A genomewide scan identifies two novel loci involved in specific language impairment

Gene × Environment interactions in speech sound disorder predict language and preliteracy outcomes

Few studies have investigated the role of gene × environment interactions (G × E) in speech, language, and literacy disorders. Currently, there are two theoretical models, the diathesis–stress model and the bioecological model, that make opposite predictions about the expected direction of G × E, because environmental risk factors may either strengthen or weaken the effect of genes on phenotypes. The purpose of the current study was to test for G × E at two speech sound disorder and reading disability linkage peaks using a sib-pair linkage design and continuous measures of socioeconomic status, home language/literacy environment, and number of ear infections. The interactions were tested using composite speech, language, and preliteracy phenotypes and previously identified linkage peaks on 6p22 and 15q21. Results showed five G × E at both the 6p22 and 15q21 locations across several phenotypes and environmental measures. Four of the five interactions were consistent with the bioecological model of G × E. Each of these four interactions involved environmental measures of the home language/literacy environment. The only interaction that was consistent with the diathesis–stress model was one involving the number of ear infections as the environmental risk variable. The direction of these interactions and possible interpretations are explored in the discussion.

A review of association and linkage studies for genetical analyses of learning disorders

Learning disorders (LD) commonly comprise of a heterogeneous group of disorders manifested by unexpected problems in some children's experiences in the academic performance arena. These problems especially comprise of a variety of disorders which may be subclassified to attention-deficit hyperactivity disorder (ADHD), reading disability (RD), specific language impairment (SLI), speech-sound disorder (SSD), and dyspraxia. The aim of this review is to summarize the current molecular studies and some of the most exciting recent developments in molecular genetic research on LD. The findings for the association and linkage of LD with candidate genes will help to set the research agendas for future studies to follow.

Children with comorbid speech sound disorder and specific language impairment are at increased risk for attention-deficit/hyperactivity disorder

This study focuses on the comorbidity between attention-deficit/hyperactivity disorder (ADHD) symptoms and speech sound disorder (SSD). SSD is a developmental disorder characterized by speech production errors that impact intelligibility. Previous research addressing this comorbidity has typically used heterogeneous groups of speech-language disordered children. This study employed more precise speech-language diagnostic criteria and examined ADHD symptomatology in 108 SSD children between the ages of 4 and 7 years old with specific language impairment (SLI) (n = 23, 14 males, 9 females) and without SLI (n = 85, 49 males, 36 females). We also examined whether a subcategory of SSD, persistent (n = 39, 25 males, 14 females) versus normalized SSD (n = 67, 38 males, 29 females), was associated with ADHD and/or interacted with SLI to predict ADHD symptomatology. Results indicated that participants in the SSD + SLI group had higher rates of inattentive ADHD symptoms than those in the SSD-only and control groups. In addition, an unexpected interaction emerged such that children with SLI and normalized-SSD had significantly higher ADHD inattentive ratings than the other subgroups. A proposed explanation for this interaction is discussed.

Severe receptive language disorder in childhood--familial aspects and long-term outcomes: results from a Scottish study

BACKGROUND AND AIMS

Little is known about the familial characteristics of children with severe receptive specific language impairment (SLI). Affected children are more likely to have long-term problems than those with expressive SLI but to date they have only been described as small cohorts within SLI populations. We therefore aimed to describe the clinical and familial characteristics of severe receptive SLI as defined by a rigorous phenotype and to establish whether non-word repetition showed a relationship with language impairment in these families.

METHODS

Cross-sectional study of children who met ICD-10 (F80.2) criteria for receptive SLI at school entry, their siblings and genetic parents with standardised measures of language and non-verbal IQ, phonological auditory memory and speech sound inventory.

RESULTS

At a mean of 6 years after school entry with a severe receptive SLI, the 58 participants had a normal mean and standard deviation non-verbal IQ, but only 3% (two) had attained language measures in the normal range. One third still had severe receptive language impairment. One third of siblings not known to be affected had language levels outside the normal range. Phonological auditory memory was impaired in most family members.

CONCLUSION

Severe receptive SLI is nearly always associated with an equally severe reduction in expressive language skills. Language impairment in siblings may go undetected and yet they are at high risk. Family members had weak phonological auditory memory skills, suggesting that this could be a marker for language acquisition difficulties. Receptive SLI rarely resolves and trials of therapy are urgently needed.

Rearrangements of the Williams-Beuren syndrome locus: molecular basis and implications for speech and language development

The Williams-Beuren syndrome (WBS) locus on human chromosome 7q11.23 is flanked by complex chromosome-specific low-copy repeats that mediate recurrent genomic rearrangements of the region. Common genomic rearrangements arise through unequal meiotic recombination and result in complex but distinct behavioural and cognitive phenotypes. Deletion of 7q11.23 results in WBS, which is characterised by mild to moderate intellectual disability or learning difficulties, with relative cognitive strengths in verbal short-term memory and in language and extreme weakness in visuospatial construction, as well as anxiety, attention-deficit hyperactivity disorder and overfriendliness. By contrast, duplication results in severely delayed speech and expressive language, with relative strength in visuospatial construction. Although deletion and duplication of the WBS region have very different effects, both cause forms of language impairment and suggest that dosage-sensitive genes within the region are important for the proper development of human speech and language. The spectrum and frequency of genomic rearrangements at 7q11.23 presents an exceptional opportunity to identify gene(s) directly involved in human speech and language development.

Molecular Windows into Speech and Language Disorders

Why do some children fail to acquire speech and language skills despite adequate environmental input and overtly normal neurological and anatomical development? It has been suspected for several decades, based on indirect evidence, that the human genome might hold some answers to this enigma. These suspicions have recently received dramatic confirmation with the discovery of specific genetic changes which appear sufficient to derail speech and language development. Indeed, researchers are already using information from genetic studies to aid early diagnosis and to shed light on the neural pathways that are perturbed in these inherited forms of speech and language disorder. Thus, we have entered an exciting era for dissecting the neural bases of human communication, one which takes genes and molecules as a starting point. In the current article I explain how this recent paradigm shift has occurred and describe the new vistas that have opened up. I demonstrate ways of bridging the gaps between molecules, neurons and the brain, which will provide a new understanding of the aetiology of speech and language impairments.

