Developmental Language Disorder

Developmental Language Disorders

Professor Courtenay Norbury
Professor Courtenay Norbury

Courtenay Norbury is Professor of Developmental Disorders of Language and Communication at Psychology and Language Sciences, University College London. She is the Director of the Literacy, Language and Communication (LiLaC) Lab and a Fellow of the Royal College of Speech and Language Therapists.

She obtained her PhD in Experimental Psychology at the University of Oxford, working with Professor Dorothy Bishop on the overlapping language profiles that characterise autism spectrum disorder and ‘specific’ language impairment. Professor Norbury’s current research focuses on language disorders and how language interacts with other aspects of development. She is leading SCALES, a population study of language development and disorder from school entry. She is also a founding member of the RADLD campaign.

Developmental language disorders (DLD)

Developmental language disorder (DLD) is diagnosed when a child’s language skills are persistently below the level expected for the child’s age. In DLD, language deficits occur in the absence of a known biomedical condition, such as autism spectrum disorder or Down syndrome, and interfere with the child’s ability to communicate effectively with other people. Expressive language is characterised by non-specific words and short simple sentences to express meanings beyond the age at which children may be using more complex language. For example, when typical children can say ‘that boy cuts shapes out paper with sharp scissors’, the child with DLD might say ‘him doing cuts’ to express the same idea. Though such limitations of expressive language are readily apparent, for many children, understanding of language (receptive language) is also a challenge. Language disorders emerge in early childhood, have a significant impact on everyday social interactions or educational progress, and persist throughout the school years and into adulthood.

  • Aspects of language may be variably impaired and include:
  • Phonology (speech sounds)
  • Semantics (vocabulary)
  • Syntax (grammar) and morphology (endings on words that express grammatical relationships, like past tense –ed in English)
  • Discourse (narrative, conversation)
  • Pragmatics (social communication, inferencing, figurative language)

The exact cause of DLD is not known, but it is likely that there are several interacting genetic and environmental factors, rather than one single identifiable cause.

Behavioural interventions are the most common approach to treating DLD. Such interventions are typically carried out by speech-language therapists, though in some instances therapy may be delivered by parents or education staff under the supervision of the speech-language therapist. These interventions can significantly enhance a child’s ability to communicate and can increase competence in specific areas of language, but, as yet, there is no cure for DLD.

  • Introduction

    The terminology for children’s language problems has been extremely variable and confusing, with many different labels being used by different professional groups (D. V. M. Bishop, 2017). In the UK, education services include DLD under the umbrella term SLCN, or speech, language and communication needs. In research, ‘specific language impairment’ or SLI was the term most commonly used, but there has been growing recognition that language is rarely selectively impaired and considerable controversy about the use of non-verbal IQ scores in diagnosis and treatment decisions. For example, children with non-verbal IQ scores below 85 are frequently excluded from research studies (Reilly et al., 2014) and denied access to specialist clinical services (Dockrell, Lindsay, Letchford, & Mackie, 2006).

    The lack of consistency in terminology has been directly linked to poor public awareness of DLD (D.V.M. Bishop, 2010). To address this issue, the CATALISE consortium recently undertook a Delphi exercise to achieve consensus on diagnostic terms and criteria (D. V. M. Bishop, Snowling, Thompson, Greenhalgh, & and the, 2017). This cross-disciplinary panel of experts recommended the term Developmental Language Disorder, to denote a problem with language that stems from atypical developmental processes (as opposed to acquired brain damage, as in stroke or head injury) and to convey the serious nature and potential long term consequences of language deficits. DLD includes SLI, but allows for more variable non-verbal cognitive abilities. Including ‘disorder’ in the diagnostic label also provides consistency with other neurodevelopmental conditions such as ‘autism spectrum disorder’ or ‘attention deficit hyperactivity disorder’.

    Language is a multi-faceted system and it is likely that children will show variable patterns of skill and deficit. Efforts to identify sub-types of language disorder have generally not been successful and many large scale studies report that assessments of different language domains tend to load on a common language factor (Tomblin & Zhang, 2006). The current recommendation is that clinicians outline the particular child’s profile of strength and deficit, recognising that this profile may change over time.

    Phonology/speech sounds: Phonology is concerned with the rules that govern how sounds are combined together in words. Children with phonological deficits may fail to distinguish between certain speech sounds, such as ‘t’ and ‘k’, so that ‘cat’ is produced as ‘tat’. While these sorts of phonological errors are common in typically developing toddlers, some error patterns are atypical (e.g. replacing ‘t’ with ‘k’ so that ‘cat’ becomes ‘kak’), and most errors resolve by the time children are 4–5 years old (Bowen, 2015). Persistent phonological deficits may reduce intelligibility of speech and difficulties identifying and manipulating speech sounds within words (phonological awareness) is associated with difficulties learning to read.

