The Shared Etiology of Obsessive-Compulsive Behavior and Autistic Repetitive Behavior

Abstract

Autism and OCD phenotypes frequently co-occur, are genetically related to each other, and may share etiological mechanisms. I present evidence to support the hypothesis that autistic repetitive behavior and obsessive compulsive disorder are essentially "synonymous", with autistic persons showing frequent intrusive thoughts, obsessions, and compulsive behavior beyond behaviors traditionally associated with autism (e.g., need for routine), and persons with OCD showing need for sameness, repetitive motor behavior, sensory hypersensitivity, and attention to detail. This hypothesis is tested and supported via factor analysis.

The co occurrence of Autism, OCD, and their symptoms

Over seven studies assessing psychiatric comorbidity in autistic children, the combined prevalence of OCD is 24.4%; over two studies assessing psychiatric comorbidity in autistic adults, the combined prevalence of OCD is 18.8% [Table 1]. The prevalence of OCD in the general population of children is 1-3% (Walitza et al. 2011), and 0.5-0.9% in adults (Adam et al. 2012), meaning OCD occurs around 8-24 times more frequently in autistic children, and 21-38 times more frequently in autistic adults. 

Table 1

Study in children	OCD/Total sample	Study in adults	OCD/Total Sample
Leyfer et al. (2006)	35/94	Hofvander et al. (2009)	29/122
Gjevik et al. (2011)	7/71	Lugnegard et al. (2011)	4/54
Bruin et al. (2006)	6/94
Joshi et al. (2010)	53/217
Van steensel et al. (2012)	3/40
Brookman-Frazee et al. (2018)	19/201
Amr et al. (2011)	33/60
Total Prevalence	183/750 (24.4%)	Total Prevalence	33/176 (18.8%)

In addition to the increased prevalence of met criteria for OCD in autism, autistic persons show high levels of obsessions and compulsions, one study finding the most prevalent obsession being contamination (60%) and the most common compulsion being checking (60%) (Russell et al. 2005). Another study found that autistic persons reported moderate degrees of obsessions and intrusive thoughts (although to a lesser degree than OCD patients) and high levels of compulsions comparable to OCD patients (McDougle et al. 1995). Zandt et al. (2006) replicated this finding.

Autistic traits are highly prevalent in OCD as well (Ivarsson & Melin 2008). Zandt et al. (2006) found that patients with OCD reported equivalent levels of need for sameness, repetitive movements, and repetitive language (e.g., echolalia) to patients with autism. Sensory hypersensitivity, an autistic phenotype, has also been found to high degrees in patients with OCD (Rieke & Anderson 2009)(Lewin et al. 2015), and is correlated with obsessive compulsive symptoms (Dar et al. 2012)(Ben-Sasson et al. 2017). Repetitive movement has also been found in patients with OCD (Harris et al. 2007)(Zandt et al. 2006), as well as insistence on sameness (Zandt et al. 2006)(Abramson et al. 2005). 

While patients with OCD are high in the repetitive domain of autistic traits, the effect for the social domain is quite smaller. Fontenelle et al. (2009) found that compared to controls, persons with OCD do not meaningfully lower on perspective taking (d=0.13), however autistic persons score much lower than controls (d=1.54) (Rogers et al. 2006). Persons with OCD score higher on the autism quotient than controls, however score lower than autistic persons, the autism quotient mainly quantifying social deficits (Wikramanayake et al. 2018). 

Autistic repetitive behavior and OCD are also linked genetically. Children with autistic relatives with high levels of repetitive behavior are significantly more likely to have parents with OCD or OCD symptoms than those with low levels (Hollander et al. 2002). This finding was replicated by Abramson et al. (2005). 