Neuropsychology and genetics of speech, language, and literacy disorders

The authors review the neuropsychology, brain bases, and genetics of three related disorders of language development: reading disability, or developmental dyslexia (RD); language impairment (LI); and speech sound disorder (SSD). Over the past three decades, cognitive analysis has demonstrated that the reading difficulties of most children who have RD result from phonologic impairments (difficulties processing the sound structure of language). Although understanding of LI and SSD is somewhat less developed, both disorders are also associated with phonologic impairments, which may account for their comorbidity with RD. Research across levels of analysis is progressing rapidly to promote understanding not only of each disorder by itself but also of the relationships of the three disorders to each other.

Non-word repetition: an investigation of phonological complexity in children with Grammatical SLI

We investigate whether children with Grammatical Specific Language Impairment (G-SLI) are also phonologically impaired and, if so, what the nature of that impairment is. We focus on the prosodic complexity of words, based on their syllabic and metrical (stress) structure, and investigate this using a novel non-word repetition procedure, the Test of Phonological Structure (TOPhS). Participants with G-SLI (aged 12-20 years) were compared to language-matched, typically developing children (aged 4-8 years). The results reveal that, in contrast to the controls, the accuracy with which the G-SLI group repeated non-words decreased as prosodic complexity increased, even in non-words with only one- and two-syllables. The study indicates that, in G-SLI, complexity deficits in morphology and syntax can extend to prosodic phonology. The study highlights the importance of taking into account prosodic complexity in phonological assessment and the design of non-word repetition procedures.

Multivariate linkage analysis of specific language impairment (SLI)

Specific language impairment (SLI) is defined as an inability to develop appropriate language skills without explanatory medical conditions, low intelligence or lack of opportunity. Previously, a genome scan of 98 families affected by SLI was completed by the SLI Consortium, resulting in the identification of two quantitative trait loci (QTL) on chromosomes 16q (SLI1) and 19q (SLI2). This was followed by a replication of both regions in an additional 86 families. Both these studies applied linkage methods to one phenotypic trait at a time. However, investigations have suggested that simultaneous analysis of several traits may offer more power. The current study therefore applied a multivariate variance-components approach to the SLI Consortium dataset using additional phenotypic data. A multivariate genome scan was completed and supported the importance of the SLI1 and SLI2 loci, whilst highlighting a possible novel QTL on chromosome 10. Further investigation implied that the effect of SLI1 on non-word repetition was equally as strong on reading and spelling phenotypes. In contrast, SLI2 appeared to have influences on a selection of expressive and receptive language phenotypes in addition to non-word repetition, but did not show linkage to literacy phenotypes.

Heritable risk factors associated with language impairments

There is a strong genetic contribution to children’s language and literacy impairments. The aim of this study was to determine which aspects of the phenotype are familial by comparing 34 parents of probands with language/literacy impairments and 33 parents of typically developing probands. The parents responded to questionnaires regarding previous history for language/reading impairment and participated in psychometric testing. The psychometric test battery consisted of tests assessing non-verbal IQ, short-term memory, articulation, receptive grammar, reading abilities and spelling. Self-report measures demonstrated a higher prevalence of language and literacy impairments in parents of affected probands (32%) compared with parents of unaffected probands (6%). The two groups of parents differed significantly in their performance on the non-word repetition, oromotor and digit span tasks. Non-word repetition gave the best discrimination between the parent groups even when the data from the parents who actually were impaired as ascertained by direct testing or self-report were removed from the analyses. This suggests that non-word repetition serves as a marker of a family risk for language impairment. The paper concludes with a discussion of issues associated with ascertainment of specific language impairment (SLI).

Phonological short-term memory, language and literacy: developmental relationships in early adolescence in young people with SLI

BACKGROUND

Research has consistently documented a relationship between phonological short-term memory skills (STM) and specific language impairment (SLI). This study reports on the development of phonological STM abilities over 3 years in 80 young adolescents with a history of SLI, investigating the nature of the relationship between phonological STM abilities and language and literacy skills, and vice versa.

METHODS

Tests of nonverbal ability, expressive and receptive language, reading and nonword repetition were administered at 11 and 14 years of age.

RESULTS

There was striking longitudinal stability of phonological STM capacity in young people with SLI. This finding was consistent for the group as a whole, for subgroups, and at the individual level. Regression analyses revealed reciprocal relationships between phonological STM abilities and language/literacy measures. In particular, phonological STM abilities contributed significantly to later expressive language skills and basic reading skills contributed to later phonological STM abilities. Poor phonological STM abilities related to Expressive-Receptive profiles of SLI (ER-SLI) and to the presence of reading difficulties.

CONCLUSIONS

Relationships among the processes involved in language, literacy and memory in young adolescents with SLI indicate complex reciprocal interactions across development.

Differences in the nonword repetition performance of children with and without specific language impairment: a meta-analysis

PURPOSE

This study presents a meta-analysis of the difference in nonword repetition performance between children with and without specific language impairment (SLI). The authors investigated variability in the effect sizes (i.e., the magnitude of the difference between children with and without SLI) across studies and its relation to several factors: type of nonword repetition task, age of SLI sample, and nonword length.

METHOD

The authors searched computerized databases and reference sections and requested unpublished data to find reports of nonword repetition tasks comparing children with and without SLI.

