Exploring the female autism phenotype of repetitive behaviours and restricted interests (RBRIs): a systematic PRISMA review

Clare Allely (Department of Psychology, University of Salford, Salford, UK)

Advances in Autism

ISSN: 2056-3868

Article publication date: 11 June 2019

Issue publication date: 11 June 2019

Abstract

Purpose

The purpose of this paper is to address the need for increased understanding, awareness and recognition of the autism female phenotype in terms of repetitive behaviours and restricted interests (RBRIs).

Design/methodology/approach

A systematic PRISMA review was conducted. The main aim of the present systematic review is to identify studies which have investigated RBRIs in females with autism spectrum disorder (ASD) or the differences in RBRIs between males and females with ASD.

Findings

In sum, 19 relevant articles were identified: 5 studies found no significant evidence to support the notion of sex differences in RRBIs in ASD; 1 study did not report any differences in RRBIs between males and females with ASD; 12 studies found evidence that males with ASD had significantly more RRBIs compared to females with ASD; and, lastly, 1 study found that girls with ASD have features of RRBIs which are exhibited more compared to boys with ASD.

Research limitations/implications

There is a real lack of in-depth knowledge and understanding of the female phenotype of ASD, and such lack of knowledge has a detrimental impact on the identification of autistic females and a lack of identification can have negative consequence. This is important to address in future research as it is well established that the earlier the diagnosis, the better the outcomes, due to the timely access to appropriate interventions.

Practical implications

The RBRIs exhibited in autistic females are not sufficiently captured by most currently diagnostic instruments. Clinicians are less likely to identify the RBRIs in females as they tend not to be the typical repetitive behaviours commonly associated with ASD. It has been recommended that clinicians consider “females as a whole” in terms of their clinical presentation and look for any indication of RBRIs, even repetitive interests which appear clinically innocuous.

Originality/value

There is relatively little research investigating RBRIs in autistic women and girls. There is a real need to highlight the importance of understanding and recognising how RBRIs can differ between males and females with ASD.

Keywords

Citation

Allely, C. (2019), "Exploring the female autism phenotype of repetitive behaviours and restricted interests (RBRIs): a systematic PRISMA review", Advances in Autism, Vol. 5 No. 3, pp. 171-186. https://doi.org/10.1108/AIA-09-2018-0030

Publisher

:

Emerald Publishing Limited

Copyright © 2019, Emerald Publishing Limited


Autism spectrum disorder (ASD) is a neurodevelopmental condition which is characterised by social communication and social interaction difficulties in addition to restricted, repetitive behaviours or interests (RBRIs) (APA, 2013). There is significant variability in the clinical presentation of the ASD symptomology across individuals even though they all share the same core symptoms (Veselinova, 2014). In the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV, APA, 1994), autistic disorder was considered to be one of four categorical diagnoses that consisted of a group of disorders referred to as pervasive developmental disorders (PDD). As well as autistic disorder, the PDD group comprised Asperger’s disorder, childhood disintegrative disorder, Rett’s disorder and PDD, not otherwise specified (APA, 2013). In the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the subtypes of ASD have been removed (e.g. autistic disorder and Asperger disorder). In the DSM-5, there is now just a single category of ASD. ASD has an early developmental onset of persistent, typically lifelong symptoms. About four males are diagnosed with ASD for every female (e.g. Fombonne, 2009). The possible explanations for this male-to-female ratio remain elusive (Adamou et al., 2018).

Repetitive behaviours and restricted interests (RBRIs): current RRBI diagnostic criteria

RBRIs characterise behaviours that can include repetitive motor movements, sensory reactions, rituals, routines and restricted interests. RBRIs are common during early typical development (e.g. Arnott et al., 2010; Leekam et al., 2007). What makes the RBRIs which can be exhibited in early typical development different from those RBRIs exhibited in autistic individuals is the intensity of these behaviours. A study by South et al. (2005) showed how debilitating RBRIs can be (even in a very high-functioning sample comprising of Asperger’s syndrome and high-functioning autism individuals) with respect to the frequency of occurrence and the level of distress these RBRIs can cause for individuals as well as their families (South et al., 2005). As highlighted above, RBRIs form an essential domain for a diagnosis of ASD (APA, 2013). Moreover, RBRIs have been found to be one of the earliest predictors exhibited in infants of a later diagnosis of ASD (e.g. Ozonoff et al., 2008; Wolff et al., 2014). Research has indicated that there exist two main subtypes of RBRIs (see Leekam et al., 2011). One being repetitive sensory and motor (RSM) behaviours which consist of repetitive motor behaviours and unusual sensory responses, such as simple motor stereotypies and excessive smelling or touching of objects. The other subtype being the insistence on sameness (IS) which includes routines, rigid behaviours and restricted interests (e.g. Bishop et al., 2013; Honey et al., 2012).

