clustered within both of the groups with putative atypical development: auditory discrimination deficits with poor phonological awareness skills; impairments of visual motion processing in readers with broader and more severe patterns of reading and cognitive impairments. Sensory deficits have been variably associated with developmental impairments of literacy and language; these results suggest that such deficits are also likely to cluster in children with particular patterns of reading difficulty.

Dissection of genetic associations with language-related traits in population-based cohorts

Recent advances in the field of language-related disorders have led to the identification of candidate genes for specific language impairment (SLI) and dyslexia. Replication studies have been conducted in independent samples including population-based cohorts, which can be characterised for a large number of relevant cognitive measures. The availability of a wide range of phenotypes allows us to not only identify the most suitable traits for replication of genetic association but also to refine the associated cognitive trait. In addition, it is possible to test for pleiotropic effects across multiple phenotypes which could explain the extensive comorbidity observed across SLI, dyslexia and other neurodevelopmental disorders. The availability of genome-wide genotype data for such cohorts will facilitate this kind of analysis but important issues, such as multiple test corrections, have to be taken into account considering that small effect sizes are expected to underlie such associations.

Are balance problems connected to reading speed or the familial risk of dyslexia?

AIM

The aim of this study was to examine the connection between balance problems and reading speed in children with and without a familial risk of dyslexia by controlling for the effects of attention, hyperactivity, and cognitive and motor functioning.

METHOD

The prevalence of balance problems was studied in 94 children (48 females, 46 males) with a familial risk of dyslexia (at-risk group) and 85 children (38 females, 47 males) without a risk of dyslexia (comparison group). Further, the relationships between balance problems (at age 8y 6mo), reading proficiency (at age 9y), attention-deficit-hyperactivity disorder (at age 8y), and cognitive (at age 8y 6mo) and motor functioning (at age 6y 6mo) were examined. Inclusion criteria for the at-risk group were that at least one parent had a confirmed reading problem and one or more of the parents' close relatives also had a reading problem. The Good Balance System was used to assess static standing balance, word-list and text reading tasks were used to measure reading proficiency. The Behavioural Assessment System for Children - Parent Rating Scale was used to assess attention-deficit-hyperactivity disorder, the Wechsler Intelligence Scale for Children was used to assess cognitive functioning, and the Movement Assessment Battery for Children was used to measure motor functioning.

RESULTS

Balance (F((1,177)) =4.82; p=0.029; =0.027) and reading (F((1,176)) =11.95; p=0.001; =0.064) problems were more common in the at-risk group than in the comparison group. Furthermore, attention, hyperactivity, IQ, and motor functioning were not related to balance problems. However, attention (F((1,154)) =10.80; p=0.001; =0.066) and IQ (F((1,170)) =22.08; p<0.001; =0.115) were individually connected to reading speed.

INTERPRETATION

Balance problems alone could not produce any differences in reading skills. Instead, both balance problems and reduced reading skills were mainly associated separately with a familial risk of dyslexia. This indicates that there may be a shared genetic mechanism between balance and reading problems.

Investigation of dyslexia and SLI risk variants in reading- and language-impaired subjects

Dyslexia (or reading disability) and specific language impairment (or SLI) are common childhood disorders that show considerable co-morbidity and diagnostic overlaps and have been suggested to share some genetic aetiology. Recently, genetic risk variants have been identified for SLI and dyslexia enabling the direct evaluation of possible shared genetic influences between these disorders. In this study we investigate the role of variants in these genes (namely MRPL19/C20RF3, ROBO1, DCDC2, KIAA0319, DYX1C1, CNTNAP2, ATP2C2 and CMIP) in the aetiology of SLI and dyslexia. We perform case-control and quantitative association analyses using measures of oral and written language skills in samples of SLI and dyslexic families and cases. We replicate association between KIAA0319 and DCDC2 and dyslexia and provide evidence to support a role for KIAA0319 in oral language ability. In addition, we find association between reading-related measures and variants in CNTNAP2 and CMIP in the SLI families.