RESULTS

Children with SLI exhibited very large impairments in nonword repetition, performing an average (across 23 studies) of 1.27 standard deviations below children without SLI. A moderator analysis revealed that different versions of the nonword repetition task yielded significantly different effect sizes, indicating that the measures are not interchangeable. The second moderator analysis found no association between effect size and the age of children with SLI. Finally, an exploratory meta-analysis found that children with SLI displayed difficulty repeating even short nonwords, with greater difficulty for long nonwords.

CONCLUSIONS

These findings have potential to affect how nonword repetition tasks are used and interpreted, and suggest several directions for future research.

Genetic studies of stuttering in a founder population

Genome-wide linkage and association analyses were conducted to identify genetic determinants of stuttering in a founder population in which 48 individuals affected with stuttering are connected in a single 232-person genealogy. A novel approach was devised to account for all necessary relationships to enable multipoint linkage analysis. Regions with nominal evidence for linkage were found on chromosomes 3 (P=0.013, 208.8 centiMorgans (cM)), 13 (P=0.012, 52.6 cM), and 15 (P=0.02, 100 cM). Regions with nominal evidence for association with stuttering that overlapped with a linkage signal are located on chromosomes 3 (P=0.0047, 195 cM), 9 (P=0.0067, 46.5 cM), and 13 (P=0.0055, 52.6 cM). We also conducted the first meta-analysis for stuttering using results from linkage studies in the Hutterites and The Illinois International Genetics of Stuttering Project and identified regions with nominal evidence for linkage on chromosomes 2 (P=0.013, 180-195 cM) and 5 (P=0.0051, 105-120 cM; P=0.015, 120-135 cM). None of the linkage signals detected in the Hutterite sample alone, or in the meta-analysis, meet genome-wide criteria for significance, although some of the stronger signals overlap linkage mapping signals previously reported for other speech and language disorders.

EDUCATIONAL OBJECTIVES

After reading this article, the reader will be able to: (1) summarize information about the background of common disorders and methodology of genetic studies; (2) evaluate the role of genetics in stuttering; (3) discuss the value of using founder populations in genetic studies; (4) articulate the importance of combining several studies in a meta-analysis; (5) discuss the overlap of genetic signals identified in stuttering with other speech and language disorders.

Genes, language development, and language disorders

Genetic factors are important contributors to language and learning disorders, and discovery of the underlying genes can help delineate the basic neurological pathways that are involved. This information, in turn, can help define disorders and their perceptual and processing deficits. Initial molecular genetic studies of dyslexia, for example, appear to converge on defects in neuronal and axonal migration. Further study of individuals with abnormalities of these genes may lead to the recognition of characteristic cognitive deficits attributable to the neurological dysfunction. Such abnormalities may affect other disorders as well, and studies of co-morbidity of dyslexia with attention deficit disorder and speech sound disorder are helping to define the scope of these genes and show the etiological and cognitive commonalities between these conditions. The genetic contributions to specific language impairment (SLI) are not as well defined at this time, but similar molecular approaches are being applied to identify genes that influence SLI and comorbid disorders. While there is co-morbidity of SLI with dyslexia, it appears that most of the common genetic effects may be with the language characteristics of autism spectrum disorders rather than with dyslexia and related disorders. Identification of these genes and their neurological and cognitive effects should lay out a functional network of interacting genes and pathways that subserve language development. Understanding these processes can form the basis for refined procedures for diagnosis and treatment.

The Neural Basis of Language Development and Its Impairment

The neural correlates of early language development and language impairment are described, with the adult language-related brain systems as a target model. Electrophysiological and hemodynamic studies indicate that language functions to be installed in the child's brain are similar to those of adults, with lateralization being present at birth, phonological processes during the first months, semantic processes at 12 months, and syntactic processes around 30 months. These findings support the view that the brain basis of language develops continuously over time. Discontinuities are observed in children with language impairment. Here, the observed functional abnormalities are accompanied by structural abnormalities in inferior frontal and temporal brain regions.

The genetic bases of speech sound disorders: evidence from spoken and written language

The purpose of this article is to review recent findings suggesting a genetic susceptibility for speech sound disorders (SSD), the most prevalent communication disorder in early childhood. The importance of genetic studies of SSD and the hypothetical underpinnings of these genetic findings are reviewed, as well as genetic associations of SSD with other language and reading disabilities. The authors propose that many genes contribute to SSD. They further hypothesize that some genes contribute to SSD disorders alone, whereas other genes influence both SSD and other written and spoken language disorders. The authors postulate that underlying common cognitive traits, or endophenotypes, are responsible for shared genetic influences of spoken and written language. They review findings from their genetic linkage study and from the literature to illustrate recent developments in this area. Finally, they discuss challenges for identifying genetic influence on SSD and propose a conceptual framework for study of the genetic basis of SSD.

Short-term and working memory in specific language impairment

BACKGROUND

Investigations of the cognitive processes underlying specific language impairment (SLI) have implicated deficits in the storage and processing of phonological information, but to date these abilities have not been studied in the same group of children with SLI.

AIMS

To examine the extent to which deficits in immediate verbal short-term and working memory may co-occur in a group of children with SLI.

METHODS & PROCEDURES

Twenty children aged 7-11 years with SLI completed a comprehensive battery of short-term and working memory, as well as two phonological awareness tasks.

OUTCOMES & RESULTS

The majority of the group had deficits in both verbal short-term and working memory, which persisted after the general language abilities of the children were taken into account. A substantial minority showed deficits on visuospatial short-term memory, while impairments of phonological awareness were less marked.

CONCLUSIONS

The data indicate dual deficits in verbal short-term and working memory that exceed criterial language abilities characteristic of SLI and may plausibly underpin some of the language learning difficulties experienced by these children.

Nonword repetition: a comparison of tests

PURPOSE

This study compared performance of children on 2 tests of nonword repetition to investigate the factors that may contribute to the well-documented nonword repetition deficit in specific language impairment (SLI).

