**1. Introduction**

Children with autism spectrum disorders (ASD) have a higher risk of suffering from several other conditions. In this chapter I review the extent to which autistic individuals can also expe‐ rience a range of other difficulties, but my focus will be on the common neurodevelopmental disorders. The most common of these include dyslexia, attention deficit hyperactivity disorder (ADHD), dyspraxia, specific language impairment, and dyscalculia. There is considerable symptom overlap in particular between ADHD and dyslexia, and like autism both are descri‐ bed as developmental disorders by psychiatric classification systems (American Psychiatric Association, 2000; World Health Organization., 1992). Overlapping conditions are termed 'comorbidity' by medical practitioners. Co-morbidity may reflect the greater difficulties experi‐ enced by children with a combination of deficits. Sometimes it is apparent that many children with a developmental disorder could be classified in several ways. Here I will firstly examine the research evidence that examines how often symptoms of dyslexia and ADHD occur in the population of autistic children, and second, review the various theories that have tried to ex‐ plain why such co-occurring difficulties are so common.

'Comorbidity', a term used in medical literature to mean a dual diagnosis, or multiple diag‐ noses, can reflect an inability to supply a single diagnosis that accounts for all symptoms. Children with ASD have been shown to have higher rates of epilepsy, with 30% of cases having epilepsy comorbid (Danielsson, Gillberg, Billstedt, Gillberg, & Olsson, 2005). Other conditions that are commonly co-morbid with ASD include hearing impairment (Kielinen, Rantala, Timonen, Linna, & Moilanen, 2004) mental health and behavioural problems (Brad‐ ley, Summers, Wood, & Bryson, 2004), including anxiety, and depression (Evans, Canavera,

© 2013 Russell and Pavelka; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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

dren who have difficulties with reading and spelling as well as other generalized intellectual disabilities. The implications of including this group as dyslexic mean that more children with an intellectual disability would also be classified as 'dyslexic'. As ASD includes a large group with intellectual disability the extension is likely to increase the number of children who may be classified as having both conditions. This is important as the clinical and educa‐

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

Hyperactivity Disorder

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In addition to these characteristics, dyslexic children may experience visual and auditory processing difficulties, similar to hyper or hypo sensitivity often associated with ASD. Like the 'islets of ability' seen in many children with ASD, some dyslexic children may also have

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

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

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

tion label may determine the interventions a particular child receives.

strengths in particular areas, such as design, logic, and creative skills.

infrequently alone and symptoms starting before seven years of age.

that extends into the population at large.

**3. ADHD**

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 ADHD and dyslexia.

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 and ADHD manifest themselves.