Investigation of dyslexia and SLI risk variants in reading- and language-impaired subjects

Dyslexia (or reading disability) and specific language impairment (or SLI) are common childhood disorders that show considerable co-morbidity and diagnostic overlaps and have been suggested to share some genetic aetiology. Recently, genetic risk variants have been identified for SLI and dyslexia enabling the direct evaluation of possible shared genetic influences between these disorders. In this study we investigate the role of variants in these genes (namely MRPL19/C20RF3, ROBO1, DCDC2, KIAA0319, DYX1C1, CNTNAP2, ATP2C2 and CMIP) in the aetiology of SLI and dyslexia. We perform case-control and quantitative association analyses using measures of oral and written language skills in samples of SLI and dyslexic families and cases. We replicate association between KIAA0319 and DCDC2 and dyslexia and provide evidence to support a role for KIAA0319 in oral language ability. In addition, we find association between reading-related measures and variants in CNTNAP2 and CMIP in the SLI families.

Is season of birth related to developmental dyslexia?

Different moderators/mediators of risk are involved in developmental dyslexia (DD), but data are inconsistent. We explored the prevalence of season of birth and its association with gender and age of school entry in an Italian sample of dyslexic children compared to an Italian normal control group. The clinical sample included 498 children (345 boys, mean age 10.3 ± 2.1 years) with DD, the control sample 1,276 children (658 boys, mean age 10.8 ± 2.2 years) from four elementary schools from the same urban area, and with the same socio-economic status level. A prevalence of birth in autumn was found among children with DD compared to controls (34% versus 24%, p < 0.0001). Children with DD were more frequently males (p < 0.0001) and had a lower mean age of school entry (p < 0.0001). Regarding the distribution of ages, 11.4% of children with DD, but none of the subjects in the control group, started school before 5.7 years. Therefore, greater risk of DD was related to age of school entry (OR = 2.72), gender (OR = 2.16), and season of birth (OR = 1.21). Significant interactions between boys with DD born in autumn, and correct school of entry (OR = 2.56) were joint predictors of higher risk of DD. The association between birth in autumn and DD may be explained by the earlier age of school entry, which may be a critical element in the youngest children with DD or at risk to DD. Whether Italian school policy is oriented to anticipate the school entry, a closer detection of early learning disorders and associated risk factors (familial load, specific language disorders, and attention deficit hyperactivity disorder) should be warranted.

Identification of candidate genes for dyslexia susceptibility on chromosome 18

BACKGROUND

Six independent studies have identified linkage to chromosome 18 for developmental dyslexia or general reading ability. Until now, no candidate genes have been identified to explain this linkage. Here, we set out to identify the gene(s) conferring susceptibility by a two stage strategy of linkage and association analysis.

METHODOLOGY/PRINCIPAL FINDINGS

Linkage analysis: 264 UK families and 155 US families each containing at least one child diagnosed with dyslexia were genotyped with a dense set of microsatellite markers on chromosome 18. Association analysis: Using a discovery sample of 187 UK families, nearly 3000 SNPs were genotyped across the chromosome 18 dyslexia susceptibility candidate region. Following association analysis, the top ranking SNPs were then genotyped in the remaining samples. The linkage analysis revealed a broad signal that spans approximately 40 Mb from 18p11.2 to 18q12.2. Following the association analysis and subsequent replication attempts, we observed consistent association with the same SNPs in three genes; melanocortin 5 receptor (MC5R), dymeclin (DYM) and neural precursor cell expressed, developmentally down-regulated 4-like (NEDD4L).

CONCLUSIONS

Along with already published biological evidence, MC5R, DYM and NEDD4L make attractive candidates for dyslexia susceptibility genes. However, further replication and functional studies are still required.