METHOD

Twelve children with SLI age 7 to 11 years, 12 age-matched control children, and 12 control children matched for language ability completed 2 tests of nonword repetition: the Children's Test of Nonword Repetition (CNRep) and the Nonword Repetition Test (NRT).

RESULTS

The children with SLI performed significantly more poorly on both tests than typically developing children of the same age. The SLI group was impaired on the CNRep but not the NRT relative to younger children with similar language abilities when adjustments were made for differences in general cognitive ability. The children with SLI repeated the lengthiest nonwords and the nonwords containing consonant clusters significantly less accurately than the control groups.

CONCLUSION

The evidence suggests that the nonword repetition deficit in SLI may arise from a number of factors, including verbal short-term memory, lexical knowledge, and output processes.

Early N400 development and later language acquisition

Recent developmental research on word processing has shown that mechanisms of lexical priming are already present in 12-month-olds whereas mechanisms of semantic integration indexed by the N400 mature a few months later. In a longitudinal setting we investigated whether the occurrence of an N400 at 19 months is associated with the children's language skills later on. To this end children were retrospectively grouped according to their verbal performance in a language test at 30 months. Children with later age-adequate expressive language skills already displayed an N400 at 19 months. In contrast, children with later poor expressive language skills who have an enhanced risk for the development of specific language impairment (SLI) did not show an early N400. The results imply that children who have deficits in their expressive language at the age of 30 months are already impaired in their semantic development about one year earlier.

The jewels of our genome: the search for the genomic changes underlying the evolutionarily unique capacities of the human brain

The recent publication of the initial sequence and analysis of the chimp genome allows us, for the first time, to compare our genome with that of our closest living evolutionary relative. With more primate genome sequences being pursued, and with other genome-wide, cross-species comparative techniques emerging, we are entering an era in which we will be able to carry out genomic comparisons of unprecedented scope and detail. These studies should yield a bounty of new insights about the genes and genomic features that are unique to our species as well as those that are unique to other primate lineages, and may begin to causally link some of these to lineage-specific phenotypic characteristics. The most intriguing potential of these new approaches will be in the area of evolutionary neurogenomics and in the possibility that the key human lineage–specific (HLS) genomic changes that underlie the evolution of the human brain will be identified. Such new knowledge should provide fresh insights into neuronal development and higher cognitive function and dysfunction, and may possibly uncover biological mechanisms for information storage, analysis, and retrieval never previously seen.

“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.

Developmental cognitive genetics: how psychology can inform genetics and vice versa

Developmental neuropsychology is concerned with uncovering the underlying basis of developmental disorders such as specific language impairment (SLI), developmental dyslexia, and autistic disorder. Twin and family studies indicate that genetic influences play an important part in the aetiology of all of these disorders, yet progress in identifying genes has been slow. One way forward is to cut loose from conventional clinical criteria for diagnosing disorders and to focus instead on measures of underlying cognitive mechanisms. Psychology can inform genetics by clarifying what the key dimensions are for heritable phenotypes. However, it is not a one-way street. By using genetically informative designs, one can gain insights about causal relationships between different cognitive deficits. For instance, it has been suggested that low-level auditory deficits cause phonological problems in SLI. However, a twin study showed that, although both types of deficit occur in SLI, they have quite different origins, with environmental factors more important for auditory deficit, and genes more important for deficient phonological short-term memory. Another study found that morphosyntactic deficits in SLI are also highly heritable, but have different genetic origins from impairments of phonological short-term memory. A genetic perspective shows that a search for the underlying cause of developmental disorders may be misguided, because they are complex and heterogeneous and are associated with multiple risk factors that only cause serious disability when they occur in combination.

Speech sound disorder influenced by a locus in 15q14 region

Despite a growing body of evidence indicating that speech sound disorder (SSD) has an underlying genetic etiology, researchers have not yet identified specific genes predisposing to this condition. The speech and language deficits associated with SSD are shared with several other disorders, including dyslexia, autism, Prader-Willi Syndrome (PWS), and Angelman's Syndrome (AS), raising the possibility of gene sharing. Furthermore, we previously demonstrated that dyslexia and SSD share genetic susceptibility loci. The present study assesses the hypothesis that SSD also shares susceptibility loci with autism and PWS. To test this hypothesis, we examined linkage between SSD phenotypes and microsatellite markers on the chromosome 15q14-21 region, which has been associated with autism, PWS/AS, and dyslexia. Using SSD as the phenotype, we replicated linkage to the 15q14 region (P=0.004). Further modeling revealed that this locus influenced oral-motor function, articulation and phonological memory, and that linkage at D15S118 was potentially influenced by a parent-of-origin effect (LOD score increase from 0.97 to 2.17, P=0.0633). These results suggest shared genetic determinants in this chromosomal region for SSD, autism, and PWS/AS.

Distinct genetic influences on grammar and phonological short-term memory deficits: evidence from 6-year-old twins

Children with language impairments have limitations of phonological short-term memory (STM) and have distinctive problems with certain aspects of grammar. Both deficits have been proposed as phenotypic markers of heritable language impairment. We studied 173 twin pairs, selected to be over-representative of children with risk of developmental language impairment, using a battery of standardized language and intelligence tests, a test of nonword repetition to index phonological STM and two elicitation tasks to assess use of verb tense marking. As predicted, the phonological STM and the verb tense measures both discriminated children with risk of language impairment from low risk children, and DeFries-Fulker analysis showed that impairments on both tasks were significantly heritable. However, there was minimal phenotypic and etiological overlap between the two deficits, suggesting that different genes are implicated in causing these two kinds of language difficulty. From an evolutionary perspective, these data are consistent with the view that language is a complex function that depends on multiple underlying skills with distinct genetic origins.