For the RBRIs category in the DSM-5 criteria for ASD, there are four symptoms and the individual must exhibit at least two of the four, currently or by history. The four symptoms are:

  1. stereotyped or repetitive motor movements, use of objects or speech (such as simple motor stereotypies, echolalia, repetitive use of objects, lining up toys or flipping objects, or idiosyncratic phrases);

  2. an IS, excessive adherence to routines, ritualised patterns of verbal or nonverbal behaviour, or excessive resistance to change (such as motoric rituals, insistence on same route or food, rigid thinking patterns, repetitive questioning or extreme distress at small changes);

  3. highly restricted, fixated interests that are abnormal in intensity or focus (such as strong attachment to or preoccupation with unusual objects, excessively circumscribed or perseverative interests); and

  4. hyper‐or hypo‐reactivity to sensory input or unusual interest in sensory aspects of environment (such as an apparent indifference to pain/heat/cold, adverse response to specific sounds or textures, excessive smelling or touching of objects, fascination with lights or spinning objects) (see DSM-5, 2013, p. 50).

RBRIs between males and females with ASD

Numerous researchers and clinicians have argued that one of the potential explanations for more males being diagnosed with ASD is that males display more (on average) RBRIs than females. RBRIs are an ASD symptomology which may be recognised more easily (Hartley and Sikora, 2009; van Wijngaarden-Cremers et al., 2014; Zwaigenbaum et al., 2012; Mandy et al., 2012; Koenig and Tsatsanis, 2005; Kreiser and White, 2014; Rivet and Matson, 2011). In females with a higher IQ or with less extreme stereotypies, ASD often goes undetected (e.g. Baird et al., 2011). In the 22 studies that van Wijngaarden-Cremers et al. (2014) included in their meta-analysis, it is possible that autistic females with a higher IQ may have been missed. If this was the case, then the authors argue that the meta-analysis would have overestimated problems in females in the domain of communication, social behaviour and RBRIs restricted interests, which was not the case. Instead, autistic males and females exhibited similar symptom severity on communication and social behaviour. However, autistic girls exhibited less RBRIs compared to autistic boys. In their meta-analysis, van Wijngaarden-Cremers et al. (2014) were not able to include intellectual disability as a confounder because of the lack of specific data on this in the original articles they identified. The key finding from the meta-analysis was that autistic boys exhibited more RBRIs compared to autistic girls. RBRIs are not unique to ASD as they can be found in children with an intellectual disability and severe deprivation and in typically developing children with intelligence, which is within the normal range (Muthugovindan and Singer, 2009).

Limitations with the current RRBI diagnostic criteria

A limitation of the current RRBI diagnostic criteria is that is does not represent the full range of RRBIs types (Mandy et al., 2012). Many autistic females may have very extreme interests or behaviours but in areas which fall out with the “typical” ASD interests (which are so stereotypical and commonly found in ASD males), which would exclude them from fulfilling the criteria for RRBIs for a diagnosis of ASD (Hull et al., 2017). Or they may have interests which are a preoccupation with parts of an object which is less obvious than it is in males, less rituals, routines and stereotypical mannerisms (Nicholas et al., 2008), less factual expertise (e.g. knowledge of subway or train routes) and less oddly formal play (Mandy et al., 2012). An example which clearly demonstrates how the quality of RBRIs may be different in autistic females is a young woman who always carried a number of well-worn books wherever she went. She would constantly read the books at the expense of all social interactions. This may be a type of repetitive behaviour which is not easily identified or recognised as being a circumscribed or “special interest” (Halladay et al., 2015).

Present study

Some studies support the notion that the sex differences appear to emerge only later in development as several studies have found that there are no differences in the behavioural presentation between ASD male and female toddlers (e.g. Reinhardt et al., 2015; Postorino et al., 2015). This suggests that females may learn to mask or camouflage their autistic traits, which would support the female phenotype theory. However, if the difference only emerges later in development, the question this raises is why are girls not diagnosed earlier like boys. However, there are a number of studies which do show differences between autistic boys and girls (e.g. Rynkiewicz et al., 2016). Therefore, to date, the literature on whether there are sex/gender differences in ASD symptomology is inconsistent. The main aim of the present systematic review is to identify studies which have investigated RBRIs in females with ASD or the differences in RBRIs between males and females with ASD.