Genetics of developmental dyslexia

Developmental dyslexia is a highly heritable disorder with a prevalence of at least 5% in school-aged children. Linkage studies have identified numerous loci throughout the genome that are likely to harbour candidate dyslexia susceptibility genes. Association studies and the refinement of chromosomal translocation break points in individuals with dyslexia have resulted in the discovery of candidate genes at some of these loci. A key function of many of these genes is their involvement in neuronal migration. This complements anatomical abnormalities discovered in dyslexic brains, such as ectopias, that may be the result of irregular neuronal migration.

Dyslexia and DCDC2: normal variation in reading and spelling is associated with DCDC2 polymorphisms in an Australian population sample

The 6p21-p22 chromosomal region has been identified as a developmental dyslexia locus both in linkage and association studies, the latter generating evidence for the doublecortin domain containing 2 (DCDC2) as a candidate gene at this locus (and also for KIAA0319). Here, we report an association between DCDC2 and reading and spelling ability in 522 families of adolescent twins unselected for reading impairment. Family-based association was conducted on 21 single nucleotide polymorphisms (SNPs) in DCDC2 using quantitative measures of lexical processing (irregular-word reading), phonological decoding (non-word reading) and spelling-based measures of dyslexia derived from the Components of Reading Examination test. Significant support for association was found for rs1419228 with regular-word reading and spelling (P=0.002) as well as irregular-word reading (P=0.004), whereas rs1091047 was significantly associated (P=0.003) with irregular-word reading (a measure of lexical storage). Four additional SNPs (rs9467075, rs9467076, rs7765678 and rs6922023) were nominally associated with reading and spelling. This study provides support for DCDC2 as a risk gene for reading disorder, and suggests that this risk factor acts on normally varying reading skill in the general population.

Convergent genetic linkage and associations to language, speech and reading measures in families of probands with Specific Language Impairment

We analyzed genetic linkage and association of measures of language, speech and reading phenotypes to candidate regions in a single set of families ascertained for SLI. Sib-pair and family-based analyses were carried out for candidate gene loci for Reading Disability (RD) on chromosomes 1p36, 3p12-q13, 6p22, and 15q21, and the speech-language candidate region on 7q31 in a sample of 322 participants ascertained for Specific Language Impairment (SLI). Replication or suggestive replication of linkage was obtained in all of these regions, but the evidence suggests that the genetic influences may not be identical for the three domains. In particular, linkage analysis replicated the influence of genes on chromosome 6p for all three domains, but association analysis indicated that only one of the candidate genes for reading disability, KIAA0319, had a strong effect on language phenotypes. The findings are consistent with a multiple gene model of the comorbidity between language impairments and reading disability and have implications for neurocognitive developmental models and maturational processes.

Two functions of early language experience

The unique human ability of linguistic communication, defined as the ability to produce a practically infinite number of meaningful messages using a finite number of lexical items, is determined by an array of "linguistic" genes, which are expressed in neurons forming domain-specific linguistic centers in the brain. In this review, I discuss the idea that infants' early language experience performs two complementary functions. In addition to allowing infants to assimilate the words and grammar rules of their mother language, early language experience initiates genetic programs underlying language production and comprehension. This hypothesis explains many puzzling characteristics of language acquisition, such as the existence of a critical period for acquiring the first language and the absence of a critical period for the acquisition of additional language(s), a similar timetable for language acquisition in children belonging to families of different social and cultural status, the strikingly similar timetables in the acquisition of oral and sign languages, and the surprisingly small correlation between individuals' final linguistic competence and the intensity of their training. Based on the studies of microcephalic individuals, I argue that genetic factors determine not only the number of neurons and organization of interneural connections within linguistic centers, but also the putative internal properties of neurons that are not limited to their electrophysiological and synaptic properties.

