Callous unemotional traits (CUT) are described as stable characteristics in children and adolescents with conduct disorders (CD), and the presence of these traits has been associated with more aggressive and persistent manifestations across life span (^{Frick & White, 2008}). CUT denomination was modified to help reduce the stigma associated with this name, and it is now known as Limited Prosocial Emotions (LPE). LPE characteristics appear to identify an etiologically distinct group of children and adolescents with CD who are at a heightened risk for future maladjustment (^{Colins, Fanti, & Andershed, 2021}).

The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; ^{APA, 2013}) included LPE as a specifier for CD. The eleventh version of the International Classification of Diseases (ICD-11; ^{WHO, 2019}) incorporated it as a specifier for CD as well as for oppositional defiant disorder (ODD). It should be noted that this specifier requires the presence of at least two of four characteristics to establish the diagnosis: lack of empathy, lack of guilt, lack of interest in performance, and shallow/deficient affect.

The convenience of its use in both CD and ODD has been extensively discussed, particularly due to high comorbidity between both diagnoses. Being able to detect children or adolescents most at risk of exhibiting these traits is fundamental in order to prioritize the youths most in need of targeted interventions. To that end, research has established that this specifier can help to distinguish youth with a particularly severe and persistent pattern of dysfunctional behaviors (^{Frick, Ray, Thornton, & Kahn, 2014}). However, the DSM has shown inconsistencies in the authorization of this comorbidity, because at first it was not allowed in the DSM-IV, but it was later approved for its use in the DSM-5. Also, research that relied on rating scales triggered the incorporation of the categorical specifier in DSM-5 relied on dimensional CU scores (^{Frick & White, 2008}), or alternative categorical approaches that helped to identify children and adolescents with both elevated and low levels of CU traits (^{Schwenck et al., 2012}). Consequently, it seems that in the future LPE might be allowed to be employed alongside other* disruptive behavior disorders in new versions of the DSM.

Even more, LPE have also been recognized outside of disruptive behavior disorders. They have been found in patients with neurodevelopmental disorders such as autism spectrum disorder and attention deficit hyperactivity disorder, as well as in patients with anxiety, mood, and substance use disorders (^{Herpers, Rommelse, Bons, Buitelaar, & Scheepers, 2012}).

In addition, LPE have been described in both clinical and community populations. In community samples, 10% to 32% with CD and 2% to 7% without CD fit for LPE, while in clinical samples, 21% to 50% with CD and 14% to 32% without CD met criteria for LPE. Teachers, unlike the children-adolescents or parents, reported the greatest presence of LPE (^{Kahn, Frick, Youngstrom, Findling, & Youngstrom, 2012}).

Even though the construct is more widely identified in males, a study that enrolled 118 adolescent girls found that 26% to 37% of the participants with CD met criteria for the LPE specifier symptom threshold (CD + LPE; ^{Colins & Andershed, 2015}). In regard to its consistency, an investigation which enrolled 811 Spanish children (55% boys) found on two occasions (i.e., end of first and second grades) that mothers, fathers, primary teachers, and ancillary teachers that rated the CU/LPE symptoms showed more trait consistency than occasion-specificity for mothers and fathers, slightly more occasion-specificity than trait consistency for primary teachers, and much more occasion-specificity than trait consistency for ancillary teachers. Also, convergent validity for trait consistency was strong for fathers with mothers but weaker for primary with ancillary teachers, and there was no convergent validity for either trait consistency or occasion-specificity across home and school settings. Thus, CU/LPE symptom ratings within this age range represent a more trait-like construct for mothers and fathers and more state-like construct for primary teachers and ancillary teachers (^{Seijas et al., 2019}).

Notably, an analysis comparing the impact of chronic anger/irritability and LPE in a 10-year follow-up study of 203 youth living in institutions showed that these two traits tended to be stable, but only chronic anger/irritability predicted more externalizing behaviors/adjustment problems 10 years later (^{Urben et al., 2022}), which raises questions about the continuity of LPE as a predictor of disruptive behaviors in youth.

Concerning the use of psychometric tools, there have been many attempts to standardize their use with this specifier. One of these is the Inventory of Callous Unemotional Traits (ICU), which has been one of the most used instruments for the recognition of LPE in pediatric population. However it has several limitations at identifying of the four elements included in the DSM-5 and the ICD-11. For example, a recent meta-analysis (^{Ray & Frick, 2018}) showed that both the ICU parent and child-adolescent versions may only identify two factors in a significant way: insensitivity and indifference, but not shallow or deficient emotions. Given these limitations of the ICU, the Kiddie Schedule for Affective Disorders and Schizophrenia Present and Life Version (K-SADS-PL-5) included the LPE according to DSM-5 criteria (^{de la Peña et al., 2018}).

Of great significance, the Latin American version of this interview has recognized LPE as a transdiagnostic specifier not limited to CD or ODD. The detailed analysis of the four characteristics of LPE within the group of Latin American children and adolescents evaluated with the K-SADS-PL-5 allowed us to establish, through a latent classes analysis, core characteristics (lack of empathy and shallow of deficient affect), that are always present when the complete specifier was integrated, as well as ancillary characteristics (lack of guilt and lack of interest in performance) present or not when the complete specifier was integrated or when only one characteristic was present (^{de la Peña, Rosetti, Palacio, Palacios-Cruz, & Ulloa, 2022}). This can be compared with a recent analysis done in Belgian children in which the authors proposed an alternative model based on theory for the ICU which supports a second order model with three first order factors (Lack of Conscience, Unconcern about Performance, Lack of Emotional Expression), a second order latent factor (General Dimension of CU traits), and a methodological factor encompassing negatively worded items (^{Payot, Monseur, & Stievenart, 2022}).

All in all, more research and different forms of analysis are needed to fully understand this specifier. In a recent exploratory study conducted at the Adolescent Clinic of the Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz (^{Gatica Hernández, 2019}), studied 92 outpatient adolescents (51% males; 15.3 years old; SD = 1.37). Participants were assessed using the K-SADS-PL-5 to confirm LPE; 27.2% and 14.1% of male and female fit respectively into the specifier. Remarkably, 20.7% of those with LPE had at least one disruptive behavior disorder, while 23.9% of those with LPE integrated an anxiety or depressive disorder.

In summary, broadly speaking, research on this specifier can offer useful insights. First and foremost, it would appear that LPE could be detected outside of disruptive behavior disorders and the presence of each characteristic may have a different meaning. Secondly, self-reports by parents or clinicians’ assessment is a challenge to the full recognition of such a construct and needs to be taken into consideration when doing research. Consequently, it is possible that an integral assessment with different raters and instruments will provide a rational way to ratify LPE as a solid specifier. Thirdly, we have now more evidence to consider this condition as a general transdiagnostic specifier in child and adolescent psychiatry. Finally, to have the most informative designs, future research should examine the broad construct to glean a better understanding of LPE and CD. Further research should continue to examine sequencing and external correlates at the component level and to evaluate the incremental value of the multicomponent model of LPE to help us better understand how each component may facilitate our knowledge of the types and severity of disruptive behavioral disorders exhibited by youth (^{Salekin, 2022}).