The prevalence of ASD and ADHD

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The prevalence of ASD and ADHD

• Christopher Gillberg, MD, PhD
• Glasgow March 2006

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Christopher Gillberg

• Professor of Child and Adolescent Psychiatry
• University of Göteborg (Queen Silvias Hospital)
• NCYPE
• Strathclyde University (Yorkhill Hospital)
• University of Bergen (Haukeland sygehus)

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Autism and ADHD prevalence

• How common is autism?
• How common are autism spectrum conditions (ASC)?
• How common is ADHD?
• Whats the degree of overlap?

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How common is autism?

• Up until about 1990 everybody seemed to agree
  that autism was very rare, occurring in mo more
  than 5 in 10,000 children
• However, long before that, Wing Gould (1979),
  and Gillberg (1983) had suggested that autistic
  features and autism spectrum conditions were very
  much more common
• In fact, the Gillberg study (1983) suggested that
  69 in 10,000 Swedish 7-year-olds born in 1971 had
  marked autistic features (triad symptoms)

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How common is autism?

• In 1991, Gillberg published a paper in the
  British Journal of Psychiatry, entitled Is
  autism more common now than ten years ago?,
  suggesting that it was more common than
  previously believed, but that it probably wasnt
  really more common than in the past
• That same year, he suggested, in his Emanuel
  Miller memorial lecture, that autism and
  autistic-like conditions might best be
  conceptualized as a spectrum of disorders in the
  lower portion of normally distributed empathy
  skills
• Some authorities, particularly Michael Rutter and
  his group, were outraged, and insisted that
  autism and Asperger syndrome were extremely rare
  disorders, and that autism was the best
  validated, easiest to delineate, and most
  reliably diagnosable child psychiatric disorder

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How common is autism?

• In 1999, Gillberg Wing did a comprehensive
  review of all English-language papers ever
  published on autism in the general population,
  concluding that autism (1) was indeed much more
  common than previously believed, (2) had
  undergone change as regards basic concepts and
  diagnostic criteria, (3) was now better
  acknowledged among the public, and that (4)
  better awareness and services all contributed
  towards a steady 3-4 increase every year from
  the 1960s through the 1990s
• Wing Potter (2002) suggested that about 1 of
  the general population of school age children
  might be suffering from autism spectrum
  disorders (including autism, atypical autism,
  and Asperger syndrome)

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Agreement on the prevalence of autism spectrum
conditions?

• In the past decade, other authors, including Eric
  Fombonne (2005), and several US groups have
  reported similarly high rates of autism as were
  reported many years ago by Wing and Gillberg
• Virtually all studies published since 1999 have
  come up with general population school age
  prevalence rates for autistic disorder of 11-30
  in 10,000 children and for Asperger
  syndrome/atypical autism (sometimes referred to
  as PDDNOS) of another 40-50 in 10,000 children,
  i.e. a total of well above half a per cent of the
  general population, with the majority of studies
  reporting figures in the range of 0.6-1.1 for
  autism spectrum disorder (or ASC) total
• This is in exactly the same range as the 0.69
  reported by Gillberg in 1983 in children born in
  1971

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Agreement on the prevalence of autism spectrum
conditions?

• Thus, there is emerging agreement on the
  prevalence of ASC based on the diagnostic
  criteria systems currently in use
• However, there is no agreement as to whether or
  not prevalence rates have actually gone up
• Nevertheless, most authors favour the view that
  the true rate has not gone up
• Autistic disorder is probably c. 0.2 of the
  general population
• There is some agreement regarding the rate of
  Asperger syndrome as diagnosed on the basis of
  Gillberg Gillberg (1989) criteria (c. 0.4),
  but no agreement on the rate of this disorder on
  the basis of ICD-10/DSM-IV criteria for
  Aspergers disorder

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Associated fetaures in ASC

• Malefemale ratio 2-71
• Medical disorders 12-37
• Epilepsy 20-38
• Motor problems majority
• Visual and eye-tracking problems about half?
• Hearing impairments deafness 2, severe hearing
  loss 10?
• Psychiatric and behavioural disorders majority
• Gastrointestinal problems half??
• Sleep problems half??

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How common is ADHD?

• Widespread agreement that ADHD is a common
  condition, but reported prevalence figures range
  from about 2 to about 12 per cent (DSM-IV)
• Most studies are in the range of 4-7 per cent for
  school age children
• About half of these still meet full criteria by
  early adult age (and majority of the other half
  have remaining symptoms)
• 45 AD, 45 AD/HD, and 10 HD?
• No indication that prevalence is increasing

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Associated features

• Malefemale 31 (lower among adults)
• Epilepsy ? (ADHD common in epilepsy)
• Medical disorders (e.g. FAS, Fragile X, 22q11)
  5?
• Visual (including eye-tracking) problems ?
• Hearing impairment ?
• Motor problems (DCD) 50
• Academic problems 40-90
• Psychiatric and behavioural problems 85
• ODD/CD/APD
• Depression and anxiety
• Tic disorders
• Autistic features (particularly in those who also
  have DCD)

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ASC-ADHD overlap

• About half of all young people with ASC are
  hyperactive and most of these would meet
  diagnostic criteria for ADHD
• Many of the others are very hypoactive
• Children with severe ADHD have autistic features
  in about half of all cases when there is
  concomitant DCD, but very rarely if there are no
  motor incoordination problems

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Clinical implications

• ASC exist in 0-5-1.1 of the population and is
  suspected in many more (life-long) services need
  to be aware of this proportion (most will need
  extensive services)
• ADHD exists in 5 of the population of school age
  children and at least half of these will need
  rather extensive services for many years
• Clinicians working with one type of problem will
  always come across many cases of the other type
• Thus, there is a need for neuropsychiatric and
  neurodevelopmental teams rather than teams
  specifically for ASC or ADHD