The dyslexia-associated protein KIAA0319 interacts with adaptor protein 2 and follows the classical clathrin-mediated endocytosis pathway

Recently, genetic studies have implicated KIAA0319 in developmental dyslexia, the most common of the childhood learning disorders. The first functional data indicated that the KIAA0319 protein is expressed on the plasma membrane and may be involved in neuronal migration. Further analysis of the subcellular distribution of the overexpressed protein in mammalian cells indicates that KIAA0319 can colocalize with the early endosomal marker early endosome antigen 1 (EEA1) in large intracellular vesicles, suggesting that it is endocytosed. Antibody internalization assays with full-length KIAA0319 and deletion constructs confirmed that KIAA0319 is internalized and showed the importance of the cytoplasmic juxtamembranal region in this process. The present study has identified the medium subunit (μ2) of adaptor protein 2 (AP-2) as a binding partner of KIAA0319 in a yeast two-hybrid screen. Using Rab5 mutants or depletion of the μ-subunit of AP-2 or clathrin heavy chain by RNA interference, we demonstrate that KIAA0319 follows a clathrin-mediated endocytic pathway. We also identify tyrosine-995 of KIAA0319 as a critical amino acid required for the interaction with AP-2 and subsequent internalization. These results suggest the surface expression of KIAA0319 is regulated by endocytosis, supporting the idea that the internalization and recycling of the protein may be involved in fine tuning its role in neuronal migration.

The genetics of reading disability

Genetic factors contribute substantially to the development of reading disability (RD). Family linkage studies have implicated many chromosomal regions containing RD susceptibility genes, of which putative loci at 1p34-p36 (DYX8), 2p (DYX3), 6p21.3 (DYX2), and 15q21 (DYX1) have been frequently replicated, whereas those at 3p12-q12 (DYX5), 6q13-q16 (DYX4), 11p15 (DYX7), 18p11 (DYX6), and Xq27 (DYX9) have less evidence. Association studies of positional candidate genes have implicated DCDC2 and KIAA0319 in DYX2, as well as C2ORF3 and MRPL19 (DYX3), whereas DYX1C1/EKN1 (DYX1) and ROBO1 (DYX5) were found to be disrupted by rare translocation breakpoints in reading-disabled individuals. Four of the candidate genes (DYX1C1, KIAA0319, DCDC2, and ROBO1) appear to function in neuronal migration and guidance, suggesting the importance of early neurodevelopmental processes in RD. Future studies to help us understand the function of these and other RD candidate genes promise to yield enormous insight into the neurobiologic mechanisms underlying the pathophysiology of this disorder.

Association of ADHD and the Protogenin gene in the chromosome 15q21.3 reading disabilities linkage region

Twin studies indicate genetic overlap between symptoms of attention deficit hyperactivity disorder (ADHD) and reading disabilities (RD), and linkage studies identify several chromosomal regions possibly containing common susceptibility genes, including the 15q region. Based on a translocation finding and association to two specific alleles, the candidate gene, DYX1C1, has been proposed as the susceptibility gene for RD in 15q. Previously, we tested markers in DYX1C1 for association with ADHD. Although we identified association for haplotypes across the gene, we were unable to replicate the association to the specific alleles reported. Thus, the risk alleles for ADHD are yet to be identified. The susceptibility alleles may be in a remote regulatory element, or DYX1C1 may not be the risk gene. To continue study of 15q, we tested a coding region change in DYX1C1, followed by markers across the gene Protogenin (PRTG) in 253 ADHD nuclear families. PRTG was chosen based on its location and because it is closely related to DCC and Neogenin, two genes known to guide migratory cells and axons during development. The markers in DYX1C1 were not associated to ADHD when analyzed individually; however, six markers in PRTG showed significant association with ADHD as a categorical trait (P = 0.025-0.005). Haplotypes in both genes showed evidence for association. We identified association with ADHD symptoms measured as quantitative traits in PRTG, but no evidence for association with two key components of reading, word identification and decoding was observed. These findings, while preliminary, identify association of ADHD to a gene that potentially plays a role in cell migration and axon growth.