Overall, OCD and autism seem to overlap almost perfectly in the repetitive behavior domain of autistic traits, but not nearly as much in the social domain

Neural & autonomic arousal, repetitive behavior, and OCD

Autism has been called an “intense world syndrome” due to autism involving hyper-excitable neurons, and excessive autonomic arousal, shown by sensory sensitivity, anxiety, etc. (Markram et al. 2007). Repetitive behavior in autism is believed to protect against intense anxiety and distress, and to control the autonomic nervous system (Hirstein et al. 2001)(Markram et al. 2007). Insistence on sameness and repetitive movement are both highly correlated with anxiety (Wigham et al. 2015)(Hwang et al. 2019). 

Tic disorders commonly co-occur with autism (Canitano & Vivanti 2007), and tics are largely underpinned by excessive autonomic arousal (Nagai et al. 2009). Autistic traits are common in tourette's syndrome, one type of tic disorder, repetitive behavior being increased far more than other autistic traits (Darrow et al. 2018). Using the autism quotient, tics are saliently associated with routines, attention switching, and attention to detail, whereas the association with social skills and imagination are much smaller (Huisman-van Dijk et al. 2016). 

Obsessive compulsive behavior and obsessive compulsive disorder are frequent in tourette's syndrome (Grad et al. 1983)(Gaze et al. 2006), and tics are correlated with obsessive compulsive symptoms (Huisman-van Dijk et al. 2016). Likewise, tics are common in obsessive compulsive disorder, and some children diagnosed with OCD go on to develop tourette’s syndrome (Leonard et al. 1992). 

Hyperactivity in the autonomic nervous system has been seen in OCD in response to a patient's triggers, which likely is what provokes anxiety, and compulsions to relieve this anxiety (Simon et al. 2013). The amygdala in OCD is also hyper-reactive to triggers (Simon et al. 2014), which has also been found in autism in response to sensory stimuli (Green et al. 2014). In autism, repetitive behaviors are often used to cope with sensory hyper-reactivity and excessive arousal (Wigham et al. 2015)(Hirstein et al. 2001), and in this sense are essentially compulsions triggered by overstimulation. 

Testing

To test the hypothesis that obsessive compulsive disorder, and autistic repetitive behavior are two aspects of a similar underlying phenotype of repetitive, compulsive behavior, I conducted an online survey with PsyToolkit (Stoet 2010, 2017). To measure autistic traits, I used the AQ-10 (Allison et al. 2012), with an additional 10 items, 8 of which are designed to measure aspects of repetitive behavior, since the AQ-10 mainly quantifies social deficits, but not repetitive behavior. To measure obsessive compulsive traits, I used the brief obsessive compulsive scale (BCOS) (Bejerot et al. 2014). The total sample consisted of 1122 participants who had fully completed the survey.

Factor analysis at the item level of both scales was used to test the hypothesis. If the hypothesis is correct, the first two rotated factors should be composed of: a factor containing items related to social deficits, and a factor containing items related to repetitive and obsessive-compulsive behavior. If the hypothesis is incorrect, the first two rotated factors would be composed of: a factor with autism related items loading on it, and a factor with obsessive compulsive items loading on it. 

The hypothesis was supported by factor analysis, with obsessive compulsive and autistic repetitive behavior items loading onto the first factor, and items related to social deficits loading on the second factor [Table 2]. These factors were significantly correlated however the correlation was small (r=0.10, p=0.000892). 

