Neurodevelopmental disorders: are our current diagnostic labels fit for purpose?


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Slides from a talk given at University of Western Australia on Tuesday 2nd October 2012, This lecture was co-hosted by the ARC Centre of Excellence in Cognition and
its Disorders and the Institute of Advanced Studies, University of Western Australia

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Neurodevelopmental disorders: are our current diagnostic labels fit for purpose?

  1. 1. Neurodevelopmental disorders: are ourcurrent diagnostic labels fit for purpose? Dorothy Bishop Wellcome Principal Research Fellow Department of Experimental Psychology University of Oxford
  2. 2. Meanings of ‘neurodevelopmental disorder’ Neurological disorders with known prenatal cause (genetic or acquired)  e.g. Williams syndrome, fetal alcohol syndrome Disorders where abnormal neurodevelopment is inferred: actual cause is complex or unknown  e.g.developmental dyslexia, autistic disorder, specific language impairment (SLI), developmental coordination disorder (DCD), developmental dyscalculia2
  3. 3. Common characteristics of neurodevelopmental disorders Defined in terms of behaviour Often use medical terminology, drawing parallel with acquired disorders Tend to be familial No single biological cause Male preponderance in most3
  4. 4. Do children fall neatly into these categories?4
  5. 5. Kaplan et al, 2001 • Sample of 179 children and families recruited from clinics, special schoolsDevelopmental co-ordination • All had dyslexia and/or disorder, 17% ADHD • Comprehensive assessment for ADHD, dyslexia, DCD, and psychiatric disorders ADHD, 65%Dyslexia, 70% “Comorbidity is the rule, not the exception” Gilger and Kaplan, 2001
  6. 6. Western Australian study 608 children aged 3 – 14 years  449 Typically-developing  30 Autism spectrum disorder (ASD)  24 Mental retardation (MR)  30 Receptive-expressive language disorder (SLI)  22 Developmental co-ordination disorder (DCD)  53 Attention deficit hyperactivity disorder (ADHD)  Assessments of IQ, language, motor, attention, social cognition, executive functionDyck, M. J., et al. (2011). The validity of psychiatric diagnoses: The case ofspecific developmental disorders. Research in Developmental Disabilities,32(6), 2704-2713.
  7. 7. Dyck et al: Discriminant function analysis Typical Autism MR SLI DCD ADHD
  8. 8. Same child, different diagnosis  Educational psychologist: Dyslexia  Speech-language pathologist: SLI  Psychiatrist: Autism spectrum disorder (ASD)  Neurologist: Developmental co-ordination disorder (DCD)  Paediatrician: ADHD
  9. 9. Questions Are these valid diagnostic categories? What is the impact of labels?
  10. 10. Public perception of diagnostic label  Explanatory force  Symptom complexx Qualitatively distinct from other disorders  Known cause
  11. 11. Which is true? He can’t read because he has dyslexia Dyslexia is a term applied to children who find it hard to read for no obvious reason cf. Erythema
  12. 12. Distinctive symptoms?Rutter and Yule (1975) No clustering of the developmental anomalies that are said to characterize dyslexia.• "In short, there has been a complete failure to show that the signs of dyslexia constitute any meaningful pattern." p 194• "If there is no recognisable pattern, then in the present state of knowledge there is no means of determining whether anyone has the hypothesized condition. Some kind of biological marker would be needed and so far none has been found."
  13. 13. Distinctive symptoms?Stanovich (1994) Poor readers very similar cognitive profiles, regardless of IQ Same phonological core deficit in both high and low IQ
  14. 14. Twin Study MethodTwins growing up together are expected to resemble each other MZ twins: genetically identical DZ twins: share 50% of polymorphic genes Question: Is concordance for disorder higher in MZ than in DZ twins? Most studies of dyslexia find YES Grigorenko, E. L. (2004). Genetic bases of developmental dyslexia: A capsule review of heritability estimates. Enfance, 56, 273-288.