Quantitative trait locus association scan of early reading disability and ability using pooled DNA and 100K SNP microarrays in a sample of 5760 children

Quantitative genetic research suggests that reading disability is the quantitative extreme of the same genetic and environmental factors responsible for normal variation in reading ability. This finding warrants a quantitative trait locus (QTL) strategy that compares low versus high extremes of the normal distribution of reading in the search for QTLs associated with variation throughout the distribution. A low reading ability group (N=755) and a high reading group (N=747) were selected from a representative UK sample of 7-year-olds assessed on two measures of reading that we have shown to be highly heritable and highly genetically correlated. The low and high reading ability groups were each divided into 10 independent DNA pools and the 20 pools were assayed on 100 K single nucleotide polymorphism (SNP) microarrays to screen for the largest allele frequency differences between the low and high reading ability groups. Seventy five of these nominated SNPs were individually genotyped in an independent sample of low (N=452) and high (N=452) reading ability children selected from a second sample of 4258 7-year-olds. Nine of the seventy-five SNPs were nominally significant (P<0.05) in the predicted direction. These 9 SNPs and 14 other SNPs showing low versus high allele frequency differences in the predicted direction were genotyped in the rest of the second sample to test the QTL hypothesis. Ten SNPs yielded nominally significant linear associations in the expected direction across the distribution of reading ability. However, none of these SNP associations accounted for more than 0.5% of the variance of reading ability, despite 99% power to detect them. We conclude that QTL effect sizes, even for highly heritable common disorders and quantitative traits such as early reading disability and ability, might be much smaller than previously considered.

Genome-wide linkage scan for loci of musical aptitude in Finnish families: evidence for a major locus at 4q22

Background:

Music perception and performance are comprehensive human cognitive functions and thus provide an excellent model system for studying human behaviour and brain function. However, the molecules involved in mediating music perception and performance are so far uncharacterised.

Objective:

To unravel the biological background of music perception, using molecular and statistical genetic approaches.

Methods: 15 Finnish multigenerational families (with a total of 234 family members) were recruited via a nationwide search. The phenotype of all family members was determined using three tests used in defining musical aptitude: a test for auditory structuring ability (Karma Music test; KMT) commonly used in Finland, and the Seashore pitch and time discrimination subtests (SP and ST respectively) used internationally. We calculated heritabilities and performed a genome-wide variance components-based linkage scan using genotype data for 1113 microsatellite markers.

Results:

The heritability estimates were 42% for KMT, 57% for SP, 21% for ST and 48% for the combined music test scores. Significant evidence of linkage was obtained on chromosome 4q22 (LOD 3.33) and suggestive evidence of linkage at 8q13-21 (LOD 2.29) with the combined music test scores, using variance component linkage analyses. The major contribution of the 4q22 locus was obtained for the KMT (LOD 2.91). Interestingly, a positive LOD score of 1.69 was shown at 18q, a region previously linked to dyslexia (DYX6) using combined music test scores.

Conclusion:

Our results show that there is a genetic contribution to musical aptitude that is likely to be regulated by several predisposing genes or variants.

Colorado longitudinal twin study of reading disability

The primary objectives of the present study are to introduce the Colorado Longitudinal Twin Study of Reading Disability, the first longitudinal twin study in which subjects have been specifically selected for having a history of reading difficulties, and to present some initial assessments of the stability of reading performance and cognitive abilities in this sample. Preliminary examination of the test scores of 124 twins with a history of reading difficulties and 154 twins with no history of reading difficulties indicates that over the 5- to 6-year interval between assessments, cognitive and reading performance are highly stable. As a group, those subjects with a history of reading difficulties had substantial deficits relative to control subjects on all measures at initial assessment, and significant deficits remained at follow-up. The stability noted for all cognitive and achievement measures was highest for a composite measure of reading, whose average stability correlation across groups was 0.80. Results of preliminary behavior genetic analyses for this measure indicated that shared genetic influences accounted for 86% and 49% of the phenotypic correlations between the two assessments for twin pairs with and without reading difficulties, respectively. In addition, genetic correlations reached unity for both groups, suggesting that the same genetic influences are manifested at both time points.