    Grammar/syntax: Grammar refers to the rules that govern how to combine words into sentences (syntax) and how to combine parts of words together such as adding grammatical endings to verbs like –ing or –ed (morphology). Grammar is often a disproportionate area of deficit for children with DLD. For instance, a child with DLD may say ‘him walk to school’, instead of ‘he walked to school with his friends yesterday’. Comprehension of sentences can also be affected, especially when word order does not convey who did what to whom. For instance, there may be difficulty understanding sentences like ‘the boy was chased by the girl’ as children with DLD may interpret this as the boy doing the chasing.

    Semantics: Semantics refers to children’s ability to understand the meaning of words and how words are related to one another. Children with DLD often have difficulties learning new words. They may therefore have limited vocabularies and the words they do know may not have the same depth of understanding seen in children with typical language development (McGregor, Oleson, Bahnsen, & Duff, 2013).

    Discourse and Pragmatics: Discourse refers to longer stretches of connected language, like conversation and narrative. Children with DLD very often have deficits in narrative (i.e. telling a story in a logical, coherent sequence) (Gillam et al., 2018) and may find it difficult to maintain the thread of conversation. Pragmatics refers to the appropriate use of language in social contexts. Pragmatic deficits may manifest as poor at turn-taking in conversation, maintaining the topic of conversation, or being able to repair conversations that breakdown by asking for clarification. Pragmatics may also refer to the comprehension and use of linguistic forms that rely on context to disambiguate meaning, for example, non-literal language like metaphors and idioms, or making an inference (Adams, 2002).

    Prevalence

    Prevalence estimates of DLD may vary depending on the severity criteria for language, and whether or not non-verbal ability is used as an exclusion criterion. The most recent UK population study (Norbury et al., 2016) yielded a prevalence estimate at age 5-6 years of 7.58%, equivalent to two children in every Year 1 class. An additional 2.34% of children met criteria for language disorder, but also had intellectual disability and/or another known biomedical condition, such as autism or Down syndrome. The functional impact of DLD was evident in that only 12% of children identified as having DLD met early curriculum targets.

    While clinical reports suggest more boys are affected, epidemiological studies have not identified sex differences in prevalence (Norbury et al., 2016; Tomblin et al., 1997). This suggests that girls may be under-identified in community settings.

    DLD rarely occurs in isolation and children with DLD are at increased risk for a range of co-occurring conditions including:

    • Attention deficit hyperactivity disorder (ADHD)
    • Motor deficit (e.g. Developmental Co-ordination Disorder)
    • Reading disorders (including both dyslexia and reading comprehension deficits)
    • Speech sound disorders
    • Social, emotional, and behaviour problems

    In adolescence, children with a history of DLD are twice as likely as peers without language disorder to experience internalising, externalising, and ADHD-type psychopathologies (Yew & O’Kearney, 2013) and approximately 1/3 of adolescents referred to tertiary child and adolescent mental health services have previously unidentified language disorder (Cohen et al., 1998).

    From school entry DLD is persistent and characterised by parallel rates of language growth relative to peers (Law, Tomblin, & Zhang, 2008; Norbury et al., 2017). As a consequence, there is currently little evidence that children with DLD are able to narrow the language gap with typically developing peers. Young people with DLD are therefore more likely to leave school with fewer academic qualifications (Snowling, Adams, Bishop, & Stothard, 2001) , and may experience on-going problems with employment, intimate relationships, and mental health (Conti-Ramsden, Durkin, Toseeb, Botting, & Pickles, 2018; Johnson, Beitchman, & Brownlie, 2010).

  • What we already know

    Causes

    A common perception in the general public is that DLD results from poor parenting and a lack of appropriate language input during development. While there are social gradients in language, such that DLD is more common in areas of socio-economic disadvantage (Law, Charlton, Dockrell, Gascoigne, McKean, & Theakston, 2017), it is in fact a much more complicated picture.

    There is strong consensus that DLD is heavily influenced by genetic factors (D. V. M. Bishop, 2006). This evidence comes from twin studies, in which two twins are growing up together in the same household. These studies capitalise on the fact that there are two different kinds of twins; identical twins, who share the same genes, and non-identical (fraternal) twins who are genetically different. The question twin studies try to answer is ‘how similar are twins on measures of language?’ As all twins are exposed to the same home environment, differences in the strength of similarity between identical and fraternal twins is suggestive of genetic influence. Numerous studies have shown that while non-identical twins may differ radically in their language skills, identical twins tend to be much more similar in language ability. Of course, there can be some variation in the severity and persistence of DLD in identical twins, indicating that non-genetic factors (such as chance experiences, differences in school or peer experiences, illness, etc.) affect the course of disorder, but it is unusual to find a child with DLD who has an identical twin with typical language.

