Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) are two distinct neurodevelopmental conditions. However, they frequently co-occur, with many individuals diagnosed with both. Even if not diagnosed with both, there is a considerable overlap between them resulting in many shared behaviours. This overlap has gained increasing attention as research reveals shared characteristics and neurological causality.
The Prevalence of Co-Occurrence
Studies indicate significant overlap between ASD and ADHD, with estimates suggesting that 30-50% of individuals with ASD also have ADHD (Leitner, 2014). Similarly, between 20-50% of individuals with ADHD display traits associated with autism (Kerns et al., 2016). Recognising this dual presence, the 2013 DSM-5 revised its guidelines to allow a dual diagnosis of ASD and ADHD (American Psychiatric Association, 2013). This change reflects growing recognition of the overlap, with many individuals now identifying with AuDHD, indicating that they experience traits of both conditions.
Shared Characteristics and Symptoms
ASD and ADHD share several characteristics, which can complicate diagnosis. Both conditions may involve difficulties with social interaction, communication, and emotional regulation, though they present differently:
- Social Challenges: Individuals with ASD often have challenges reading social cues and understanding norms, while those with ADHD might struggle socially due to impulsivity and inattentiveness, sometimes leading to missed cues and perceived disinterest (Antshel & Russo, 2019).
- Attention and Focus: ADHD is marked by distractibility, whereas ASD may involve intense focus on specific interests, often referred to as monotropism in autism literature. This type of focus is similar to ADHD’s hyperfocus, and can also result in similar attention challenges to ADHD, blurring diagnostic distinctions (Polderman et al., 2014).
- Sensory Sensitivities: While sensory processing issues are commonly linked to ASD, individuals with ADHD also frequently report them. Sensory sensitivities, such as reactivity to sounds or lights, can lead to distractibility and challenges in focus for both groups (Groom et al., 2017).
Neurological and Genetic Factors
Research suggests ASD and ADHD share genetic and neurological components, which may explain their co-occurrence. Both conditions involve atypical functioning in brain areas tied to attention, social behaviour, and executive functioning (Rommelse et al., 2010). Genetic studies reveal overlapping markers, particularly in genes related to dopamine regulation and synaptic development, which influence attention and impulse control (Faraone & Larsson, 2019). These shared features contribute to diagnostic complexity, and the term AuDHD has emerged to capture this combined experience.
Why Many People Are Diagnosed with Both Conditions
The diagnostic overlap between ASD and ADHD can be attributed to shared symptoms and neurological characteristics. Many symptoms, like sensory processing issues or hyperfocus, appear similar, leading clinicians to assess both conditions. Key factors that increase the likelihood of a dual diagnosis include:
- Diagnostic Criteria and Symptom Presentation: Hyperactivity and impulsivity in ADHD can manifest as repetitive or focused behaviours in ASD, making symptoms appear similar (Leitner, 2014).
- Late or Misdiagnosis: Often, individuals may receive a diagnosis for one condition initially, with traits of the other emerging over time. A person might be diagnosed with ADHD in childhood but later assessed for ASD as they show additional traits (Antshel & Russo, 2019).
- Genetic ‘Risk’ Factors: ASD and ADHD share genetic markers, increasing the likelihood of a dual diagnosis in individuals with a family history of either condition (Faraone & Larsson, 2019). Please note, genetic risk factors is the official terminology, which should be reviewed as seeing either condition as a ‘risk’ ignore the positive attributes of both.
- Environmental and Developmental Influences: Factors like early social experiences or educational settings can influence symptom presentation (how it manifests, not whether the condition is present in the first place), sometimes revealing traits of both ASD and ADHD over time (Rommelse et al., 2010).
Venn Diagram of ADHD, ASD, and AuDHD
The below Venn diagram, credit to Megan Anna Neff of Neurodivergent Insights, provides a good visualisation of the common overlaps and distinctions.
References
Rommelse, N. N., et al. (2010). “Shared heritability of attention-deficit/hyperactivity disorder and autism spectrum disorder.” European Child & Adolescent Psychiatry, 19(3), 281-295.
American Psychiatric Association. (2013). Diagnostic and Statistical Manual of Mental Disorders (5th ed.). APA.
Antshel, K. M., & Russo, N. (2019). “ADHD and the Comorbidity Spectrum: Current Research on ADHD and Co-Occurring Conditions.” Clinical Psychology Review.
Faraone, S. V., & Larsson, H. (2019). “Genetics of Attention Deficit Hyperactivity Disorder.” Molecular Psychiatry, 24(4), 562-575.
Groom, M. J., et al. (2017). “The overlapping neurodevelopmental continuum in ADHD and autism spectrum disorder.” British Journal of Psychiatry, 210(6), 499-501.
Kerns, C. M., et al. (2016). “The Overlap and Distinction Between ASD and ADHD in Early Childhood: What We Know About Co-occurrence and Shared Characteristics.” Clinical Child and Family Psychology Review, 19(2), 77-107.
Leitner, Y. (2014). “The Co-Occurrence of Autism and Attention Deficit Hyperactivity Disorder in Children: What Do We Know?” Frontiers in Human Neuroscience, 8, 268.
Mulligan, A., et al. (2009). “Genetic Contributions to ADHD Symptomatology in ASD.” Journal of the American Academy of Child and Adolescent Psychiatry, 48(7), 719-727.
Polderman, T. J. C., et al. (2014). “The Shared Genetic Architecture of Attention-Deficit/Hyperactivity Disorder and Autism Spectrum Disorder.” Psychological Medicine, 44(12), 2537-2546.
Neff, M. A., (n.d.) “Is it ADHD or Autism? (Or Both)” Neurodivergent Insights, neurodivergentinsights.com/misdiagnosis-monday/adhd-vs-autism