Dyslexia and Autism: Is there a Connection? (2023)

Autism spectrum disorders are often characterized by language impairments. Dyslexia also manifests in language deficits…which begs the question of a possible connection between the two.

An autism diagnosis may explain some of your child’s challenging behavior, but parents are often left wondering whether every symptom is autism related. To add to the confusion, autism is often found alongside other conditions like attention deficit hyperactivity disorder (ADHD), dyspraxia, anxiety, and sometimes dyslexia.

Language difficulties form part of communication deficits which is considered a core autism feature. This may be the reason parents feel confused: the source of your child’s difficulties may be autism related or he/she could have a comorbidity or co-existing condition in addition to his/her autism spectrum disorder which could account for language challenges.

In an attempt to clarify some of the confusion, autism and dyslexia will be defined separately in this article. Then the common symptoms and challenges will be examined to see where the two conditions overlap. Research will be consulted to determine whether a child can be diagnosed with dyslexia and autism, or whether the two are mutually exclusive.

In this regard, studies and scientific literature often speak about co-existing conditions and comorbidities. To start off, it may be helpful to define and clarify some of these terms—and the relation they bear to both autism and dyslexia.

Autism spectrum disorder (ASD) and comorbidities

A study reviewing the concept of comorbidities (Valderas et al., 2009) defined the term as the presence of more than a single distinct condition in an individual. The authors mentioned there is often disagreement when it comes to the meaning of the term and its application. The importance of mechanisms which underlie two existing conditions, and the implications of such mechanisms for clinical care is also considered in the study (Valderas et al., 2009).

When comorbidities and autism spectrum disorder were reviewed in an editorial (Casanova et al., 2020) the authors advocated for medical professionals to reorient services in a manner that better recognizes ASD comorbidities for improved outcomes. In this study a comorbidity was defined as the presence of a chronic disorder that co-occurs in tandem with the primary disease (Casanova, 2020).

While the term comorbidities may cause disagreement when it comes to a precise definition and implications, researchers are in agreement that comorbidities and coexisting conditions are highly prevalent in children and adolescents with autism spectrum conditions.

Researching the mechanisms and implications of underlying conditions in ASD become vital when one considers quotes like: “Treatment of comorbid medical conditions may result in a substantial improvement of quality of life both of the child and their parents. What investigations should be implemented can vary both within the autism spectrum and individually.” (Isaksen et al., 2012).

This may add to the worries of parents with a child on the spectrum. What if a symptom or behavior written off as just being part of autism, is actually the manifestation of a comorbidity or separate condition that requires a separate diagnosis and treatment plan?

Because even if research about the connection between autism and dyslexia is scant, parents with children on the spectrum do speak about autism occuring along with learning disorders like dyslexia. The question (which is complicated and requires more clinical testing) is whether a child’s learning and language difficulties arise because of autism symptoms or because the child is dyslexic.

Autistic children do unfortunately sometimes miss out on educational opportunities due to behavioral symptoms and challenges brought on by their condition—for example sensory difficulties could make classroom learning unbearable. Whether a child’s language lag is due to such factors, or a coexisting condition like dyslexia, may have to be deciphered by a developmental-behavioral pediatrician.

Could dyslexia be a comorbidity of an autism spectrum disorder?

Both autism spectrum disorders and dyslexia can be classified as neurodevelopmental conditions with rising prevalence amongst children. Officially an autism spectrum disorder is an exclusionary criterion for a diagnosis of dyslexia and vice versa (Russell & Pavelk, 2013).

There are, however, significant symptoms that are shared by these two conditions and which inform the opinion that, although autism and dyslexia are distinct conditions, they can occur in the same individual. Research concerning the connection between ASD and dyslexia is scant, but studies (Huang et al., 2020) have explored a gene (DOCK4) shared between the two neurodevelopmental conditions.