    The recognition that genetic factors play a role also informs us about environmental circumstances. Many children with DLD will grow up to be adults with DLD. They will likely have lower levels of literacy and educational attainment (Snowling et al. 2001) and this may result in fewer opportunities to obtain high paying jobs (Conti-Ramsden et al. 2018; Johnson et al. 2010). Reading books to children or verbal communication may not come naturally to some parents of children with DLD. Thus, although there is considerable evidence that DLD is more common in children from socio-economically disadvantaged backgrounds, but this likely reflects both genetic and environmental vulnerabilities (D. V. Bishop, 2014).

    Just because genetic factors are important does not mean that we are powerless to intervene. Parent language input and conversation, education, and specialist language interventions can all make meaningful improvements to children’s language and communication skills.

    Diagnosis and assessment

    Longitudinal studies consistently demonstrate stability in language status from school entry, with greater instability when children are identified in the pre-school years (Bornstein, Hahn, & Putnick, 2016; McKean et al., 2017). More specifically, about 40% of children identified with language delay by age 4 have spontaneously resolved by school entry (D. V. Bishop & Edmundson, 1987). Early language skills predict small amounts of variance in later language ability (Duff, Reen, Plunkett, & Nation, 2015) and therefore universal screening is not recommended as it is not reliable enough and identifies too many false positives (D. V. Bishop, Snowling, Thompson, Greenhalgh, & consortium, 2016).

    Consideration of multiple risk factors may improve identification (Christensen, Taylor, & Zubrick, 2017). Risk factors associated with persistent DLD include:

    • Family history of language or literacy deficits
    • Socio-economic disadvantage
    • Poor maternal education
    • Lower non-verbal cognitive abilities
    • Early developmental delays

    DLD in the classroom may be difficult to notice if the child is quiet and able to follow the actions of other children in the classroom, without truly understanding the language or instructions. Teachers are more likely to notice obvious speech problems and/or behaviour difficulties, difficulties learning core curriculum content, and problems with learning how to read. Children presenting with such difficulties in the classroom should be referred for a language assessment.

    Speech-language therapists are the primary professionals charged with assessment and diagnosis of DLD in the UK, though a multi-disciplinary team may be required for differential diagnosis of an associated biomedical condition. Associated conditions may include:

    • autism spectrum disorder (ASD)
    • sensori-neural hearing loss
    • neurodegenerative conditions
    • brain injury
    • acquired epileptic aphasia in childhood
    • genetic conditions such as Down syndrome
    • cerebral palsy
    • intellectual disability

    Diagnosis of DLD requires the following:

    • The child has significant language deficits relative to age expectations that create obstacles to communication or learning in everyday life,
    • The child’s language problems are persistent and unlikely to resolve by five years of age,
    • The problems are not associated with a known biomedical condition, as listed above

    Diagnosis will involve parent/carer interview of family history, observation of the child’s language and communication strategies in everyday contexts, and direct assessment of language skills using standardised assessment. Tomblin (Tomblin et al., 1997) proposed that assessment focus on the EpiSLI criterion: five composite scores representing performance in three domains of language (vocabulary, grammar, and narration) and two modalities (comprehension and production); clinicians may rely more heavily on omnibus tests of language, and measures of narrative ability have been shown to have good prognostic ability (D. V. Bishop & Edmundson, 1987). Cut-off scores on these measures are arbitrary, though typically children scoring in the lowest 7-10% on two or more composite scores are identified as having DLD. Test scores should always be considered in relation to functional impact (i.e. how language is impacting on school, social relationships, and self-esteem) in the diagnostic process.

    Treatment

    Currently, treatment for DLD is variable and many common approaches lack a sound evidence base. Service delivery may be focused on ‘tiers’ or ‘levels’ of intervention, including Universal approaches designed to benefit all children (e.g. specific training packages for education staff focused on enhancing language development), Targeted interventions that may be aimed at children with less severe deficits and carried out by non-specialist providers, and Specialist services in which SLTs provide direct and/or individualised treatments to children with the most-significant needs (Ebbels, McCartney, Slonims, Dockrell, & Norbury, 2018).

    Large scale, high-quality randomised controlled trials are still relatively uncommon in the field and this makes it difficult to assess clinical efficacy (see Law, Dennis, Charlton, 2017, Cochrane Review protocol for overview). Children’s language will improve over time, and without controlled studies, it can be hard to know how much of observed change is down to a specific treatment approach (cf. (Wake et al., 2011). In general, trials show significant, positive treatment effects for direct interventions with specific language targets including vocabulary, expressive grammar, and some elements of narrative and discourse (see Ebbels et al. 2018 for a summary). Receptive language skills appear much more resistant to treatment. Large scale studies of targeted language interventions show more variable outcomes (Bleses et al., 2017) and at best, modest treatment effects (Burgoyne, Gardner, Whiteley, Snowling, & Hulme, 2017; Fricke et al., 2017). Available evidence suggests that interventions in which education staff are asked to be the main delivery agents of SLT intervention, without on-going monitoring and support from specialist services (i.e. the “consultative” approach) are not effective (McCartney, Boyle, Ellis, Bannatyne, & Turnbull, 2011).