Table 2

Item (light blue = obsessive compulsive)	F1	F2
I am worried about dirt, germs, and viruses.	0.41
I wash my hands very often or in a special way to be sure I am not dirty or contaminated.	0.43
I fear that my actions might harm others.	0.33
I fear I will lose control and do something I don’t want to do.	0.47
I have unpleasant, forbidden, or perverse sexual thoughts, images, or impulses that frighten me.	0.39
I must check the stove or other electrical appliances, that I have locked the door, or to make sure things have not disappeared.	0.51
My dirty words, thoughts, and curses directed towards God bother me; I have a fear of offending God.
To prevent something terrible from happening, I must have special thoughts or acts done in a special way.	0.59
I am occupied with morality issues, justice, or what is right or wrong.	0.34
How things are placed or how they are positioned is important to me. It needs to feel “just right".	0.65
I get a compelling urge to put my things in a special order.	0.66
I have a compelling urge to repeat certain actions until it feels “just right.”	0.63
I must follow strong impulses to collect and hoard things.	0.55
I have worries that I look peculiar; I am concerned that something is wrong with my looks.	0.40
I do things that injure my body.	0.36
I often notice small sounds when others do not	0.52
I usually concentrate more on the whole picture, rather than the small details (R)
I find it easy to do more than one thing at once (R)		0.32
If there is an interruption, I can switch back to what I was doing very quickly (R)		0.43
I find it easy to ‘read between the lines’ when someone is talking to me (R)		0.78
I know how to tell if someone listening to me is getting bored (R)		0.68
When I’m reading a story I find it difficult to work out the characters’ intentions		0.54
I like to collect information about categories of things (e.g. types of car, types of bird, types of train, types of plant etc)	0.53
I find it easy to work out what someone is thinking or feeling just by looking at their face (R)		0.74
I find it difficult to work out people’s intentions		0.68
I stick to the technical meaning of words rather than what other people think they mean.		0.44
Unless otherwise specified, I assume that people mean exactly what they say.		0.59
I enjoy looking through catalogues of products to see the details of each product and how it compares to others.	0.45
When I learn about a new category I like to go into detail to understand the small differences between different members of that category.	0.52
If I look at a pile of blue sweaters in a shop that are meant to be identical, I would be able to see differences between them	0.53
I would be the first to hear if there was a fly in the room	0.48
I rock backwards and forwards, or side to side, either when sitting or when standing	0.42	0.31
I make repetitive hand and/or finger movements	0.49
I insist that aspects of daily routine must remain the same	0.51	0.31
I have a special object(s) I like to carry around	0.56
Eigenvalues	6.22	3.95

1. Leyfer et al. (2006) Comorbid Psychiatric Disorders in Children with Autism: Interview Development and Rates of Disorders

2. Gjevik et al. (2011) Kiddie-SADS Reveals High Rates of DSM-IV Disorders in Children and Adolescents with Autism Spectrum Disorders

3. Bruin et al. (2006) High Rates of Psychiatric Co-Morbidity in PDD-NOS

4. Joshi et al. (2010) The Heavy Burden of Psychiatric Comorbidity in Youth with Autism Spectrum Disorders: A Large Comparative Study of a Psychiatrically Referred Population

5. Hofvander et al. (2009) Psychiatric and psychosocial problems in adults with normal-intelligence autism spectrum disorders

6. Van steensel et al. (2012) Psychiatric Comorbidity in Children with Autism Spectrum Disorders: A Comparison with Children with ADHD

7. Lugnegard et al. (2011) Psychiatric comorbidity in young adults with a clinical diagnosis of Asperger syndrome

8. Brookman-Frazee et al. (2018) Characterizing psychiatric comorbidity in children with autism spectrum disorder receiving publicly funded mental health services

9. Amr et al. (2011) Comorbid psychiatric disorders in Arab children with Autism spectrum disorders

10. Walitza et al. (2011) Obsessive-Compulsive Disorder in Children and Adolescents

11. Adam et al. (2012) Obsessive–compulsive disorder in the community: 12-month prevalence, comorbidity and impairment

12. Russell et al. (2005) Obsessions and compulsions in Asperger syndrome and high-functioning autism and high-functioning autism

13. McDougle et al. (1995) A Case-Controlled Study of Repetitive Thoughts and Behavior in Adults With Autistic Disorder and Obsessive-Compulsive Disorder

