Investigating the Relationship between Autistic Traits, Ruminative Thinking, and Suicidality in a Clinical Sample of Subjects with Bipolar Disorder and Borderline Personality Disorder

(1) Background: Previous literature reported in both subjects with Borderline personality disorder (BPD) and Bipolar disorder (BD) higher levels of autistic traits, linked to a greater suicidality risk. The aim of this study was to evaluate and compare the presence of autistic traits in a sample of individuals with BD or BPD, with a specific focus on suicidality. (2) Methods: We recruited two clinical samples of subjects (BPD and BD) and a control group without a diagnosis according to DSM-5 (CTL). Subjects were assessed with the AdAS Spectrum, the RRS and, for evaluating suicidality, the MOODS-SR. (3) Results: The CTL group showed significantly lower scores of both BD and BPD on AdAS Spectrum, RRS, and suicidality scores. BPD subjects showed significantly lower scores than BD ones in most of AdAS Spectrum domain scores. Correlation and regression analyses highlighted specific patterns of association among AdAS Spectrum domains, RRS, and suicidality in each clinical group. (4) Conclusions: Both BPD and BD individuals show greater levels of autistic traits, which seem to be distributed in a continuum featuring the highest levels among BD subjects. In both disorders, higher autistic traits were linked to suicidal tendencies, although with different patterns of association between BD and BPD subjects.