Alternative splicing in the dyslexia-associated gene KIAA0319

The KIAA0319 gene in chromosome 6p22 has been strongly associated with developmental dyslexia. In this article we show a wide expression pattern of this gene in human adult brain by Northern blot analysis. We also performed RT-PCR analysis to detect alternative splicing variants in human brain. Most of the detected variants involve alternative splicing of the exons at the 5' and the 3' ends. Two main forms differing in the length of the 5' UTR are detected at approximately the same rate. Two variants (B and C) lacking exon 19, which encodes the transmembrane domain, are the main alternative forms detected among those predicted to encode protein. These two variants could be secreted and might be involved in signaling functions. A similar RT-PCR analysis performed in mouse and rat adult brains showed that only some of the alternative splicing variants are equivalent to those found in the human gene.

High risk of reading disability and speech sound disorder in rolandic epilepsy families: case-control study

PURPOSE

Associations between rolandic epilepsy (RE) with reading disability (RD) and speech sound disorder (SSD) have not been tested in a controlled study. We conducted a case-control study to determine whether (1) RD and SSD odds are higher in RE probands than controls and (2) an RE proband predicts a family member with RD or SSD, hence suggesting a shared genetic etiology for RE, RD, and SSD.

METHODS

Unmatched case-control study with 55 stringently defined RE cases, 150 controls in the same age range lacking a primary brain disorder diagnosis, and their siblings and parents. Odds ratios (OR) were calculated by multiple logistic regression, adjusted for sex and age, and for relatives, also adjusted for comorbidity of RD and SSD in the proband.

RESULTS

RD was strongly associated with RE after adjustment for sex and age: OR 5.78 (95% CI: 2.86-11.69). An RE proband predicts RD in family members: OR 2.84 (95% CI: 1.38-5.84), but not independently of the RE proband's RD status: OR 1.30 (95% CI: 0.55-12.79). SSD was also comorbid with RE: adjusted OR 2.47 (95%CI: 1.22-4.97). An RE proband predicts SSD in relatives, even after controlling for sex, age and proband SSD comorbidity: OR 4.44 (95% CI: 1.93-10.22).

CONCLUSIONS

RE is strongly comorbid with RD and SSD. Both RD and SSD are likely to be genetically influenced and may contribute to the complex genetic etiology of the RE syndrome. Siblings of RE patients are at high risk of RD and SSD and both RE patients and their younger siblings should be screened early.

The Genetic Lexicon of Dyslexia

Reading abilities are acquired only through specific teaching and training. A significant proportion of children fail to achieve these skills despite normal intellectual abilities and an appropriate opportunity to learn. Difficulty in learning to read is attributable to specific dysfunctions of the brain, which so far remain poorly understood. However, it is recognized that the neurological basis for dyslexia, or reading disability, is caused in large part by genetic factors. Linkage studies have successfully identified several regions of the human genome that are likely to harbor susceptibility genes for dyslexia. In the past few years there have been exciting advances with the identification of four candidate genes located within three of these linked chromosome regions: DYX1C1 on chromosome 15, ROBO1 on chromosome 3, and KIAA0319 and DCDC2 on chromosome 6. Functional studies of these genes are offering new insights about the biological mechanisms underlying the development of dyslexia and, in general, of cognition.

A case for genetics education: collaborating with speech-language pathologists and audiologists

Because speech-language pathologists (SLPs) and audiologists (AUDs) are among the first referrals for parents of children exhibiting feeding, speech, language, hearing, and balance difficulties, it is important for SLP and AUD professionals to recognize genetic causes of and contributions to complex and Mendelian communication disorders. We review genetics in the curricula of speech-language pathology and audiology programs and obstacles to its integration throughout curricula. We present suggestions about how SLPs and AUDs can aid in diagnosis and contribute their clinical expertise in characterizing phenotypes, followed with a review of a new genetics-education website developed by the National Coalition for Health Professional Education in Genetics (NCHPEG), the University of Cincinnati, and the National Society of Genetic Counselors. The need to integrate genetics content into curricula and continuing education across disciplines is clear, as is the need for and benefit of multidisciplinary collaboration in patient care. The NCHPEG site for speech-language pathology and audiology begins to address those needs and may serve as a practical model for future multidisciplinary collaborations between genetics professionals and other health professions.