14. Zandt et al. (2006) Repetitive Behaviour in Children with High Functioning Autism and Obsessive Compulsive Disorder

15. Rieke & Anderson (2009) Adolescent/adult sensory profile and obsessive-compulsive disorder.

16. Dar et al. (2012) The relationship between sensory processing, childhood rituals and obsessive–compulsive symptoms

17. Ben-Sasson et al. (2017) Sensory over responsivity and obsessive compulsive symptoms: A cluster analysis

18. Lewin et al. (2015) Sensory Over-Responsivity in Pediatric Obsessive Compulsive Disorder

19. Harris et al. (2007) Nonautistic Motor Stereotypies: Clinical Features and Longitudinal Follow-Up

20. Abramson et al. (2005) The Relationship Between Restrictive and Repetitive Behaviors in Individuals with Autism and Obsessive Compulsive Symptoms in Parents

21. Rogers et al. (2006) Who Cares? Revisiting Empathy in Asperger Syndrome

22. Fontenelle et al. (2009) Empathy and symptoms dimensions of patients with obsessive–compulsive disorder

23. Wikramanayake et al. (2018) Autism spectrum disorders in adult outpatients with obsessive compulsive disorder in the UK

24. Stewart et al. (2017) Elevated Autism Spectrum Disorder Traits in Young Children with OCD

25. Markram et al. (2007) The Intense World Syndrome – an alternative hypothesis for autism

26. Hirstein et al. (2001) Autonomic responses of autistic children to people and objects

27. Wigham et al. (2015) The interplay between sensory processing abnormalities, intolerance of uncertainty, anxiety and restricted and repetitive behaviours in autism spectrum disorder

28. Hwang et al. (2019) Understanding anxiety in adults on the autism spectrum: An investigation of its relationship with intolerance of uncertainty, sensory sensitivities and repetitive behaviours

29. Nagai et al. (2009) Influence of sympathetic autonomic arousal on tics: Implications for a therapeutic behavioral intervention for Tourette syndrome

30. Canitano & Vivanti (2007) Tics and Tourette syndrome in autism spectrum disorders

31. Darrow et al. (2018) Autism Spectrum Symptoms in a Tourette Syndrome Sample

32. Huisman-van Dijk et al. (2016) The relationship between tics, OC, ADHD and autism symptoms: A cross-disorder symptom analysis in Gilles de la Tourette syndrome patients and their family members

33. Grad et al. (1983) Obsessive-Compulsive Symptomatology in Children with Tourette's Syndrome

34. Gaze et al. (2006) Co-occurring Psychiatric Disorders in Children and Adolescents With Tourette Syndrome

35. Leonard et al. (1992) Tics and Tourette's disorder: a 2-to 7-year follow-up of 54 obsessive-compulsive children

36. Simon et al. (2013) Autonomic responses and neural-cardiac coupling during individually tailored symptom provocation in obsessive-compulsive disorder

37. Simon et al. (2014) Amygdala hyperactivation during symptom provocation in obsessive–compulsive disorder and its modulation by distraction

38. Green et al. (2014) Over-Reactive Brain Responses to Sensory Stimuli in Youth With Autism Spectrum Disorders RH: fMRI Response to Sensory Stimuli in ASD

39. Stoet (2010). PsyToolkit - A software package for programming psychological experiments using Linux.

40. Stoet (2017). PsyToolkit: A novel web-based method for running online questionnaires and reaction-time experiments

41. Allison et al. (2012) Toward brief “Red Flags” for autism screening: The Short Autism Spectrum Quotient and the Short Quantitative Checklist for Autism in toddlers in 1,000 cases and 3,000 controls [corrected]

42. Bejerot et al. (2014) The Brief Obsessive-Compulsive Scale (BOCS): A self-report scale for OCD and obsessive-compulsive related disorders

43. Hollander et al. (2002) Obsessive–compulsive behaviors in parents of multiplex autism families

44. Abramson et al. (2005) The Relationship Between Restrictive and Repetitive Behaviors in Individuals with Autism and Obsessive Compulsive Symptoms in Parents