    The take home message seems to be that children with DLD can learn aspects of language that they are specifically taught, but this learning rarely generalises to other aspects of language or other academic/developmental skills. In addition, changing a language trajectory remains challenging and is likely to take considerable time and on-going effort.

  • Areas of uncertainty

    Despite recent advances in understanding the biological basis of DLD, we are still a long way from understanding how various genetic risk factors influence brain development, how differences in brain development affect learning, and why these differences would have disproportionate effects on language learning (Krishnan, Watkins, & Bishop, 2016). Nor do we fully understand how genetic and environmental influences interact to yield the heterogeneous profile of DLD that we see.

    We don’t know whether or how language disorders could be prevented, in part because early assessment of language is less reliable and therefore not strongly predictive of later language ability (Bornstein & Putnick, 2012).  Many practitioners and policy makers advocate for early intervention, but a large percentage of young children will make significant language improvement without intervention. Prioritising the under-5s could therefore result in treating large numbers of typically developing children and divert precious therapy resources from children with persistent language learning needs (Norbury, 2015). On the other hand, resolving language disorder after the age of 4 is challenging. We need to know if there is an optimal age to intervene, and whether there may be periods later in development when intensive intervention may be particularly beneficial.

    We know that children with DLD are at increased risk for poor social, emotional, and behavioural outcomes. We don’t understand the mechanisms that underpin this risk but school failure (Tomblin, Zhang, Buckwalter, & Catts, 2000), variable education provisions (Bao, Brownlie, & Beitchman, 2016), poor peer negotiating skills (Im-Bolter, Cohen, & Farnia, 2013) and poor emotion recognition/regulation (Salmon, O’Kearney, Reese, & Fortune, 2016) are all potential candidates. Given the large numbers of children with DLD presenting to CAMHS services, we urgently need to know how children with DLD access ‘talking therapies’ and what modifications to standard psychological treatments are required to ensure maximum benefit for children with DLD and their families.

    Our intervention evidence base is improving all the time, but we are still a long way from understanding what kinds of interventions work best, when, and for whom. In general, short periods of intervention may be sufficient to teach new vocabulary or grammatical forms (Ebbels, van der Lely, & Dockrell, 2007), but making significant improvements to a child’s overall language function is likely to take considerable time and sustained input (McCartney, 2017). We do not know the impact of common co-occurring conditions, such as general cognitive deficits, attention deficits, motor deficits, on response to treatment, or whether improvements in language functioning generalise to other aspects of development (e.g. improved social skills, behaviour, academic attainment).

    Providing the dosage necessary to make significant change in language proficiency remains an on-going challenge given limited therapeutic resources. Robust studies of on-line or computerised interventions for language are almost non-existent and urgently needed to evaluate whether such approaches could supplement face-to-face interventions.

  • What's in the pipeline?

    Previously, brain imaging studies of DLD have focused on the integrity of left hemisphere language regions in the developing brain. More recently, researchers have focused on neural circuits involved in learning and memory, particularly circuits involved in learning motor sequences and statistical regularities in language input (Krishnan, Watkins & Bishop, 2016). Such studies could elucidate how interventions might circumvent language learning obstacles, either by increasing input, or providing more explicit cues to learning.

    Many children with DLD are not referred to clinical services, or may wait a long time for speech-language therapy assessment. While speech-language therapists have traditionally been employed by the NHS, more and more education services are buying therapy time directly. Therapists working in collaboration with education staff may facilitate more direct links between the child’s language needs and how these impact social and academic demands of the classroom.

    There is increasing recognition that children with DLD grow up to be adults with considerable language needs. To date there has been little research on this population and few, if any, services to support them. Researchers and stakeholders are now exploring ways to identify these adults and what they require in terms of skills development, employment, and mental health.

  • Useful resources and websites

    Afasic: Parent-focused charity for families of children with DLD.

    The Communication Trust: The What Works database is a searchable database of commonly used intervention programmes and a rating of the quality of evidence available for that programme.

    ICAN: Communication charity providing information and support to the children’s workforce

    Royal College of Speech Language Therapists

    speechBITE: Australian database curating published trials of intervention and treatment efficacy searchable by language domain

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The Parent Blame Game

Seventy years ago Leo Kanner published his seminal paper describing autism In that paper he also coined the...

by Courtenay Norbury

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