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This summary highlights key findings, but the full paper offers a deeper exploration of depression in autistic individuals. Access the complete paper for a comprehensive discussion of diagnostic challenges, clinical implications, and research directions.

Autistic characteristics can overlap with symptoms of various mental health conditions, such as difficulties with sleeping, eating, or engaging socially. Considerable research into how autistic people experience anxiety and PTSD has led to the recognition of unique presentations in autism (Kerns et al., 2014; Rumball et al., 2020). Yet, our understanding of how depression presents in autistic adults remains less clear. Although some reviews (Stewart et al., 2006) suggest that depression may present differently in autistic people, comprehensive reviews synthesising these findings with standard diagnostic criteria are lacking. Such a review could help clarify if and how reported symptoms of depression among autistic individuals vary from established diagnostic criteria.

This study aims to fill this gap with a systematic literature review, evaluating research findings against the current diagnostic criteria. This approach serves to:

Review Key Points

1. Diagnostic Challenges

• Overlap of Symptoms: Autistic characteristics, such as an increased need for routine, sensory sensitivities, or reduced social engagement, can be mistaken for depressive symptoms, complicating accurate diagnosis.

• Misinterpretation of Symptoms: Self-reports often focus on internal emotional states, while informant reports (e.g., from caregivers) focus on observable behaviours, leading to discrepancies in how symptoms are perceived and reported.

• Use of Standardised Tools: Diagnostic tools and questionnaires developed for non-autistic populations may fail to capture the specific ways depression presents in autistic individuals, often using language or metaphors that are not easily understood or applicable.

• Irritability and Depression: Irritability was identified as a common experience across autistic individuals of all ages and intellectual abilities, yet the DSM-5-TR primarily associates irritability with younger populations. The review highlights the need to reconsider how irritability is understood in relation to depression in autistic people.

2. Clinical Implications

• Need for Tailored Diagnostic Tools: There is an urgent need for depression diagnostic tools specifically designed for autistic individuals to improve accuracy and treatment.

• Impact of Alexithymia: Difficulty identifying and expressing emotions (alexithymia) can affect how autistic individuals communicate depressive symptoms, necessitating an awareness of communication differences in clinical assessments.

• Personalised Guidelines: Tools like "Know Your Normal" could provide guidance on comparing personal norms with mental health symptoms to improve diagnostic accuracy.

3. Future Research Directions

• Differentiating Symptoms: Future research should clarify whether unique presentations in autistic individuals are due to their autistic characteristics, interactions between autism and depression, or direct manifestations of depression itself.

• Symptom Expression Variability: The expression of depressive symptoms, such as anhedonia or depressed mood, may vary in autistic individuals and needs to be studied further to ensure diagnostic tools represent these experiences and expressions.

• Suicidal Ideation: Limited research exists on the relationship between irritability and suicidal ideation in autistic individuals, highlighting the need for further exploration in this area.

• Co-occurring Conditions: Anxiety frequently co-occurs with depression and can precede or intensify depressive episodes, further complicating diagnosis. The overlap between depression and anxiety needs more focused research.

4. Methodological Concerns

• Data Collection Methods: Clinical interviews may provide detailed symptom descriptions but can introduce interviewer bias, while standardised questionnaires offer consistency but may lack the depth needed to represent complex emotional states.

• Small Sample Sizes and Non-Validated Tools: Many studies use small samples and tools not validated for autistic individuals, affecting the reliability and generalisability of findings.

• Need for Multi-Informant Approaches: Multi-informant reports (self and informant) are necessary for a comprehensive understanding of depressive symptoms. They represent both internal emotional states and observable behaviours.