## 3 Emotional Regulation, Dysregulation, and Twin Studies  
### Emotional Regulation and Emotional Dysregulation: Definitions and Comorbidities  
Emotion Regulation (ER) refers to the set of processes through which individuals influence the onset, intensity, duration, and expression of emotional states to adapt to environmental demands and internal goals [25; 26]. According to [PERSON] process model of ER [26; 27], regulation strategies are categorized based on when they intervene in the emotion-generative process. Antecedent-focused strategies, such as Cognitive Reappraisal, modify the interpretation of a situation before the emotional response is fully generated. In contrast, response-focused strategies, such as Emotion Suppression, attempt to alter the expression of emotion after it has already been elicited [28; 29]. Empirical findings suggest that Cognitive Reappraisal is generally associated with more adaptive outcomes, such as increased positive affect and lower levels of psychopathology, while Emotion Suppression is often linked to heightened physiological stress responses, negative affect, and impaired social functioning. However, a growing body of research emphasizes the need for contextual flexibility in the use of ER strategies [25]. In this view, neither reappraisal nor suppression is inherently adaptive or maladaptive; rather, it is the ability to flexibly shift between strategies in response to changing contexts that determines emotional well-being. Moreover, ER and Executive Functions (EF)--which include processes such as inhibitory control, cognitive flexibility, and working memory--are strongly interrelated. These domains co-develop during childhood and adolescence and support adaptive goal-directed behavior [30]. While some studies suggest that ER scaffolds the development of EF, others propose a bidirectional relationship [31; 32]. For example, children with better ER capacities in early development often show more efficient EF later on, whereas those with poor EF are less capable of implementing effective ER strategies. This dynamic interplay may be particularly relevant for understanding emotion-cognition interactions in neurodevelopmental conditions. Difficulties in Emotion Regulation can lead to a condition known as Emotional Dysregulation (ED), which refers to a persistent pattern of emotional experiences that interfere with an individual's ability to maintain goal-directed behavior and interpersonal functioning [7; 33]. ED is characterized by several core features: heightened emotional sensitivity, intense and prolonged emotional responses, difficulty returning to baseline after an emotional reaction, and an overall lack of regulatory control. Common manifestations include irritability, mood instability, emotional lability, low frustration tolerance, and aggressive outbursts [7; 33]. ED is not merely a transient difficulty but represents a pervasive dysfunction that affects multiple domains of functioning. It has been consistently associated with impaired academic performance, interpersonal difficulties, and a higher risk of psychiatric comorbidities [34; 35; 36]. Individuals with ED are more likely to experience peer rejection, family conflict, and difficulties forming and maintaining social relationships. These disruptions often contribute to a negative feedback loop, where social and environmental stressors further compromise regulatory abilities. Importantly, ED is increasingly recognized as a transdiagnostic construct, meaning that it plays a central role across a wide range of mental health conditions rather than being confined to a specific diagnosis. Historically, ED was viewed primarily in relation to externalizing disorders like ADHD and oppositional defiant disorders, or internalizing disorders such as anxiety and depression. However, mounting evidence indicates that ED contributes broadly to the development, maintenance, and severity of both types of psychopathology [8; 37]. For instance, [PERSON] et al.