**3. ADHD**

Kleinpeter, Maccubbin, & Taga, 2005). It has also been shown that parents of autistic chil‐ dren are twice as likely themselves to have suffered from psychiatric illness than parents of

Most of these problems are distinct from those examined in this chapter: the common devel‐ opmental disorders of childhood which are also found to co-occur with autism, particularly

Before reviewing the evidence that suggests many children share difficulties symptomatic of these conditions, and the theories of why this may be, I will briefly describe how dyslexia

Dyslexia is conceptualized by both educational bodies and the psychiatric classification sys‐ tems as a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling. Characteristic features of dyslexia are difficulties in phonological awareness, verbal memory and verbal processing speed. Dyslexia is developmental delay in literacy and generally slow and inaccurate reading and spelling. The definition of dyslexia has changed over time, and such changes have often been based on the research identifying a range of associated difficulties that occur with dyslexia. Estimates of the prevalence of dyslexia have been complicated because dyslexia cut-offs are contested (Coltheart & Jackson, 1998) and dys‐ lexia manifests itself differently in various languages according to levels of phonic regularity (Miles, 2004). Research over the last 40 years has focused on phonological skills. These are the reading and de-coding skills used when breaking down language into its component sounds

Like autism, dyslexic difficulties are considered to exist in a continuum throughout the general population (Fawcett, 2012). There is much interest in the association of cognitive ability with changing symptom profiles and diagnosis. The definition of dyslexia is in flux, and has been re‐ cently redefined by many national bodies, for example in the UK, the British Psychological So‐

Dyslexia is evident when accurate and fluent word reading and/or spelling develops very incompletely or with great

This definition implies that the problem is severe and persistent despite appropriate learn‐ ing opportunities. This UK definition differs from the ICD-10 diagnosis of developmental dyslexia or 'Specific Reading Disorder', which requires a discrepancy between actual read‐ ing ability and the reading ability predicted by a child's IQ. So an intellectual disability, (generally considered IQ below 70) can co-occur with the British Psychological Society defi‐ nition of dyslexia. This new definition includes the so called 'garden variety' dyslexic chil‐

ciety, focusing on literacy learning at the 'word level' without attainment discrepancy:

non-autistic children (Daniels et al., 2008).

362 Recent Advances in Autism Spectrum Disorders - Volume I

and reassembling the parts in order to read or to spell a word.

ADHD and dyslexia.

**2. Dyslexia**

and ADHD manifest themselves.

difficulty (British Psychological Society, 1999)

ADHD is known as 'Hyperkinetic Disorder' in ICD-10; there are three subtypes of ADHD according the DSM. In the first, a child will primarily have problems with attention which may manifest as an inability to remain 'on task' for long periods, lack of response to instruc‐ tion or distractibility. In the second sub-type, symptoms of hyperactivity and impulsivity dominate, which is characterized by wriggling, squirming, being unable to sit still, inter‐ rupting and finding it difficult to wait. Children may also be climbing in inappropriate sit‐ uations and always on the move when free to do so. The third sub-type is simply the coexistence of both attention problems and hyperactivity, with each behavior occurring infrequently alone and symptoms starting before seven years of age.

According to ICD-10, eventually, assessment instruments should develop to the point where it is possible to take a quantitative cut-off score to assess ADHD. Like dyslexia and autism, the symptoms are behavioural in nature, and are part of a continuously distributed pattern that extends into the population at large.

The persistence of ADHD symptoms is not so marked as for autism. Around 70 to 50 per‐ cent of those individuals diagnosed in childhood do not continue to have symptoms into adulthood (Elia, Ambrosini, & Rapoport, 1999). There is evidence suggesting to some extent symptoms of ADHD are expressed in reaction to home (Mulligan et al. 2011) and other envi‐ ronmental contexts. Individuals with ADHD also tend to develop coping mechanisms to compensate for some or all of their impairments. ADHD is diagnosed more often in boys with the reported ratio varying from 2:1 to 4:1 (Dulcan, 1997; Kessler et al., 2005) though some studies suggest this may be partially due to referral bias where teachers are more like‐ ly to refer boys than girls (Sciutto, Nolfi, & Bluhm, 2004). Treatments for ADHD involve a combination of medication, usually methyphenidates which are well established in improv‐ ing symptoms of inattention, and behavioral intervention in education and at home. The is‐ sue of girls being overlooked on identification is a common thread for research in dyslexia, ADHD and autism. Our own results suggest there is some evidence to back up the claim that boys with ASD symptoms are given the diagnosis more frequently than girls with equivalent ASD symptoms (Russell, Steer, & Golding, 2011). This may be because the disor‐ ders tend to be conceptualized as 'male' leading to referral bias.

The imposition of a cut off between normality and abnormality is therefore 'an arbitrary but convenient way of converting a dimension into a category' as Goodman and Scott (1997, p.