Quantitative trait locus analysis of nonverbal communication in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental syndrome marked by impairments in social interactive functioning and communication skills, and the presence of repetitive and restrictive behaviors. Twin and linkage studies provide evidence that ASD is heritable and genetically complex. Genetic analyses of familial quantitative traits in those with ASD may help to reveal underlying risk genes. We report a quantitative trait locus (QTL) analysis of nonverbal communication (NVC) in 228 families from the autism genetics resource exchange (AGRE) ascertained for at least two siblings with ASD. QTL at 1p13-q12, 4q21-25, 7q35, 8q23-24, and 16p12-13 indicate that genes at these loci may contribute to the variation in NVC among those with ASD. Using the criteria of Lander and Kruglyak, the QTL at 1p13-q12 is 'suggestive', while the other four are 'possible'. To assess whether these QTL are likely to harbor genes contributing specifically to the deficits in NVC, linkage analysis of ASD sibships with the most severe NVC scores was conducted. The sibships were identified by ordered-subset analyses (OSA), and families with the most severe NVC scores displayed lod scores of 3.4 at 8q23-24 and 3.8 at 16p12-13, indicating that these two regions are likely to harbor gene(s) contributing to ASD by predisposing to deficits in NVC.

Practitioner review: short-term and working memory impairments in neurodevelopmental disorders: diagnosis and remedial support

BACKGROUND

This article provides an introduction to current models of working and short-term memory, their links with learning, and diagnosis of impairments. The memory impairments associated with a range of neurodevelopmental disorders (Down's syndrome, Williams syndrome, Specific Language Impairment, and attentional deficits) are discussed.

METHODS

Methods of alleviating the adverse consequences of working and short-term memory impairments for learning are identified.

CONCLUSION

Impairments of short-term and working memory are associated with learning difficulties that can be substantial, and that can be minimised by appropriate methods of remedial support.

Linkage of speech sound disorder to reading disability loci

BACKGROUND

Speech sound disorder (SSD) is a common childhood disorder characterized by developmentally inappropriate errors in speech production that greatly reduce intelligibility. SSD has been found to be associated with later reading disability (RD), and there is also evidence for both a cognitive and etiological overlap between the two disorders. The present study tested whether SSD is linked to replicated risk loci for RD.

METHOD

One hundred and eleven probands with SSD and their 76 siblings were tested with measures of speech, phonological memory (Nonword Repetition-NWR), and phonological awareness and genotyped for linkage markers on chromosomes 1p36, 6p22, and 15q21. Both single point and multipoint linkage were tested with multiple methods.

RESULTS

The speech and NWR phenotypes were linked to the RD loci on chromosomes 6 and 15, with suggestive results for the RD locus on chromosome 1.

CONCLUSIONS

It now appears that several RD loci are pleiotropic for SSD, extending the findings of Stein et al. (2004) for the RD locus on Chromosome 3.

Genetic influences on language impairment and phonological short-term memory

It has been known for some years that specific language impairment (SLI), an unexpected failure to acquire age-appropriate language skills, is highly heritable. However, molecular genetic studies have been hampered by the heterogeneity of the disorder and the predominant lack of clear genotype-phenotype relationships. We review recent studies suggesting that a better understanding of the genetics of SLI might emerge if we move away from clinical criteria for diagnosis to look instead at a theoretically based quantitative and cognitive measure of the phenotype: a test of phonological short-term memory (STM). Deficient phonological STM has been linked to specific genetic loci, and might play a role in determining some types of reading impairment as well as SLI. Identifying those cognitive deficits that work best as indices of heritable phenotypes will help us to uncover the aetiology of developmental disorders.

Quantitative genome scan and Ordered-Subsets Analysis of autism endophenotypes support language QTLs

Autism is a neurodevelopmental syndrome with early childhood onset and deficits in three behavioral and cognitive dimensions: language, social skills and repetitive or restrictive behaviors. We hypothesized that using these endophenotypes would provide more power to detect linkage than the diagnosis of autism. Previously, we reported results for a nonparametric quantitative trait locus (QTL) genome scan in 152 families with autism, which revealed a linkage peak related to spoken language on 7q35. Here, we present the results of a nonparametric QTL scan of autism endophenotypes in 291 multiplex families, including the original 152. The strongest evidence for an 'age at first word' QTL was on chromosomes 3q at 147 cM (Z=3.10, P<0.001), and 17q at 93 cM (Z=2.84, P=0.002), both represent novel susceptibility loci for autism endophenotypes. There was also support for a previously identified autism peak on chromosome 17 at 43 cM (Z=2.22, P=0.013) with 'age at first phrase'. The 7q35 language peak was attenuated (Z=2.05, P=0.02) compared with the original finding. To explore the possibility of increased heterogeneity resulting from the addition of 135 families to the sample, we conducted an Ordered-Subsets Analysis on chromosome 7; these results suggest that the 132 autism families with the earliest average age at first word are responsible for the QTL on 7q35. This locus on 7q35 may harbor a gene contributing variability in spoken language that is not uniquely related to language delay in autism.

Toward diagnostic and phenotype markers for genetically transmitted speech delay

Converging evidence supports the hypothesis that the most common subtype of childhood speech sound disorder (SSD) of currently unknown origin is genetically transmitted. We report the first findings toward a set of diagnostic markers to differentiate this proposed etiological subtype (provisionally termed speech delay-genetic) from other proposed subtypes of SSD of unknown origin. Conversational speech samples from 72 preschool children with speech delay of unknown origin from 3 research centers were selected from an audio archive. Participants differed on the number of biological, nuclear family members (0 or 2+) classified as positive for current and/or prior speech-language disorder. Although participants in the 2 groups were found to have similar speech competence, as indexed by their Percentage of Consonants Correct scores, their speech error patterns differed significantly in 3 ways. Compared with children who may have reduced genetic load for speech delay (no affected nuclear family members), children with possibly higher genetic load (2+ affected members) had (a) a significantly higher proportion of relative omission errors on the Late-8 consonants; (b) a significantly lower proportion of relative distortion errors on these consonants, particularly on the sibilant fricatives /s/, /z/, and //; and (c) a significantly lower proportion of backed /s/ distortions, as assessed by both perceptual and acoustic methods. Machine learning routines identified a 3-part classification rule that included differential weightings of these variables. The classification rule had diagnostic accuracy value of 0.83 (95% confidence limits = 0.74-0.92), with positive and negative likelihood ratios of 9.6 (95% confidence limits = 3.1-29.9) and 0.40 (95% confidence limits = 0.24-0.68), respectively. The diagnostic accuracy findings are viewed as promising. The error pattern for this proposed subtype of SSD is viewed as consistent with the cognitive-linguistic processing deficits that have been reported for genetically transmitted verbal disorders.