Methods

A total of five internet-based bibliographic databases were searched in order to identify studies which empirically investigated camouflaging or masking behaviour in females with ASD: specifically, PsycARTICLES Full Text; AMED (Allied and Complementary Medicine) 1985–November 2018; PsycEXTRA 1908–10 December 2018; PsycINFO 2002–December Week 5 2018 and Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily 1946–4 January 2019. The search on the five databases was conducted on 7 January 2019. The search followed PRISMA guidelines (see Liberati et al., 2009; Moher et al., 2009). The search was not restricted by date. Search terms were applied to title. The following search criteria were entered into the five databases: (“repetitive behavio* and restricted interests” or RBRI* or “repetitive/stereotyped behavio* “or RRB* or “restricted and repetitive behavio*” or “restricted, repetitive behavio* and interests” or RRBI* or “restricted and repetitive behavio*” or “stereotypic and repetitive behavio*“ or “repetitive sensory and motor behavio*” or “stereotypic behavio*” or “repetitive and stereotyped behavio*” or “restricted repetitive pattern of interests and behavio*” or “stereotypic/ repetitive movement*” or “motor stereotypies” or “repetitive and/or restricted behavio* and interests”).m_titl. AND (ASD* or “autis* spectrum disorder*” or autis* or “autis* spectrum condition*” or asperger*).m_titl. AND (gender or sex or female* or women or woman or girl*).m_titl.

This search returned a total of nine articles. Following the removal of duplications, there were five articles which were all relevant for the review. As well as the searches carried out on the five databases listed above, a variety of permutations of ASD in relation to female differences in RBRIs were entered into Google Scholar and thoroughly screened for any potentially relevant articles not identified through the database searches. For instance, RBRIs AND female AND autism, “repetitive behaviours” AND autism AND female; “repetitive behaviors” AND autism AND female; gender AND autism AND repetitive; “restricted and repetitive behaviour” AND autism AND female, etc. This resulted in 14 further studies which were identified as being relevant to the present review (see Figure 1 for PRISMA flow diagram of this process). Lastly, because this is a relatively under-researched area within autism research, the decision was made for the present systematic review to adopt an inclusive approach. No exclusion criteria were implemented for the studies identified which have explored RBRIs in females with ASD or the differences in RBRIs between males and females with ASD. All papers published since 2008 will be considered for inclusion in the present review.

Results

A total of 19 articles were identified as relevant to the present review.

Sex differences in RRBIs in ASD

Out of the total of 19 articles, 5 found no significant evidence to support the notion of sex differences in RRBIs in ASD (Solomon et al., 2012; Andersson et al., 2013; Harrop et al., 2015; Reinhardt et al., 2015; Knutsen et al., 2018). It is important to emphasise one of these studies here. The study carried out by Knutsen et al. (2018) revealed more similarities than differences between males and females with ASD in the core diagnostic domain of RBRIs based on clinical observations. However, they did find something interesting. Compared to similar males, younger higher-functioning and older lower-functioning females exhibited reduced rates on the Autism Diagnostic Observation Schedule restricted and repetitive behaviour subcategory unusually repetitive/excessive, stereotyped behaviours. It is important to highlight that this study conducted by Knutsen et al. (2018) uses the biggest known sample to date of 1,024 individually matched female and male children with ASD to investigate sex differences in RRBIs based on clinician observation. One study did not report any differences in RRBIs between males and females with ASD (Chowdhury et al., 2010). However, they only had one female with ASD in their sample and therefore they could not carry out any analysis looking at differences between males and females.

In sum, 12 studies found evidence that males with ASD had significantly more RRBIs compared to females with ASD (Hartley and Sikora, 2009; Bölte et al., 2011; Hattier et al., 2011; Sipes et al., 2011; Mandy et al., 2012; Park et al., 2012; Szatmari et al., 2012; Frazier et al., 2014; Hiller et al., 2014; Wilson et al., 2016; Supekar and Menon, 2015; Dean et al., 2017). Lastly, one study found that girls with ASD have features of RRBIs which are exhibited more compared to boys with ASD (Antezana et al., 2018). Specifically, they found that the items that were found to best-discriminate gender were heightened stereotyped behaviours and restricted interest items in the boys and compulsive, sameness, restricted and self-injurious behaviour items in the girls. This study is the first to find that girls with ASD may have increased compulsive, sameness and restricted RRBI compared to boys (Antezana et al., 2018).