  15. 15. A recent study shows that variations in a gene called DCDC2 may disruptthe normal formation of brain circuits that are necessary for fluentreading, leading to dyslexia. After further research, genetic screeningfor these variations could identify affected children early in theirlives and possibly prevent the misdiagnosis of other learning disabilitiesthat resemble dyslexia.“We have good statistical data that variations of the DCDC2 gene arestrongly associated with reading disability, also known as dyslexia. Theseresults reconfirm that dyslexia is strongly genetic and is not aconsequence of just environmental factors,” says lead investigatorJeffrey Gruen, M.D., Associate Professor of Pediatrics at Yale UniversitySchool of Medicine in New Haven, Connecticut. 15
  16. 16. So is it like this? Copyright:
  17. 17. High heritability ≠Single major gene 17
  18. 18. Genetics: Reality check DCDC2 is one gene that has been associated with dyslexia in several studies Scerri et al (2011) found a SNP on this gene where the association was significant at p = .005 The risk allele was found in: • 23% of controls • 31% of dyslexics
  19. 19. General population sample 100 children 10% dyslexic 90 OK 10 dyslexic 23% 31% Risk variant Risk variant * * 21 69 3 7 With risk variant • Most people with the ‘risk’ allele won’t have dyslexia • Most people with dyslexia won’t have the risk variant
  20. 20. Brain biomarkers 20
  21. 21. BBC website on Dyslexia
  22. 22. Brain regions found to differ structurally in dyslexics vs normal readers • Corpus callosum sizeinferior frontal precentral gyrus (motor control) • White matter gyralgyrus (speech depthproduction) • Right cerebellum grey matter • Auditory cortex size • Precentral gyrus grey matter • Pars triangularis, frontal lobe, size and shape • Asymmetry of planum auditory cortex temporale (> and <) (hearing) • Sylvian fissure length/position cerebellum (automatisation of skill) • Temporo-parietal white matter microstructure • Relative proportion of frontal and posterior N.B. Much within-group variation cortex
  23. 23. Functional brain imaging
  24. 24. Children withreading disabilitydisplay under-activation ofa network of left-lateralized areasduring reading,includingoccipito-temporal,temporo-parietal,and inferior frontalcortical regions Shaywitz, 2003
  25. 25. Cause or consequence of reading problems?
  26. 26. Experience affects the brain Dehaene et al, 2010: compared:  31 schooled/literate adults  22 unschooled ex-illiterate adults  10 unschooled illiterate adults All from Brazil or Portugal
  27. 27. Activation of visual word form area by written words literate ex-illiterate illiterate
  28. 28. Activation of language areas by spoken language Literate Ex-illiterate Illiterate
  29. 29. Implications for functional imaging studiesof dyslexia Dyslexic-non- dyslexic differences could be consequences of poor reading, rather than causes
  30. 30. Public perception of diagnostic labelx  Explanatory forcex  Symptom complexx  Qualitatively distinct from other disordersx  Known cause
  31. 31. General issues for neurodevelopmentaldisorders SLI ASD dyslexia ADHD Overlap at behavioural level Also overlapping causes and neurobiology
  32. 32. One alternative Broad category of ‘neurodevelopmental disability’ to establish need for services ‘Disability’ emphasises impact on individual ‘Neurodevelopmental’ emphasises biological basis: not just poor teaching Supplemented with assessment to establish profile of difficulties/strengths on different dimensions, and determine which services to prioritise
  33. 33. Advantages Avoids need for multiple diagnoses Encourages multidisciplinary assessment Avoids misleading notions of medical syndrome
  34. 34. Disadvantages Labels such as dyslexia, autism, ADHD now well-established; provide useful nexus for support groups, etc. Widespread tendency to assume that if there isn’t a medical label, there isn’t a serious problem • The problem is just a ‘social construct’ or worse still, an ‘excuse’
  35. 35. Sternberg & GrigorenkoOur Labeled Children (1999) Schools have financial interest in identifying specific learning disabilities Teachers “let off the hook”; "Often, the problem is not what is being taught but how it is being taught" “.. diagnosis as it now exists has provided some children who seem to be underachieving, based on their socioeconomic status, a way out"
  36. 36. Labels can be helpful: but how to choose them?