Multilingual home environment and specific language impairment: a case-control study in Chinese children

Specific language impairment (SLI) is a common developmental disorder in young children. To investigate the association between multilingual home environment and SLI, we conducted a case-control study in Hong Kong Chinese children over a 4-year period in the Duchess of Kent Children's Hospital. Consecutive medical records of all new referrals below 5 years of age were reviewed and children diagnosed with SLI (case) were compared with those referred with other developmental and behavioural problems who had been assessed as having normal language and overall development (control) using the Griffiths Mental Developmental Scale. SLI was defined as those with a language quotient more than one standard deviation below the mean and below the general developmental quotient in children with normal general developmental quotient, but without neurological or other organic diseases. We used binary and ordinal logistic regression to assess any association between SLI and multilingual exposure at home, adjusting for age and gender of subjects, parental age, education level and occupational status, number of siblings, family history of language delay and main caregiver at home. Multivariable linear regression was used to examine the effect of covariates on the language comprehension and expression standard scores assessed by the Reynell Developmental Language Scale. A total of 326 cases and 304 controls were included. The mean ages of cases and controls were 2.56 and 2.89 years respectively. Boys predominated in both groups (cases, 75.2%; controls, 60.2%). The children were exposed to between one and four languages at home, the major ones being Cantonese Chinese followed by English. The adjusted odds ratio (OR) of SLI was 2.94; [95% confidence interval (CI) 1.82, 4.74] for multilingual compared with monolingual exposure. A significant linear dose-response relationship was found (OR of SLI = 2.58 [1.72, 3.88] for each additional language to which the child was exposed). Male gender (OR = 1.88 [1.24, 2.87]), positive family history (OR = 2.01 [1.17, 3.47]), lower education levels of parents (P = 0.028 for father, P = 0.038 for mother) and lower occupational status of father (P = 0.005) were also risk factors for SLI. Multilingual exposure also significantly reduced the language quotient (P = 0.012) and language comprehension standard score (P = 0.016) of children with SLI, but not of normal children. We concluded that multilingual home environment is associated with SLI with a dose-response relationship. Exposure to multiple languages might adversely affect subsequent language ability.

Genetic influences on specific versus nonspecific language impairment in 4-year-old twins

The present study addresses the distinction between specific (SLI) and nonspecific (NLI) language impairment at an etiological level by estimating the relative genetic and environmental contributions to language impairment in children with SLI and NLI. Drawing on a large longitudinal twin study, we tested a sample of 356 four-and-a-half-year-old children with low language ability and their twin partners at home on a range of language and nonverbal measures. For children whose language and nonverbal abilities were both low (NLI), genetic influence on language impairment was moderate and shared environmental influence was substantial. A similar pattern emerged for children whose language difficulties occurred in apparent isolation (SLI), although there was a trend for the genetic effects to be smaller for SLI than for NLI: Group heritability was .18 for SLI and .52 for NLI. Probandwise cross-concordances were suggestive of some genetic overlap between these two groups, but not with a subgroup of children with more severe cognitive delay.

Genetic Influences in Different Aspects of Language Development: The Etiology of Language Skills in 4.5-Year-Old Twins

The genetic and environmental etiologies of diverse aspects of language ability and disability, including articulation, phonology, grammar, vocabulary, and verbal memory, were investigated in a U.K. sample of 787 pairs of 4.5-year-old same-sex and opposite-sex twins. Moderate genetic influence was found for all aspects of language in the normal range. A similar pattern was found at the low end of the distribution with the exception of two receptive measures. Environmental influence was mainly due to nonshared factors, unique to the individual, with little influence from shared environment for most measures. Genetic and environmental influences on language ability and disability are quantitatively and qualitatively similar for males and females.

The faculty of language: what's special about it?

We examine the question of which aspects of language are uniquely human and uniquely linguistic in light of recent suggestions by Hauser, Chomsky, and Fitch that the only such aspect is syntactic recursion, the rest of language being either specific to humans but not to language (e.g. words and concepts) or not specific to humans (e.g. speech perception). We find the hypothesis problematic. It ignores the many aspects of grammar that are not recursive, such as phonology, morphology, case, agreement, and many properties of words. It is inconsistent with the anatomy and neural control of the human vocal tract. And it is weakened by experiments suggesting that speech perception cannot be reduced to primate audition, that word learning cannot be reduced to fact learning, and that at least one gene involved in speech and language was evolutionarily selected in the human lineage but is not specific to recursion. The recursion-only claim, we suggest, is motivated by Chomsky's recent approach to syntax, the Minimalist Program, which de-emphasizes the same aspects of language. The approach, however, is sufficiently problematic that it cannot be used to support claims about evolution. We contest related arguments that language is not an adaptation, namely that it is "perfect," non-redundant, unusable in any partial form, and badly designed for communication. The hypothesis that language is a complex adaptation for communication which evolved piecemeal avoids all these problems.