The study conducted by Hiller et al. (2014) is worth pointing out here as it found that girls presented with both less and different restricted interests. A major contribution of this work is its exploration of the specific types of restricted interests displayed by boys and girls. For the 89 per cent of boys and 58 per cent of girls who did present with a fixated interest, the findings indicated that girls and boys present differently in terms of the types of fixations that they have. Specifically, compared to girls, boys were more likely to demonstrate fixated interests with televisions or video games, while girls were more likely to demonstrate interests around random objects. This included animals, rocks, shells or books. Interestingly, when the sample was split into older and younger children, these seemingly random fixations held by many girls, remained the most common category (Hiller et al., 2014). Compared to males, the restricted and repetitive interests among females were thus more difficult to categorise and “identify as atypical” (Hiller et al., 2014, p. 1391). Results supported the finding that, compared to boys, fewer girls with ASD exhibited restricted interests and other behaviours such as lining up or sorting objects (Hartley and Sikora, 2009; Mandy et al., 2012).

The study by Mandy et al. (2012) also revealed differences between males and females with ASD on certain items within the RRBIs domain. They found that, compared to females, males were especially likely to score on items measuring “oddly formal play” involving lining up toys and having “a large store of factual information”. The authors suggest that these are both behaviours which are relevant to the systematising construct which has been advocated by Baron-Cohen (2002). Mandy et al. (2012) go on to suggest that their findings are consistent with Baron-Cohen’s “extreme male brain” theory of ASD which would predict that, even amongst individuals with ASD, males would exhibit higher scores for systemising.

Interestingly, Bölte et al. (2011), in a sample of 35 males and 21 females with higher-functioning ASD and unaffected sibling controls, investigated visual attention to detail (ATTD) and selected executive functions (EF). Based on the Autism Diagnostic Interview-Revised (ADI-R) or the Autism Diagnostic Observation Schedule (ADOS), Bölte et al. (2011) found that EF impairments in males were correlated with more RBRIs. The findings suggested that RBRIs are more pronounced in males compared to females and that the observed association between EF and RBRIs (stereotypic behaviours and interests) is stronger in the autistic males. Autistic females exhibited a better EF which was found to be associated with less RBRIs. The authors state that the “identified association between EF and stereotypic behaviours and interests is indeed a ‘possible’ one” (Bölte et al., 2011, p. 507).

Lastly, it is important to point out here that one study found that the amount of change also differed according to different subtypes of the RRBIs. Chowdhury et al. (2010) investigated age-related changes in RBRIs in 34 high-functioning adults with ASDs at current age and retrospectively at age four to five years using the Autism Diagnostic Interview-Revised and the Repetitive Behaviour Scale-Revised (RBS-R). They found evidence of significant changes in all RBRIs over time, the only exception being the Self-injurious Behaviour subscale of the RBS-R. Chowdhury et al., from childhood to adulthood, found a 75 per cent improvement in compulsions, a 71 per cent improvement in stereotypies and a 53.6 per cent improvement in self-injurious behaviours. They found that about 44 per cent exhibited improvement on the restricted behaviour subscale (44.1 per cent) (Chowdhury et al., 2010).

Neuroanatomical findings

Only one study was identified which used not just clinical judgement, psychological and behavioural assessments, etc., but also neuroanatomical data. Supekar and Menon (2015) analysis of neuroanatomical data revealed, for the first time, that girls and boys with ASD differ in the organisation of cortical and subcortical motor systems and that RRBI severity is associated with sex differences in grey matter (GM) morphometry in distinct motor systems (Supekar and Menon, 2015).

Genetic liability

Another study reported findings which supported the hypothesis of a multiple threshold model of genetic liability of ASD with females having a higher liability for affectation status, at least on the repetitive behaviour dimension of ASD (Szatmari et al., 2012). Szatmari et al.’s (2012) sample included individuals with ASD (970 families, 2,028 individuals) who were recruited as part of the Autism Genome Project. They differentiated the families into families containing a female (either female–female or male–female) and those with only males. Szatmari et al. argued that if the sex with the lower prevalence is associated with a greater genetic liability necessary to cross sex-specific thresholds, the males from female containing families should be more severely affected than males from male only families. Affected subjects from the different types of families with ASD were sampled and compared on the social reciprocity and repetitive behaviour scores from the ADI-R. In general, females were found to have lower repetitive behaviour scores compared to males. Additionally, males from female containing families were found to have higher repetitive behaviour scores when compared to males from male–male families (Szatmari et al., 2012).

