## 6 Discussion: The Critical Role of Twin Studies in Examining the Association Between CDS and ED  
ED is increasingly recognized as a transdiagnostic factor present across a wide range of psychological conditions [7], including internalizing and externalizing disorders [8], as well as neurodevelopmental disorders such as ADHD [37]. Given the well-documented comorbidity between CDS, internalizing disorders, externalizing disorders, and ADHD [4], it is crucial to explore the relationship between CDS and ED. Understanding this relationship could provide valuable insights into the distinct and shared mechanisms underlying these conditions and inform tailored intervention strategies. Twin studies offer a particularly valuable approach for disentangling genetic and environmental contributions to this relationship, helping to clarify the role of ED in the co-occurrence of these conditions and its potential as a shared underlying mechanism. However, despite growing interest, the interplay between CDS and ED remains relatively underexplored, particularly in terms of their etiological underpinnings and developmental trajectories. One probable factor contributing to this knowledge gap is the conceptual ambiguity surrounding both CDS and ED [4,75]. Specifically, ED lacks a universally accepted and comprehensive definition, leading researchers to focus on its individual components--such as ER strategies, emotional impulsivity, and emotional ability--rather than addressing its multidimensional nature in a systematic manner [76]. Similarly, there is ongoing debate regarding the nosological status of CDS, with some scholars arguing that it constitutes a distinct clinical entity, while others contend that it represents a phenotypic variation within the broader ADHD spectrum [75]. Emerging theoretical frameworks and empirical findings suggest that certain neurodevelopmental and psychiatric comorbidities may not represent discrete disorders but rather alternative phenotypic expressions of ADHD [75]. This raises critical questions regarding the conceptualization of overlapping clinical phenomena and whether they should be integrated into an expanded ADHD framework. Notably, ER difficulties and CDS are among the most frequently proposed domains within this broader ADHD characterization [75]. Furthermore, empirical evidence indicates a significant association between ED and CDS, underscoring the need for further research into the etiopathogenice mechanisms underlying their co-occurrence [4]. ED has been increasingly acknowledged as a critical aspect of EF, with deficits in EF commonly observed in individuals with CDS [31,49]. Research suggests that ED may mediate the relationship between CDS and various psychopathological outcomes, particularly Internalizing and Externalizing symptoms [74]. However, understanding how ED operates within this context, especially in relation to developmental trajectories, requires further investigation. Twin studies offer a valuable framework for exploring these mediating mechanisms [44]. By examining the interplay between CDS, ED, and EF through twin designs, gaining a more comprehensive understanding of how ED interacts within the broader spectrum of CDS and its role in the development of psychopathological symptoms would be possible. Nevertheless, the relationship between CDS and ED throughout development remains poorly understood, as do the developmental trajectories and potential age-related variations in this association. A more comprehensive understanding of the interplay between these two phenotypes is essential, as it would enable further investigation into the etiological basis of the CDS-ED relationship and provide insights into its longitudinal trajectories. This, in turn, could facilitate a more precise characterization of neurodevelopmental and psychiatric conditions and inform targeted intervention strategies.