Comorbidity Between Hikikomori and Autistic Traits May Be Identified as a Phenotypical Presentation Characterized by Greater Severity

<b>Objectives</b>: Hikikomori is a condition characterized by extreme social withdrawal, functional impairment, and mental distress, which has gained increasing recognition worldwide. While it can be associated with comorbid psychiatric disorders, hikikomori shares similarities with autism spectrum, prompting investigations into their relationship. Given that hikikomori commonly manifests in early adulthood, this study aimed to explore the relationship between autistic features and hikikomori tendencies among university students. <b>Methods</b>: A total of 2037 university students were recruited via an online survey and assessed with the Adult Autism Subthreshold (AdAS) Spectrum and the Hikikomori Questionnaire (HQ-25). Participants were categorized into four groups: healthy controls (HCs), subjects with hikikomori tendencies (HKs), subjects with significant autistic traits (ATs), and subjects with both significant ATs and hikikomori tendencies (AT-HKs). <b>Results</b>: Results showed significant effects of both hikikomori presence and significant ATs on AdAS Spectrum and HQ-25 scores, while a significant effect of their interaction was detected on AdAS Spectrum scores. The AT-HK group consistently scored higher on both AdAS Spectrum and HQ-25 compared to other groups, with the AT and HK groups outperforming HCs in specific domains. HQ-25 Socialization and Isolation domains predicted higher AdAS Spectrum scores in hikikomori subjects, while various AdAS Spectrum domains served as predictors of HQ-25 scores in AT subjects. <b>Conclusions</b>: This study highlights a significant relationship between ATs and hikikomori tendencies in university students, suggesting that their comorbidity may represent a more severe phenotype, where each condition may exacerbate the other.