Discussion

This review highlighted the lack of consistency across the studies in terms of whether there are sex differences in RBRIs in ASD. The review also highlights the relatively little research attention that has been given to this particular area with only 19 studies being identified. Out of the total of 19 articles, 5 found no significant evidence to support the notion of sex differences in RRBIs in ASD (Solomon et al., 2012; Andersson et al., 2013; Harrop et al., 2015; Reinhardt et al., 2015; Knutsen et al., 2018). It is important to emphasise one of these studies here. Knutsen et al.’s (2018) study revealed more similarities than differences between males and females with ASD in the core diagnostic domain of RBRIs based on clinical observations. One study did not report any differences in RBRIs between males and females with ASD as they only had one female with ASD in their sample. As a result, analysis looking at the difference between males and females with ASD could not be carried out (Chowdhury et al., 2010).

In sum, 12 studies identified in the present review found evidence that males with ASD had significantly more RRBIs compared to females with ASD (Hartley and Sikora, 2009; Bölte et al., 2011; Hattier et al., 2011; Sipes et al., 2011; Mandy et al., 2012; Park et al., 2012; Szatmari et al., 2012; Frazier et al., 2014; Hiller et al., 2014; Wilson et al., 2016; Supekar and Menon, 2015; Dean et al., 2017). Lastly, one study found that girls with ASD have features of RRBIs which are exhibited more compared to boys with ASD (Antezana et al., 2018). Specifically, they found that the items that were found to best-discriminate gender were greater stereotyped behaviours and restricted interests in the boys and compulsive, sameness, restricted and self-injurious behaviour items in the girls (Antezana et al., 2018). Antezana et al. (2018) discuss some of the potential limitations with their study. For instance, the data used in the study was gathered from numerous studies (with few overlapping measures); therefore, specific exclusion/inclusion criteria may impact the ability to generalise from the findings. For instance, IQ data were only available for a subset of the sample. A large age range was adopted in the study, and age differences in RRBI may impact on the findings. As mentioned later, The RBS-R (Bodfish et al., 2000) is a parent-report measure. Therefore, it is subject to bias as a result of the different interpretations that can be made of items and scores assigned by each parent. For example, “pulling hair” could be interpreted a number of ways such as compulsive (i.e. trichotillomania), sensory-based or self-injurious. However, it is important to point out here that this is the first study of its kind as it investigated gender differences in RRBIs using a comprehensive RRBI measure in children with ASD. Only two other studies identified in the present review used the RBS‐R (Chowdhury et al., 2010; Solomon et al., 2012; Frazier et al., 2014).

The results from the study conducted by Knutsen et al. (2018) identified more RRBI similarities than differences between females and males. They had expected that RRBI domain differences would emerge among primary school-aged higher or lower functioning groups. However, this was not found. Such a finding would have been consistent with the findings from other studies (e.g. Szatmari et al., 2012; Supekar and Menon, 2015). The findings by Knutsen et al. are consistent with the findings from earlier studies which found similar RRBI domain scores on clinician-reported diagnostic measures between female and male children with ASD (Andersson et al., 2013; Harrop et al., 2015; Reinhardt et al., 2015).

Four of the five studies identified in the present review which found no significant differences in RBRIs between males and females with ASD overall (Andersson et al., 2013; Harrop et al., 2015; Reinhardt et al., 2015; Knutsen et al., 2018) are inconsistent with the findings from a meta-analysis by van Wijngaarden-Cremers et al. (2014). In their systematic review and meta-analysis of 22 peer reviewed original publications which investigated gender differences in the core triad of impairments in ASD, they observed lower rates of RRBIs in females compared to males aged between 6 and 12 years of age (a similar age range to the samples in the four studies identified in this review which found no significant differences). However, as pointed out by Knutsen et al. (2018) in their paper, the meta-analysis by van Wijngaarden-Cremers et al. (2014) included findings from both clinician (ADOS) and caregiver (ADI-R) report, whereas the study by Knutsen et al. (2018) included a clinical sample which was only based on direct clinical observation (ADOS). Knutsen et al. acknowledge the inherent bias in their sample which only included children who were referred to an autism treatment network (ATN) site. (The ATN registry is the first and one of the largest autism data registries in North America.) Additionally, they highlight the potential issues surrounding direct clinician observation as opposed to relying on historical report (e.g. from the parents) which may be another potential contributory factor resulting in the discrepancies in findings in relation to whether there are differences in RBRIs between males and females with ASD. They highlight that there may be differences between clinical and caregiver perspectives of RRBIs (e.g. Le Couteur et al., 2008; Lemler, 2012; Ventola et al., 2006) and in exclusively female samples (Kopp et al., 2010).