Differentiating SLI from ADHD using children's sentence recall and production of past tense morphology

Measures of sentence recall and past tense marking were used to examine the similarities and differences between children with Attention Deficit/Hyperactivity Disorder (ADHD), children with specific language impairment (SLI), and typically developing (TD) children. Both SLI and ADHD group means for sentence recall tasks were significantly lower than the TD control group (SLI<ADHD<TD). In contrast, limitations in past tense marking were characteristic of the SLI group (SLI<ADHD=TD). Frequent affix omissions or bare stem errors (e.g. the girl colour the picture; the girl fall in the net) differentiated the SLI group from the other two groups. Over-regularization errors (e.g. the girl falled into the net) did not (SLI=ADHD=TD). Clinical implications are discussed.

Domain-specific cognitive systems: insight from Grammatical-SLI

Specific language-impairment (SLI) is a disorder of language acquisition in children who otherwise appear to be normally developing. Controversy surrounds whether SLI results from impairment to a "domain-specific" system devoted to language itself or from some more "domain-general" system. I compare these two views of SLI, and focus on three components of grammar that are good candidates for domain-specificity: syntax, morphology and phonology. I argue that the disorder is heterogeneous, and that deficits of different subgroups potentially stem from different underlying causes. Interestingly, although poor sensory or non-verbal abilities often co-occur with SLI, there is no evidence that these impairments cause the grammatical deficits found in SLI. Moreover, evidence suggests that impairment in at least one subgroup is specific to grammar.

Generalist Genes and Learning Disabilities

The authors reviewed recent quantitative genetic research on learning disabilities that led to the conclusion that genetic diagnoses differ from traditional diagnoses in that the effects of relevant genes are largely general rather than specific. This research suggests that most genes associated with common learning disabilities--language impairment, reading disability, and mathematics disability--are generalists in 3 ways. First, genes that affect common learning disabilities are largely the same genes responsible for normal variation in learning abilities. Second, genes that affect any aspect of a learning disability affect other aspects of the disability. Third, genes that affect one learning disability are also likely to affect other learning disabilities. These quantitative genetic findings have far-reaching implications for molecular genetics and neuroscience as well as psychology.

The search for autism disease genes

Autism is a heritable disorder characterized by phenotypic and genetic complexity. This review begins by surveying current linkage, gene association, and cytogenetic studies performed with the goal of identifying autism disease susceptibility variants. Though numerous linkages and associations have been identified, they tend to diminish upon closer examination or attempted replication. The review therefore explores challenges to current methodologies presented by the complexities of autism that might underlie some of the current difficulties, and finishes by describing emerging phenotypic, statistical, and molecular investigational approaches that offer hope of overcoming those challenges.

Family-based association study of DYX1C1 variants in autism

DYX1C1: was recently identified as a candidate gene for developmental dyslexia, which is characterized by an unexpected difficulty in learning to read and write despite adequate intelligence, motivation, and education. It will be important to clarify, whether the phenotype caused by DYX1C1 extends to other language-related or comorbid disorders. Impaired language development is one of the essential features in autism. Therefore, we analyzed the allelic distribution of the DYX1C1 gene by family-based association method in 100 Finnish autism families. No evidence for association was observed with any intragenic marker or with haplotypes constructed from alleles of several adjacent markers. No evidence for deviated allelic diversity was either observed: the frequency of expected dyslexia risk haplotype was comparable to its frequency in Finnish controls. Thus it seems unlikely that DYX1C1 gene would be involved in the genetic etiology of autism in Finnish patients.

Genetic components of vocal learning

Vocal learning is a rare trait. Humans depend on vocal learning to acquire spoken language, but most species that communicate acoustically have an innate repertoire of sounds that they use for information exchange. Among the few non-human species that also rely on vocal learning, songbirds have provided by far the most information for understanding this process. This article concentrates on the genetic components of vocal learning in humans and birds. We summarize the existing evidence for a genetic predisposition towards acquiring the species-specific human and avian vocal repertoires. We describe the approaches used for finding genes involved in shaping the neural circuitry required for vocal learning or in mediating the learning process itself. Special attention is given to a particular gene, FOXP2, which has been implicated in a human speech and language disorder. We have studied FoxP2 in avian vocal learners and non-learners and review evidence that links both the molecule and its close homologue FoxP1 to the development of brain regions implicated in vocal learning and to their function. FoxP2 has a characteristic expression pattern in a brain structure uniquely associated with learned vocal communication, Area X in songbirds, or its analogue in parrots and hummingbirds. In both avian song learners and non-learners FoxP2 expression predominates in sensory and sensory-motor circuits. These latter regions also express FoxP2 in mammals and reptiles. We conclude that FoxP2 is important for the building and function of brain pathways including, but not limited to, those essential for learned vocal communication.

Lineage-specific gene duplication and loss in human and great ape evolution

Given that gene duplication is a major driving force of evolutionary change and the key mechanism underlying the emergence of new genes and biological processes, this study sought to use a novel genome-wide approach to identify genes that have undergone lineage-specific duplications or contractions among several hominoid lineages. Interspecies cDNA array-based comparative genomic hybridization was used to individually compare copy number variation for 39,711 cDNAs, representing 29,619 human genes, across five hominoid species, including human. We identified 1,005 genes, either as isolated genes or in clusters positionally biased toward rearrangement-prone genomic regions, that produced relative hybridization signals unique to one or more of the hominoid lineages. Measured as a function of the evolutionary age of each lineage, genes showing copy number expansions were most pronounced in human (134) and include a number of genes thought to be involved in the structure and function of the brain. This work represents, to our knowledge, the first genome-wide gene-based survey of gene duplication across hominoid species. The genes identified here likely represent a significant majority of the major gene copy number changes that have occurred over the past 15 million years of human and great ape evolution and are likely to underlie some of the key phenotypic characteristics that distinguish these species.

This genome-wide analysis reports the major lineage-specific gene copy number changes that have occurred over the past 15 million years of human and great ape evolution

Are phonological processing deficits part of the broad autism phenotype?

