Discussion

The findings of this study align with existing literature highlighting the complex intersection between autism and co-occurring mental health conditions. Autism, defined as a neurodevelopmental condition characterised by difficulties in social interaction and communication, as well as restrictive and repetitive behaviours, ¹ is often underdiagnosed or diagnosed late because of barriers such as limited public awareness, lack of service availability, and funding constraints. ^{Reference Micai, Fulceri, Salvitti, Romano, Poustka and Diehm2} This is concerning, given estimates suggesting that 1.1% of the UK population meets criteria for ASD, with similar global prevalence rates. ^{Reference Zeidan, Fombonne, Scorah, Ibrahim, Durkin and Saxena3}

There is growing recognition that autistic individuals are at significantly higher risk for developing a range of mental health conditions, including obsessive–compulsive disorder, bipolar disorder, depression, psychosis, anxiety and eating disorders. ^{Reference Eberhard, Billstedt and Gillberg4,Reference Lai, Kassee, Besney, Bonato, Hull and Mandy5,Reference Hirvikoski, Mittendorfer-Rutz, Boman, Larsson and Lichtenstein16} Alarmingly, research has found that autistic individuals are also at increased risk for suicidality, with suicide attempts and deaths occurring at roughly twice the rate of the general population. ^{Reference Hossain, Khan, Sultana, Ma, McKyer and Ahmed17,Reference Hartley18} Life stressors, social isolation and perceived burdensomeness have been identified as contributing factors. ^{Reference Hirvikoski, Mittendorfer-Rutz, Boman, Larsson, Lichtenstein and Bölte6} In addition, the high prevalence of anxiety (up to 42%) and depression (37%) in autistic individuals has been linked to exacerbation of core ASD traits and increased risk of self-harm. ^{Reference Wood, Drahota, Sze, Har, Chiu and Langer7,Reference Gajwani and Minnis8}

This cohort demonstrates no differences in the type or frequency of mental health diagnoses between autistic males and females. Despite the increased ratio of males/females, very few studies have explored the differences in mental health diagnoses between the two sexes. One study demonstrated autistic males were more likely to have a diagnosis of ADHD, but less likely to have bipolar disorder or schizophrenia. ^{Reference Gaetano13} A previous large population-based cohort demonstrated that females are particularly more likely to develop anxiety, sleep or depressive disorders when compared with autistic males. ^{Reference Hirvikoski, Mittendorfer-Rutz, Boman, Larsson and Lichtenstein16} However, although the women in our study had higher rates of an eating disorder, anxiety and self-harm, this was not statistically significant. This may be a result of the relatively small sample size in our cohort. This potentially has implication in service delivery and support needed for these groups.

This study highlights that autistic people have high rates of mental health conditions. This reiterates previous research that demonstrated increased rates of eating disorders, anxiety, psychosis and obsessive–compulsive disorder. For instance, a previous large population cohort found that both male and female autistic individuals were three times more likely to develop a mental health condition and were significantly more likely to be admitted to hospital. ^{Reference Hirvikoski, Mittendorfer-Rutz, Boman, Larsson and Lichtenstein16} Furthermore, there is an increased risk of suicide, self-harm and suicidal thoughts. Potential explanations for this include the increased risk of traumatic life experiences such as isolation, victimisation and perceived burdensomeness. Not only do these experiences occur more frequently when someone is autistic, but they increase the risk of mental health conditions, which can also further perpetuate these experiences. ^{Reference Douglas and Sedgewick19–Reference Cage, Di Monaco and Newell21} Mental health conditions can also amplify some of the behaviours associated with autism, such as social difficulties, repetitive behaviours and sensory challenges.

The present study also found that prenatal exposure to substances, especially alcohol and postnatal trauma, is more common among autistic people, in this sample. This double effect, where neurological vulnerability is compounded by external traumatic experiences such as victimisation, unemployment or abuse, ^{Reference Martini, Butwicka and Taylor15} emphasises the need to consider both aspects in the presentation of autistic individuals when they present to mental health services.

Rates of trauma reported by this cohort seem surprisingly low and reasons for this are unclear. As data relied on retrospective examination of case notes it may be that incidents of previous trauma were not documented in full for all of the people in this sample. It may also be that memories of past traumatic events are subject to recall bias.

Limitations of this study include small sample size and clinical population, reducing the generalisation to the wider population and low statistical power. It is also possible that there may have been overcorrection by using a correction approach in some cases, suggesting a possible type two error because of the size of that sample. The cohort in this study were presenting for diagnostic assessment for autism as adults and had waited a long time to be seen, and this may have had implications for how they presented. Having to live as someone with unrecognised autism may also have contributed to poor mental health for some of these people. ^{Reference Gellini and Marczak22,Reference Bitsika and Sharpley23} The study did not collect data on sex differences with trauma, although a recent study suggests that there may not be sex differences in the prevalence of traumatic stress in young people. ^{Reference Tamilson, Eccles and Shaw24}