The study by Reinhardt et al. (2015) found no sex differences in relation to RBRIs in males and females with ASD. However, they acknowledge a potential limitation with their study that may explain this. Their sample consisted of 511 children (288 of whom were diagnosed with ASD). However, only 54 females with ASD were included (Reinhardt et al., 2015). A larger sample may have resulted in a stronger significance level between the groups with respect to differences in the amount of RBRIs. Indeed, the issues of underpowered sample sizes are not unique to this particular study. Solomon et al. (2012) examined phenotypic differences between boys and girls based on a sample of 8–18 year old autistic girls (n = 20) and boys (n = 20), and typically developing girls (n = 19) and boys (n = 17). Only marginally significant differences in the domain of RBRIs were reported in this study (Solomon et al., 2012). Such a limitation was emphasised by Mandy et al. (2012) (who did find sex differences in RBRIs in individuals with ASD. They argue that the reason for some of the studies not finding sex differences in RBRIs is likely to be due to their methodological characteristics as opposed to a type I error in their own study. They highlighted examples of earlier studies (published before 2008) where they suggest that their null findings may be due to group comparisons which lack sufficient statistical power in order to detect the moderately sized effects they found (e.g. Carter et al., 2007; Holtmann et al., 2007).

Another important consideration when looking at potential explanations for why some studies may report null findings are the possible differences in growth trajectories that may occur across the life course. Indeed, Harrop et al. (2015) postulated that girls and boys may exhibit differential growth trajectories which change over the course of the lifespan (which was found in the study by Frazier et al., 2014). In their study, they found a trend towards this. However, it was found to be statistically non-significant (which again, may be due to underpowered sample. Their sample comprised of only 29 girls with ASD and 29 boys with ASD) (Harrop et al., 2015), although the study did not find any statistically significant sex difference in the young girls and boys on lower order RRBIs. However, these young boys’ and girls’ RBRI profile may change throughout the lifespan and gender differences may present in older, higher-functioning children with ASD. Differences in growth trajectories across the lifespan was found by Chowdhury et al. (2010) in individuals with ASD as a whole (both males and females). Moreover, Knutsen et al. (2018) found that younger higher-functioning and older lower-functioning females exhibited reduced rates on the Autism Diagnostic Observation Schedule restricted and repetitive behaviour subcategory unusually repetitive/excessive, stereotyped behaviours when compared to similar males. Such findings have obvious clinical and developmental implications for females with ASD (Harrop et al., 2015). Interestingly, Hattier et al. (2011) found that, irrespective of age or gender, the frequency of RRBIs do not appear to change between young adulthood and later adulthood which is consistent will earlier findings by Gillberg and Steffenburg (1987), who argued that there is no discernible trajectory in ASD symptoms. Specifically, they argue that some ASD symptoms may plateau while some others may become more pronounced over time.

The suggestion that there is a higher liability threshold for expression of RBRIs in autistic females is important to consider, given the studies discussed above showing, overall, lower levels of RBRIs in autistic females (particularly in high-functioning females) compared to autistic males. As mentioned earlier, this may be one potential explanation for the very high sex ratios at the high end of the spectrum as RBRIs are considered to be a crucial behavioural symptom for the identification of ASD (Frazier et al., 2014). If repetitive behaviour is used as critical diagnostic criteria, females with ASD will potentially not be identified by existing diagnostic assessments (Rynkiewicz et al., 2016). Mandy et al. (2012) detailed some prospective solutions to this. First, that there could be a lowering of the diagnostic threshold for clinical significance of RBRIs in females. Second, current RBRI scales/measurements could be modified so that they exclude the items with have been found to be sex-biased or, alternatively, creating sex-specific algorithms with differential item weighting, or combining these two recommendations. Before any of these prospective solutions can be put in place, there needs to be much more research in order to further delineate sex differences in ASD (Mandy et al., 2012).

Interestingly, Frazier et al. (2014) also highlighted that this raises the issues of whether high-functioning females who do not exhibit restricted interests but have impairments in the social communication/interaction domain and the need for sameness would meet the diagnostic criteria for social communication (pragmatic) disorder or whether there needs to be a “relaxation” of the DSM-5 criteria for ASD for females. In current diagnostic assessments, symptoms exemplars which are specific to the female phenotype are not explicitly found. Frazier et al. (2014) argued that behaviour exemplars which are specific to the female phenotype need to be included in commonly-used assessment tools. This may result in more females being correctly identified and diagnosed (Frazier et al., 2014). As pointed out by Solomon et al. (2012), sex-specific diagnostic criteria for neuropsychiatric disorders (such as ASD) would be more precise and clinically useful (see Hartung and Widiger, 1998).

