Dlgap2 突變小鼠作為自閉症類群障礙模型之重複行為、社會互動與同理心分析

Abstract

自閉症光譜障礙（Autism Spectrum Disorder, ASD）是一種神經發展性疾病，其核心特徵包括社交溝通缺陷、侷限且重複的行為模式，以及同理心功能異常。近年來，ASD盛行率持續上升。根據美國疾病管制與預防中心（CDC）統計，目前約每36名兒童中即有1名被診斷為ASD，且男性診斷率約為女性的4.2倍。儘管ASD具有顯著的臨床與社會影響，其致病機制仍未完全釐清，因此有必要透過動物模型進行系統性的行為與神經機制研究。 本研究所使用之Dlgap2突變小鼠模型源自一名台大醫院ASD男童，其基因分析顯示第8號染色體短臂末端存在約2.4 Mb缺失區域，其中涵蓋Dlgap2基因。Dlgap2為突觸後支架蛋白，在興奮性突觸結構維持與訊號傳遞中扮演關鍵角色，並被認為與ASD病理機制密切相關。 基於此模型，我們系統性分析Dlgap2基因劑量對ASD相關行為與神經活化之影響，聚焦於互惠社交行為、重複性行為與同理心相關行為。整體結果顯示，Dlgap2缺失導致顯著且具基因型依賴性的行為改變與神經活動異常，揭示基因劑量與表型之間呈現非線性關係。更重要的是，完全缺失（KO）與部分缺失（Het）並非僅代表嚴重度差異，而是形成兩種不同的行為狀態，反映不同神經調控機制的參與。 在行為層面，KO小鼠呈現較明顯的社交資訊處理與行為模式異常，其社交探索雖增加，但互動模式非典型，並在不同壓力情境下表現重複性行為的刻板化傾向。相較之下，Het小鼠則主要呈現情緒與壓力調控層面的隱性異常，包括焦慮樣行為增加、情境依賴性的自我梳理行為上升，以及同理／安撫相關行為下降，顯示其社交行為表現雖大致保留，但情緒調節與行為輸出轉換能力出現明顯異常。 從神經機制角度觀察，KO小鼠的行為異常可能與社交線索編碼受損導致的訊息失真有關；而Het小鼠則可能反映前扣帶皮質（ACC）過度活化所引發的情緒感染增強，但行為輸出未能有效轉譯為適應性社交反應，反而偏向以自我導向的重複性行為作為壓力調節策略。 值得注意的是，本研究首次在Het小鼠辨識出ASD相關行為表型，其基因狀態更貼近臨床常見的雜合突變型態，突顯Dlgap2模型的轉譯價值。同時，不同於多數研究將社交與重複性行為分開分析，本研究顯示Het小鼠的重複性行為具有明顯情境依賴性，主要出現在社交情境中，提供重新理解ASD行為模式的重要線索。此外，同理心相關缺陷僅出現在Het小鼠中，顯示即使部分Dlgap2功能喪失亦足以干擾社交與情緒處理；相對地，KO小鼠仍保有較完整同理心表現，可能反映完全缺失下所啟動的補償性神經機制，提示不同基因劑量透過不同適應性路徑導致行為分化。 由以上實驗結果，我們確認Dlgap2基因劑量在ASD行為表型與神經活化模式的塑造中扮演關鍵角色，並提供理解同理心相關神經迴路的重要實驗證據。本研究建立更精細的ASD動物行為分析框架，亦為釐清ASD神經機制與未來診斷及治療策略發展奠定基礎。

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication, restricted and repetitive behavioral patterns, and impairments in empathic processing. In recent years, the prevalence of ASD has continued to rise. According to statistics from the Centers for Disease Control and Prevention (CDC), approximately 1 in 36 children is diagnosed with ASD, with a male diagnosis rate approximately 4.2 times higher than that of females. Although ASD has substantial clinical and social impacts, its underlying pathogenic mechanisms remain incompletely understood; therefore, systematic investigations of behavioral and neural mechanisms using animal models are necessary. The Dlgap2 mutant mouse model used in this study was derived from an ASD male child at National Taiwan University Hospital, whose genetic analysis revealed an approximately 2.4 Mb deletion at the terminal region of chromosome 8p, encompassing the Dlgap2 gene. Dlgap2 is a postsynaptic scaffolding protein that plays a critical role in maintaining excitatory synaptic structure and signal transmission and is considered to be closely associated with the pathophysiological mechanisms of ASD. Based on this model, we systematically analyzed the effects of Dlgap2 gene dosage on ASD-related behaviors and neural activity, focusing on reciprocal social behavior, repetitive behavior, and empathy-related behavior. Overall, the results show that Dlgap2 deficiency leads to significant and genotype-dependent behavioral changes and neural activity abnormalities, revealing a non-linear relationship between gene dosage and phenotype. More importantly, complete loss (KO) and partial loss (Het) do not merely represent differences in severity; they constitute two distinct behavioral states, reflecting the involvement of distinct neural regulatory mechanisms. At the behavioral level, KO mice exhibited more pronounced abnormalities in social information processing and behavioral organization, with increased social exploration but atypical interaction patterns, and showed stereotyped repetitive behaviors across different stress conditions. In contrast, Het mice primarily exhibited subtle abnormalities in emotional and stress regulation, including increased anxiety-like behavior, context-dependent increases in self-grooming, and reduced empathic/comforting-related behaviors, indicating that although their social behavior is largely preserved, emotional regulation and behavioral output transformation abilities are significantly impaired. From a neuromechanistic perspective, the behavioral abnormalities in KO mice may be associated with impaired encoding of social cues leading to distorted information processing; whereas in Het mice, they may reflect enhanced emotional contagion driven by hyperactivation of the anterior cingulate cortex (ACC), but with failure to translate behavioral output into adaptive social responses, instead biasing toward self-directed repetitive behavior as a stress-regulatory strategy. Notably, this study identified ASD-related behavioral phenotypes in Het mice for the first time, and their genetic state more closely resembles the heterozygous mutations commonly observed in clinical ASD cases, highlighting the translational value of the Dlgap2 model. At the same time, unlike most studies that analyze social and repetitive behaviors separately, this study shows that repetitive behavior in Het mice is strongly context-dependent and mainly emerges in social contexts, providing important insights for reinterpreting ASD behavioral patterns. In addition, empathy-related deficits were observed only in Het mice, indicating that even partial loss of Dlgap2 function is sufficient to disrupt social and emotional processing; in contrast, KO mice retained relatively intact empathic behavior, which may reflect compensatory neural mechanisms activated under complete loss, suggesting that different gene dosages lead to behavioral divergence through distinct adaptive pathways. From the above experimental results, we confirm that Dlgap2 gene dosage plays a critical role in shaping ASD behavioral phenotypes and neural activation patterns, and provides important experimental evidence for understanding empathy-related neural circuits. This study establishes a more refined behavioral analysis framework for ASD animal models and lays a foundation for elucidating ASD neurobiological mechanisms and the development of future diagnostic and therapeutic strategies.