By exploring some background information about the two conditions, the symptoms that overlap can be identified. The most significant point of overlap lies in communication (or more precisely, language) deficits, which are a core symptom of both autism and dyslexia.

Autism

To get a better idea of how communication impairments in autism may overlap or present similarly to those found in dyslexia, the core criteria and symptoms of autism should be examined.

According to the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM–5; American Psychiatric Association, 2013) an autism diagnosis requires persistent impairments in social communication and social interaction in various contexts. Examples of how such deficits may manifest are provided—such as difficulties with social-emotional reciprocity and nonverbal communication. The communication deficits comprise the first core criteria, with restricted, repetitive behaviors and interest making up the second.

The DSM-5 diagnostic criteria for autism spectrum disorders also contains a note which specifies that if a child has definite social communication deficits, but he or she does not meet the other requirements for an autism diagnosis, an evaluation for the separate diagnosis of social (pragmatic) communication disorder should be considered.

The DSM-5 criteria for autism spectrum disorders also contains a directive that an autism diagnosis should specify if there is an accompanying language impairment. This is clearly significant as far as the overlap between symptoms of autism and dyslexia are concerned.

It is important to keep in mind that autism goes beyond difficulties in communicating effectively; autistic individuals also have restricted and repetitive behaviors and interests and they mostly have sensory processing difficulties, too. Dyslexia is a developmental language disorder, where most symptoms are language related.

Dyslexia

Most of us feel we have a pretty good idea of what dyslexia is, but when it comes down to defining the condition we often fumble and perpetuate the myth that it has something to do with letter (or symbol) reversal and reading words backwards. While this may be one of the symptoms of dyslexia, not everyone with dyslexia will exhibit reversals and it is far from the defining characteristic of this neurodevelopmental condition.

Some advocate for the definition of dyslexia to remain uncomplicated, they feel it should simply be stated as a difficulty with words. The word dyslexia can be broken down into the latin word dys (meaning difficult or poor) and the Greek word lexia (which translates to words).

In the DSM-5, dyslexia is categorized as a “specific learning disorder” (American Psychiatric Association, 2013). The formal definition of dyslexia, adopted by the International Dyslexia Association (IDA) in 2002 reads as follows: Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.” (https://dyslexiaida.org/definition-of-dyslexia/)

Language practitioners and speech pathologists caution against seeing the disorder in a singular light—such as a difficulty with reading. Rather the condition may encompass many comorbid deficits like auditory, memory and language-based difficulties, and it may cause learning challenges not only in reading but also spelling, handwriting, and working memory. It is important to note that dyslexia is not related to low intelligence, many dyslexic children have a normal or above average IQ.

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Much deeper than mirror writing…

The idea or myth mentioned above—that dyslexia is simply a learning disability where children reverse letters and numbers and see words backwards—made dyslexia seem like a visual disturbance or challenge. This was proven in a study (Gonzalez & Brown, 2019) where findings indicated that even teachers upheld the prevailing myth that dyslexia is a visual processing disorder encompassing mirror writing and word reversal rather than a phonological processing disorder.

In contrast, a study (Shaywitz et al., 2006) mentions the cognitive basis of dyslexia. The authors refer to dyslexia as a language disorder with specific deficits in phonological processing.

The same study by Shaywitz et al. (2006) feels evidence of disruptions in the neural systems serving reading (such disruptions were proven by functional brain imaging) has far reaching implications for the acceptance of dyslexia as a valid disorder.

The difficulties caused by dyslexia can’t be denied, but diagnosing the condition has always been difficult. Some studies feel the existing definitions of dyslexia are to blame for unreliable diagnosis, possibly due to the fact that definitions of the disorder rely on a single indicator—for example deficits in decoding.

In his article titled Why is it so difficult to diagnose dyslexia, and how can we do it better?, Richard K.Wagener suggests diagnosis could be improved if rather than using a single factor model, a hybrid model for testing of dyslexia was employed. Such an evaluation system would account for many facets of reading and spelling development, and provide evaluators with a more complete picture of the individual being tested.