Limitations

There are some potential limitations with the present systematic review. Primarily, there is the potential that relevant articles have not been identified in the search carried out on the databases. It is important to note that there are very few papers which have focussed specifically on sex differences in RBRIs in ASD populations. Typically, studies focus on ASD symptoms more broadly and RBRIs is a subgroup analysis. This means that it is challenging to identify all studies which have included analysis of sex differences in RBRIs in populations with ASD because it was not the primary focus of their study and therefore this key wording is not included in the title of the paper for identification in databases searches, etc. However, in order to reduce the risk of this the “Googlescholar” search was carried out in addition to the database search. All relevant papers were reviewed (including reference sections) for the purposes of identifying any potentially relevant articles which were not identified during the database searches. Every attempt was made to ensure that there were no inherent biases in the identification of papers for inclusion in this review.

Clinical implications and recommendations

Clinical considerations when assessing possible RBRIs and avoiding stereotyping

There is need for increased understanding, awareness and recognition of the female phenotype in terms of RBRIs (Wilson et al., 2016; Gould, 2017). The RBRIs exhibited in autistic females are not sufficiently captured by most currently used diagnostic instruments. Moreover, clinicians are less likely to identify the RBRIs in females as they tend not to be the typical repetitive behaviours commonly associated with ASD (Gould, 2017). Clinicians need to be cautious about potentially stereotyping observed behaviours. Identifying the typical types of RBRIs which can be found in both males and females (across the lifespan) is one step forward to address these identified issues (Wilson et al., 2016).

Kreiser and White (2014) recommend that clinicians consider the following questions when assessing a female for possible ASD: “Is there any negative impact on social, academic, or occupational activities as a result of engaging in the activity or interest?” and “What happens when the engagement in the activity or interest is interrupted or stopped?”. Importantly, it is the quality and intensity of these activities or interests, in addition to the amount of time spent engaged with them, that is important to consider as opposed to the special interests (Gould and Ashton-Smith, 2011). It is recommended that clinicians consider “females as a whole” in terms of their clinical presentation and look for any indication of RBRIs, even repetitive interests which appear clinically innocuous. Additionally, so that symptoms can be accurately recognised, clinicians should be encouraged, if they do not do so already, to gain as much clinical experience as possible observing the male and female phenotypes of ASD (Halladay et al., 2015).

Future research directions

First, it is worth pointing out that there is a need for future studies to include females with varying levels of “severity” of ASD symptomology (Bargiela et al., 2016).

Exploring the gender differences on measures of RBRIs in more detail

Autistic females tend to score lower on measures of RBRIs compared to ASD males. However, there is a need for empirical research to explore whether this gender difference is due to actual differences in these traits or if females are scoring lower on the measures because they are “simply” not captured by the measures (Van Wjingaarden-Cremers et al., 2014; Bargiela et al., 2016).

Investigating the clinical utility of the ASSQ-REV in female populations

As mentioned earlier, ASD screening tools have been developed (and therefore normed) based on the male phenotype which questions the validity of these tools for autistic females. In order to investigate this Kopp and Gillberg (2011) identified and evaluated 18 items which are thought to be sensitive to the female phenotype of ASD. These 18 items were integrated into the Autism Spectrum Screening Questionnaire (ASSQ; Ehlers et al., 1999). This instrument was developed to screen for Asperger syndrome and high-functioning autism. Findings revealed that a number of items on the newly named ASSQ-Revised Extended Version (ASSQ-REV) exhibited a higher sensitivity to autistic females. Additionally, there were four questions on the ASSQ-REV which girls would typically provide an affirmative response to, namely, avoiding demands, difficulty completing daily activities due to repetitive behaviours, interacting mostly with younger children, or having a different voice or speech when compared to boys (Kopp and Gillberg, 2011; Haney, 2016). It would be useful to investigate how this tool captures female exemplars of RBRIs across the lifespan – from childhood to adulthood.

Gould has already recommended that current diagnostic instruments and/or manuals need to be adapted to include symptom exemplars which capture the female phenotype of ASD – e.g. the types of RBRIs exhibited in ASD females (Gould, 2017). Future studies could investigate the clinical utility of the new screening tool. the ASSQ-REV (Kopp and Gillberg, 2011), in how sensitive it is to female features of ASD (using samples of girls and women). In their sample, Kopp and Gillberg (2011) found that certain single ASSQ-GIRL items were much more typical of autistic girls compared to autistic boys. The single items which were most marked included: “avoids demands”, “very determined”, “careless with physical appearance and dress” and “interacts mostly with younger children”.