Further evidence that the KIAA0319 gene confers susceptibility to developmental dyslexia

The DYX2 locus on chromosome 6p22.2 is the most replicated region of linkage to developmental dyslexia (DD). Two candidate genes within this region have recently been implicated in the disorder: KIAA0319 and DCDC2. Variants within DCDC2 have shown association with DD in a US and a German sample. However, when we genotyped these specific variants in two large, independent UK samples, we obtained only weak, inconsistent evidence for their involvement in DD. Having previously found evidence that variation in the KIAA0319 gene confers susceptibility to DD, we sought to refine this genetic association by genotyping 36 additional SNPs in the gene. Nine SNPs, predominantly clustered around the first exon, showed the most significant association with DD in one or both UK samples, including rs3212236 in the 5' flanking region (P = 0.00003) and rs761100 in intron 1 (P = 0.0004). We have thus refined the region of association with developmental dyslexia to putative regulatory sequences around the first exon of the KIAA0319 gene, supporting the presence of functional mutations that could affect gene expression. Our data also suggests a possible interaction between KIAA0319 and DCDC2, which requires further testing.

Replication of reported linkages for dyslexia and spelling and suggestive evidence for novel regions on chromosomes 4 and 17

We report the first genome-wide linkage analysis for reading and spelling in a sample of 403 families of twins, aged between 12 and 25 years taken from the normal population and unselected for reading ability. These traits showed heritabilities of 0.52-0.73, and support for linkage exceeded replication levels (lod > 1.44) of seven of the 11 linkages reported in dyslexic samples, namely: 2q22.3, 3p12-q13, 6q11.2, 7q32, 15q21.1, 18p21, and Xq27.3. For five of these (2q22.3, 6q11.2, 7q32, 18p21, and Xq27), this study provides the first independent replication. 1p34-36 and 2p15-16 received some support, with lods of 1.2 and 0.83, respectively, whereas two regions received little support (6p23-21.3 and 11p15.5). This study also identified two novel linkages at 4p15.33-16.1 and 17p13.3, which received suggestive support (max. lod 2.08 and 1.99, respectively).

“Scientific roots” of dualism in neuroscience

Although the dualistic concept is unpopular among neuroscientists involved in experimental studies of the brain, neurophysiological literature is full of covert dualistic statements on the possibility of understanding neural mechanisms of human consciousness. Particularly, the covert dualistic attitude is exhibited in the unwillingness to discuss neural mechanisms of consciousness, leaving the problem of consciousness to psychologists and philosophers. This covert dualism seems to be rooted in the main paradigm of neuroscience that suggests that cognitive functions, such as language production and comprehension, face recognition, declarative memory, emotions, etc., are performed by neural networks consisting of simple elements. I argue that neural networks of any complexity consisting of neurons whose function is limited to the generation of electrical potentials and the transmission of signals to other neurons are hardly capable of producing human mental activity, including consciousness. Based on results obtained in physiological, morphological, clinical, and genetic studies of cognitive functions (mainly linguistic ones), I advocate the hypothesis that the performance of cognitive functions is based on complex cooperative activity of "complex" neurons that are carriers of "elementary cognition." The uniqueness of human cognitive functions, which has a genetic basis, is determined by the specificity of genes expressed by these "complex" neurons. The main goal of the review is to show that the identification of the genes implicated in cognitive functions and the understanding of a functional role of their products is a possible way to overcome covert dualism in neuroscience.