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

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

difficulty (British Psychological Society, 1999)

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‐

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

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‐ tion label may determine the interventions a particular child receives.

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