Two tests of phonological processing, nonword repetition, and nonsense passage reading, were administered to 80 probands with autistic disorder or PDDNOS (index cases) and 59 typically developing controls, together with their parents and siblings. In addition, parents completed a questionnaire about history of language and literacy problems, and all participants were given tests of verbal (VIQ) and performance IQ (PIQ). Parents also completed the Autism-Spectrum Quotient, which was used to index the broad autism phenotype. Index probands scored well below control probands on the two phonological tests. However, on neither phonological measure did index relatives differ from control relatives. Within the index group, there was no relationship between the proband's level of VIQ, or age at achieving phrase speech, and phonological score of relatives. VIQ was the only measure to show any familiality within the index group. Reported history of language and literacy problems did not differentiate index parents from control parents overall, but those who were categorized as cases of the broad phenotype reported more history of language and literacy problems than did other index parents. However, they did not have poorer scores on the phonological measures. It is concluded that phonological processing deficits are not part of the broad autism phenotype.

Neurobiology of specific language impairment

This review summarizes what is known about the neurobiology of specific language impairment. Despite its name, specific language impairment is frequently not specific. It is common to find associated impairments in motor skills, cognitive function, attention, and reading in children who meet criteria for specific language impairment. There is evidence that limitation in phonologic working memory may be a core deficit in specific language impairment. Both genetic and environmental factors have been shown to be important etiologic factors in specific language impairment. Structural neuroimaging studies suggest that atypical patterns of asymmetry of language cortex, white-matter abnormalities, and cortical dysplasia may be associated with specific language impairment. Abnormalities in the later stages of auditory processing have been demonstrated using auditory event-related potentials. Functional neuroimaging may cast further light on the neurobiology of specific language impairment and serve as a means of developing and evaluating therapy. A better understanding of the neurobiology of specific language impairment is critical for the rational development of therapeutic strategies to treat this common disorder.

Highly significant linkage to the SLI1 locus in an expanded sample of individuals affected by specific language impairment

Specific language impairment (SLI) is defined as an unexplained failure to acquire normal language skills despite adequate intelligence and opportunity. We have reported elsewhere a full-genome scan in 98 nuclear families affected by this disorder, with the use of three quantitative traits of language ability (the expressive and receptive tests of the Clinical Evaluation of Language Fundamentals and a test of nonsense word repetition). This screen implicated two quantitative trait loci, one on chromosome 16q (SLI1) and a second on chromosome 19q (SLI2). However, a second independent genome screen performed by another group, with the use of parametric linkage analyses in extended pedigrees, found little evidence for the involvement of either of these regions in SLI. To investigate these loci further, we have collected a second sample, consisting of 86 families (367 individuals, 174 independent sib pairs), all with probands whose language skills are >/=1.5 SD below the mean for their age. Haseman-Elston linkage analysis resulted in a maximum LOD score (MLS) of 2.84 on chromosome 16 and an MLS of 2.31 on chromosome 19, both of which represent significant linkage at the 2% level. Amalgamation of the wave 2 sample with the cohort used for the genome screen generated a total of 184 families (840 individuals, 393 independent sib pairs). Analysis of linkage within this pooled group strengthened the evidence for linkage at SLI1 and yielded a highly significant LOD score (MLS = 7.46, interval empirical P<.0004). Furthermore, linkage at the same locus was also demonstrated to three reading-related measures (basic reading [MLS = 1.49], spelling [MLS = 2.67], and reading comprehension [MLS = 1.99] subtests of the Wechsler Objectives Reading Dimensions).

Psychopathology in the postgenomic era

We are rapidly approaching the postgenomic era in which we will know all of the 3 billion DNA bases in the human genome sequence and all of the variations in the genome sequence that are ultimately responsible for genetic influence on behavior. These ongoing advances and new techniques will make it easier to identify genes associated with psychopathology. Progress in identifying such genes has been slower than some experts expected, probably because many genes are involved for each phenotype, which means the effect of any one gene is small. Nonetheless, replicated linkages and associations are being found, for example, for dementia, reading disability, and hyperactivity. The future of genetic research lies in finding out how genes work (functional genomics). It is important for the future of psychology that pathways between genes and behavior be examined at the top-down psychological level of analysis (behavioral genomics), as well as at the bottom-up molecular biological level of cells or the neuroscience level of the brain. DNA will revolutionize psychological research and treatment during the coming decades.

Pleiotropic effects of a chromosome 3 locus on speech-sound disorder and reading

Speech-sound disorder (SSD) is a complex behavioral disorder characterized by speech-sound production errors associated with deficits in articulation, phonological processes, and cognitive linguistic processes. SSD is prevalent in childhood and is comorbid with disorders of language, spelling, and reading disability, or dyslexia. Previous research suggests that developmental problems in domains associated with speech and language acquisition place a child at risk for dyslexia. Recent genetic studies have identified several candidate regions for dyslexia, including one on chromosome 3 segregating in a large Finnish pedigree. To explore common genetic influences on SSD and reading, we examined linkage for several quantitative traits to markers in the pericentrometric region of chromosome 3 in 77 families ascertained through a child with SSD. The quantitative scores measured several processes underlying speech-sound production, including phonological memory, phonological representation, articulation, receptive and expressive vocabulary, and reading decoding and comprehension skills. Model-free linkage analysis was followed by identification of sib pairs with linkage and construction of core shared haplotypes. In our multipoint analyses, measures of phonological memory demonstrated the strongest linkage (marker D3S2465, P=5.6 x 10(-5), and marker D3S3716, P=6.8 x 10(-4)). Tests for single-word decoding also demonstrated linkage (real word reading: marker D3S2465, P=.004; nonsense word reading: marker D3S1595, P=.005). The minimum shared haplotype in sib pairs with similar trait values spans 4.9 cM and is bounded by markers D3S3049 and D3S3045. Our results suggest that domains common to SSD and dyslexia are pleiotropically influenced by a putative quantitative trait locus on chromosome 3.