  37. 37. A tale of two disordersDEVELOPMENTAL DYSLEXIA SPECIFIC LANGUAGE IMPAIRMENT Unexpected difficulty in learning to read  Unexpected difficulty in learning to talk Not explained by lack of  Not explained by lack of opportunity to learn opportunity to learn Not explained by  Not explained by visual/hearing problems, low visual/hearing problems, low IQ IQ Not due to brain damage or  Not due to brain damage or known syndrome known syndrome (DEVELOPMENTAL DYSPHASIA)(SPECIFIC READING DISABILITY) Prevalence 3-7% Prevalence 5-10%
  38. 38. Dyslexia/SLI – good and poor memes“Why is it more desirable to have dyslexia than to have a reading disability?Why does no one other than speech-language pathologists and related professionals seem to know what a language disorder is?Why is Asperger’s syndrome, a relatively new disorder, already familiar to many people?” Kamhi, A. G. (2004). A memes eye view of speech-language pathology. Language Speech and Hearing Services in Schools, 35(2), 105-111.
  39. 39. Memes: What Are They?“Examples of memes are tunes, ideas, catch-phrases, clothes fashions, ways of making pots or of building arches. Just as genes propagate themselves in the gene pool by leaping from body to body via sperms or eggs, so memes propagate themselves in the meme pool by leaping from brain to brain via a process which, in the broad sense, can be called imitation.” R. Dawkins
  40. 40. Successful meme Easy to understand, remember, and communicate to others: May be influenced by whether confers advantage to the person communicating Survival does not depend on whether they are useful, true, or potentially harmful
  41. 41. Dyslexia has survived many attacks!Terminology in published papers Dyslexia Specific reading disability Specific reading retardation (Rutter & Yule) Developmental reading disorder (DSMIV)1985-1989 1990-1994 1995-1999 2000-2004 2005-2009
  42. 42. Amount of research (1985-2009) and prevalenceof neurodevelopmental disorders papers freq.Condition /year %Tourette syndrome 83 0.5Autistic spectrum disorder 643 0.7Developmental dyscalculia 9 3.0Attention deficit hyperactivity disorder 505 5.0Developmental dyslexia 152 6.0Developmental coordination disorder 16 6.5Specific language impairment 46 7.4 Bishop, D. V. M. (2010). Which neurodevelopmental disorders get researched and why? PLOS One, 5(11), e15112. doi: 10.1371/journal.pone.0015112
  43. 43. Research funding and frequency of neurodevelopmental disorders NIH spend $Condition 2000-2009 freq. %Tourette syndrome 252,709,203 0.5Autistic spectrum disorder 2,613,298,181 0.7Developmental dyscalculia 4,355,095 3.0Attention deficit hyperactivity disorder 2,205,461,058 5.0Developmental dyslexia 136,012,937 6.0Developmental coordination disorder 4,093,060 6.5Specific language impairment 125,035,522 7.4 44
  44. 44. Labels have consequences Medical-sounding labels get taken seriously Conditions with medical-sounding labels attract more research funds • But not always successful: dyscalculia and dyspraxia have not been successful memes • May also depend on the professional group with principal responsibility (power, gender) And a good meme may include or even induce positive features of disorder
  45. 45. Positive connotations of labels So as I’m reading the narration into a tape recorder, it started to dawn on me. I’m not lazy. I’m not stupid. I’m dyslexic!” Henry Winkler Autism in Positive Light
  46. 46. In conclusion Naïve to imagine we could abandon terms such as ‘dyslexia’ Adverse consequences would include:  Fewer children having problems recognised  Increase in tendency to blame all problems on poor parenting/schooling  Less research into biological bases But need to be aware this (and other neurodevelopmental disorders!) is a fuzzy category, and does not explain anything Children need multidisciplinary assessment Question of what to do about ‘cinderella’ conditions: SLI, dyscalculia, dyspraxia
  47. 47. Raising Awareness of Language Learning Impairments
  48. 48. Dorothy Bishop Oxford Study of Children’sCommunication Impairments,Department of Experimental Psychology, South Parks Road, Oxford, OX1 3UD,