Co-Occurrence of Developmental Disorders: Children Who Share Symptoms of Autism, Dyslexia and Attention Deficit

Hyperactivity Disorder

365

http://dx.doi.org/10.5772/54159

Various studies have looked for ADHD or ADHD symptoms in samples of children with autism or ASD. Rates of ADHD have ranged from 28% to 78% of these samples (Ronald, Edelson, Asherson, & Saudino, 2010). Studies that look at ADHD symptoms have reported even higher numbers: for example, Sturm, Fernell, & Gillberg, (2004) looked at a sample of around 100 high functioning children with ASD and found 95% had attention problems, 75% had motor difficulties, 86% had problems with regulation of activity level, and 50% had impulsiveness. About three-quarters had symptoms compatible with mild or severe ADHD, or had deficits in attention, motor control, and perception, indicating a considerable overlap

In an large analysis of nine hundred forty-six twins, Reierson and colleagues (2008) assigned DSM-IV ADHD diagnoses, and measured autistic traits using the Social Responsiveness Scale. The study showed that there are clinically significant elevations of autistic traits in children meeting diagnostic criteria for ADHD. These findings confirm results in earlier studies (Clark, Feehan, Tinline, & Vostanis, 1999). Santosh and Mijoovic (2004) which found children with ADHD had elevated levels of impairment in all three autistic symptom do‐ mains, namely social deficits, communication and stereotyped behaviors. Clark *et al* found 65-80% of parents of children with ADHD reported difficulties in social interaction (particu‐ larly in empathy and peer relationships) and in communication (particularly in imagination, and maintaining conversation). So the presence of autistic traits in children with ADHD ap‐

In an analysis conducted with Lauren Rodgers at the Peninsula Medical School in the UK using data from the Millennium Cohort Study, a cohort of around 19,000 children who were all born between 2000 and 2002, we noted 44 children had a dual diagnosis of both ASD and ADHD (proportion of total population 0.3%) by age seven. The prevalence of children with identified ADHD in the ASD sample was 17%. Conversely, the prevalence of children with ASD in the ADHD sample was higher at 27%. Both figures indicate substantial overlap be‐

Various European research groups have examined co-morbid disorders in adults with diag‐ nosed ASD. An international team lead by Hofvander studied a group of 122 adults with normal IQ from specialist clinics in three European cities: Gothenburg, Paris and Malmö (Hofvander et al., 2009). Here the overwhelming majority had symptoms of ASD. Nonverbal communication problems were also very common, described in 89% of all their subjects. In this study over half the participants, (52%) were diagnosed with co-morbid ADHD. Interest‐ ingly, participants diagnosed with pervasive developmental disorder. 'Not Otherwise Speci‐ fied' (PDD-NOS) diagnosis had significantly more symptoms of inattention and

**4. Evidence of symptom overlap – ASD and ADHD**

between these disorders and high-functioning ASD in children.

pears common (Ronald et al., 2010).

tween these conditions.

23) point out.

Because ASD, Dyslexia and ADHD are all behaviorally defined, so 'symptoms' are behaviours. All three conditions are conceived as particular behaviours along a spectrum, where traits have a continuous distribution and extend into the general (non-disordered) population. An arbitra‐ ry cut off point determines who is considered to be within the various categories and who is not. The clinician giving a diagnosis will be responsible for judging where this cut off may come, guided by diagnostic criteria and standards within disciplines as well as perceived im‐ plications: the benfits versus any possible risks of assigning a diagnosis. This is perhaps best es‐ tablished for autism: Constantino and Todd (2003) measured autistic traits in a large community sample, and found no jump in the threshold of autistic behaviours between 'nor‐ mal' individuals and those with an autism spectrum diagnosis, rather they found a continuous distribution. These findings concurred with those in a Scandinavian study (Posserud, Lunder‐ vold, & Gillberg, 2006). One of our own studies has likewise shown that autistic traits do ex‐ tend into the 'subclinical' population (Figure 1). As with dyslexia and ADHD, there is not a sharp line separating severity in those with a diagnosis from less severe traits in those without (London, 2007). In both dyslexia, ADHD and the autism spectrum, some children have more severe difficulties than others, and the symptoms extend into the population of children (and adults) as a whole. For dyslexia, there are many people who may have mild dyslexic difficul‐ ties but perhaps might not qualify as 'dyslexic'. For autism spectrum disorders, many people without an autism diagnosis do have autistic-type behaviours but the severity and frequency of those behavioural symptoms is less severe than in those deemed to qualify for a diagnosis.

**Figure 1.** The distribution of an ASD composite trait in the general population from Russell et al.(2012)

The imposition of a cut off between normality and abnormality is therefore 'an arbitrary but convenient way of converting a dimension into a category' as Goodman and Scott (1997, p. 23) point out.