A holistic way of evaluating dyslexia may also be of importance when diagnosing a child with autism who shows such symptoms. Rather than focusing on a single indicator, like the above mentioned letter reversal, it is important to look at the child’s symptoms, medical history, comorbidities and any other relevant factors to obtain an accurate diagnosis.

Early signs of dyslexia, compared to signs and symptoms of autism spectrum disorders (ASD)

Parents sometimes voice concerns about language challenges experienced by their autistic child which they feel may be related to a lack of social motivation; these parents fear that inadequate social interaction opportunities may interfere with their child developing age appropriate language skills and abilities.

This may be one of the (debatable) contributing factors in language impairment in children with autism. In contrast the language difficulties in dyslexia cannot be attributed to factors like social motivation. Rather those with dyslexia have difficulty connecting spoken language and its printed equivalent because they have impairments in the phonological part of language (Roitsch & Watson, 2019).

How do such impairments manifest? The following are common signs of dyslexia:

Late-talking or delayed language acquisition

Difficulty in learning to speak, or a delay in language acquisition may be one of the earliest manifestations of both dyslexia and autism. Dyslexia is usually diagnosed later (when a child is around five or six years old and learning to read)t) while autism can be diagnosed from around two years of age. Studies advocate for early identification and early intervention when it comes to diagnosing children with autism spectrum disorders (Parmeggiani et al., 2019).

The authors of this same study discussed how a delay in spoken language is often the most common symptom leading to an initial medical consultation, or seeking of an autism diagnosis. This delay in spoken language includes both verbal production and understanding (Parmeggiani et al., 2019).

The positive impact of an early diagnosis (and intervention) apply equally to dyslexia. According to Dr. Sally Shaywitz: “The human brain is resilient, but there is no question that early intervention and treatment bring about more positive change at a faster pace than an intervention provided to an older child. The sooner a diagnosis is made, the quicker your child can get help, and the more likely you are to prevent secondary blows to her self-esteem.” (Shaywitz, 2004)

If there is a family history of dyslexia parents, need to be vigilant for signs such as late-talking or delayed language acquisition. A study by Snowling and Melby-Lervåg (2016) revealed that children with a family history of dyslexia showed early deficits in phonology when compared to their peers (without a family history of dyslexia). Importantly this study also showed that not all these children developed dyslexia.

Developmental milestones may be reached later in both autism and dyslexia. This includes more than just late-talking, milestones like learning to crawl, walk, and ride a bike may also be delayed. In autism spectrum conditions missed milestones may be masked as the child behaves very differently to typically developing peers.

Challenges and difficulties in learning sounds, letters, and sight words

If a child has a family history of dyslexia and he/she is also a late talker (no first words by 15 months) the child may have an elevated risk of developing dyslexia and the child should be monitored. Further signs to look out for include:

• Challenges in remembering easy nursery rhymes and/or difficulty recognizing rhyme
• Continued use of baby talk and constant mispronunciation of common words
• Difficulty with sequence, logic order, and following directions
• When the child starts learning to read, deficits become more apparent. He/she may struggle with the learning of letter names and continuously muddle up similar looking letters. Later spelling difficulties may lead to great frustration
• Word recognition will be challenging for a child with dyslexia. He/she may guess at certain words, omit others and stumble over words in addition to showing deficits in decoding words
• Decoding difficulties will lead to a struggle in identifying unknown words and fluency in reading will be affected
• It’s important to note that while letter reversal and reading backwards may occasionally be a sign of dyslexia, it’s actually pretty common for children to reverse letters as they learn to read and write

A struggle with acquiring language is a symptom of autism and dyslexia, but unlike dyslexia autism’s non-social cognitive processes could be to blame for notable constraints on language development (Eigsti & Schuh, 2016). Language impairment is considered a core characteristic of ASD, some autistic children never acquire functional language and remain nonverbal or nonvocal.