Adapted version of the Repetitive Behaviour Questionnaire-2 (RBQ-2)

It would be useful for future research to investigate the RBRIs in females compared to males using measures specifically designed to investigate this behaviour. One measure that would be worth considering is the RBQ-2 (Leekam et al., 2007; Lidstone et al., 2014) which is a 20-item questionnaire. The items are directly derived from a standardised clinical interview tool, the Diagnostic Interview for Social and Communication Disorders (Wing et al., 2002). Barrett et al. (2015) investigated an adapted version of the RBQ-2. They adapted it into an adult self-report questionnaire which they called the Adult RBQ-2 (RBQ-2A). The authors emphasise that, given that the RBQ-2A has been adapted into a self-report measure, it is only accessible to participants who have sufficient cognitive resources and verbal ability to enable them to complete the questionnaire (Barrett et al., 2015). Their findings indicated that the RBQ-2A has utility as a self-report questionnaire measure of RRBIs for adults (Barrett et al., 2015).

Neurobiological substrates of RBRIs in autistic females compared to ASD males

As pointed out by van Wijngaarden-Cremers et al. (2014), the “male-skewed bias towards restricted interests and behaviors and stereotypes has not been precisely elucidated by biological theories. The underlying mechanisms are yet to be identified” (p. 633). Future studies could investigate this using functional magnetic resonance imaging or other less expensive, relatively motion-tolerant and more transportable measures of neurobiological activity such as functional near-Infrared spectroscopy (fNIRS). fNIRS measures brain activity through the hemodynamic responses associated with neuron behaviour. There is increasing use of fNIRS in autism research (see Mazzoni et al., 2018). Additionally, Supekar and Menon (2015) recommended more research is needed to explore how the observed sex differences in neuroanatomy that they found in their study are associated with current ADI-R RRB scores, current ADI-R RRB subscales scores repetitive, sensory motor behaviours (RSM), IS and circumscribed interests, and/or other measures of RRB including the RBS-R. In their study, Supekar and Menon (2015) studied volume (GM). They suggest that there is a need for further research to explore any sex differences in the cortical surface area and cortical thickness (which are the two components of volume) (Supekar and Menon, 2015).

The role of neuropeptides in RBRIs

Solomon et al. (2012) highlighted in their paper some of the studies which have linked differences in RBRIs and variations in neuropeptides including oxytocin and vasopressin (e.g. Carter, 2007; Hollander et al., 2003; Insel et al., 1999). Moreover, there have been some small-scale studies which have found that infusions of oxytocin reduce RBRIs in adult autistic males (Hollander et al., 2003). More recently, Yang et al. (2015) found that cortisol, serotonin and oxytocin may all have a contributory role in the presentation of RBRIs in autistic individuals. Further research could investigate the role of these neuropeptides in RBRIs in ASD (males and females) across the lifespan and investigate treatment implications for more severe cases (e.g. of particularly extreme self-injurious behaviour such as head banging).

Conclusions

In the present review, only 19 studies were identified which looked at sex differences in RBRIs in males and females with ASD. Also, 12 studies found evidence that males with ASD had significantly more RRBIs compared to females with ASD. This review highlighted the lack of consistency across the studies in terms of whether there are sex differences in RBRIs in ASD with five of the 19 studies finding no statistically significant sex differences. There is a real need to highlight the importance of understanding and recognising how RBRIs can differ between males and females with ASD. This is important to address in future research as it is well established that the earlier the diagnosis, the better the outcomes, due to the timely access to appropriate interventions (Begeer et al., 2013; Mademtzi et al., 2018).

Figures

PRISMA flow diagram

Figure 1

PRISMA flow diagram

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Acknowledgements

Conflicts of interest: the author(s) have no conflicts of interest to declare.

Corresponding author

Dr Clare Allely can be contacted at: c.s.allely@salford.ac.uk

About the author

Dr Clare Allely is Reader in Forensic Psychology at School of Health Sciences, University of Salford, Manchester, England, and Affiliate Member of the Gillberg Neuropsychiatry Centre, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. Clare holds a PhD in Psychology from the University of Manchester and has previously graduated with an MA (Hons) in Psychology from the University of Glasgow, an MRes in Psychological Research Methods from the University of Strathclyde and an MSc in Forensic Psychology from Glasgow Caledonian University. Clare is also Honorary Research Fellow in the College of Medical, Veterinary and Life Sciences affiliated to the Institute of Health and Wellbeing at the University of Glasgow. Clare’s primary research projects and interests include the pathway to intended violence in mass shooters, and serial homicide and autism spectrum disorders in the criminal justice system.