Language deficits in autism present differently than impairments in dyslexia. Children with autism often acquire language unevenly. In some autistic children regression may occur, which results in a loss of language comprehension and verbal expression.

Due to the spectrum nature of autism there is a great variation of language deficits among autistic individuals. Some autistic individuals possess savant skills in acquiring foreign languages while others describe their difficulties with functional language as a daily struggle.

Reading, spelling and handwriting difficulties

As mentioned before, the challenges of dyslexia become more apparent as children learn to read and write. As reading and writing depend on similar underlying processes, children with dyslexia often have writing difficulties (Graham & Herbert, 2010).

Handwriting challenges may apply to autistic children too. According to Fuentes et al. (2009) children with ASD showed a worse performance on handwriting tasks in comparison to age and intelligence matched children in the control group.

As far as reading deficits are concerned, an overview of neuroimaging studies titled Reading, dyslexia and the brain (Goswami, 2008) reveal that a convergence of studies show the dyslexic brain is characterized by under-activation of the vital neural networks for reading.

This biological basis of dyslexia disproves the hurtful sentiment that dyslexic children should just “try harder”. Once teachers and peers realize that, for dyslexic children, learning and reading difficulties may stem from deficits in processing the sound system of language, such myths will hopefully be dispelled.

With regards to reading in children with autism, the spectrum nature of the condition once again means some autistic individuals excel at reading while others face severe reading impairments. Reading impairments in autistic children are especially prevalent when it comes to comprehension. Autistic children may figure out how to decode words and appear to read well but comprehension of what they are reading may be negativelyaffected.

Children teaching themselves to read at an early age may have hyperlexia, a syndrome linked to advanced reading skills and an intense fascination with words. Advanced decoding skill with a lack of comprehension is a characteristic of hyperlexia. Hyperlexia is strongly associated with children on the spectrum (Ostrolenk et al., 2017).

Similarities and differences

As one peruses various studies, similarities and differences in dyslexia and ASD become apparent. Both conditions are life-long disorders even though they are often treated as childhood conditions. Both are neurodevelopmental in nature and the two conditions possibly have a shared candidate gene.

Although the two disorders share many overlaps it is also clear that the core symptoms of autism go beyond language impairments and deficits. An autism diagnosis relies on difficulties in two areas—social communication and restricted, repetitive behaviors or interests.

Reading through literature about dyslexia makes it clear that the definition causes a lot of difficulties. While most agree that dyslexia is a learning disability (or learning disorder) with neurological origins, the manifestation, symptoms and other factors are often disagreed upon. Perhaps a more fluent, multifaceted definition is needed in addition to more research about effectively and easily diagnosing dyslexia.

For children who struggle at school despite possessing average or high intelligence, the challenges with word recognition, poor spelling and decoding difficulties should be addressed with immediacy—problems associated with dyslexia may lead to anxiety and poor self-esteem.

Good news

Most experts agree that fluent reading can be taught to children with dyslexia, provided they attain the necessary support from teachers or professionals in a clinical setting and from parents (or caregivers) in the home environment. Impaired speech and language skills in autism can also be addressed through treatment options like Functional Communication Training, an evidence-based practice for individuals with ASD.

Parents who are worried about symptoms of autism, dyslexia or both in their children should consult with a developmental-behavioral pediatrician or other medical professional. Children with autism and dyslexia benefit from early diagnosis and intervention. There are overlaps in these two conditions, which means a professional will need to take the child’s history and any other relevant factors in consideration to make an accurate diagnosis.

References:

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Wagner, R.K. (2018) Why Is It So Difficult to Diagnose Dyslexia and How Can We Do It Better? Florida State University and Florida Center for Reading Research, 7(5) https://dyslexiaida.org/why-is-it-so-difficult-to-diagnose-dyslexia-and-how-can-we-do-it-better/