**1. Introduction**

Individuals with Down syndrome (DS) are commonly described as socially engaged [1] and as having relatively strong nonverbal social functioning in early childhood [2]. Nevertheless, individuals with DS also experience challenges with core aspects of social relatedness including social cognition, expressive language, and social interaction [3–5]. Social challenges are further evident in rates of co-occurring autism spectrum disorder (ASD) in DS. Recent studies show that approximately 15–18% of children with DS also have an ASD diagnosis, which is markedly higher than the 1% reported in the general population [6,7]. Children with DS, with and without co-occurring ASD, experience social challenges that impede interactions with peers [5,8]. These social difficulties lead to greater potential for social isolation that, in turn, impacts mental health outcomes for this population [9], making social cognition and other social skills potential targets for intervention.

Social cognition is defined as the understanding of other's intentions, emotions, and behaviors [9–11]. This includes concepts such as theory of mind, which is the ability to reason about another's point of view, and affect recognition, the ability to identify emotions in others. Social cognition requires individuals to process and interpret social cues, and these skills impact the selection of social responses and subsequent quality of interactions with others in social contexts [12]. In children with ASD, specific connections have been made between social information processing and social behavior [12,13]. In children with DS, theory of mind performance is a greater relative challenge compared with children with other neurogenetic syndromes and intellectual disabilities, and their performance falls

**Citation:** Schworer, E.K.; Hoffman, E.K.; Esbensen, A.J. Psychometric Evaluation of Social Cognition and Behavior Measures in Children and Adolescents with Down Syndrome. *Brain Sci.* **2021**, *11*, 836. https:// doi.org/10.3390/brainsci11070836

Academic Editors: James Kilner and Antonio Narzisi

Received: 17 May 2021 Accepted: 22 June 2021 Published: 24 June 2021

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below their overall nonverbal cognitive abilities [14,15]. Affect and emotion recognition is also an area of challenge in DS in comparison with children with typical development matched on cognitive or receptive language level [16,17]. Studies using the Social Responsiveness Scale, Second Edition (SRS-2) [18] describe social communication and interactions in individuals with DS at low risk for ASD and show that these individuals have relative strengths in social motivation and challenges with social cognition, communication, and awareness [5,19]. For a review of social cognition development in DS, see [20].

A variety of measures have been used in past social cognition research in DS. Most of these measures are laboratory-based and include false belief tasks involving the location of objects [15,21,22] or the content of a container [15], appearance reality tasks [15,22], and emotion-matching tasks [16,17,23]. Although the majority of research on social cognition is completed with toddlers and preschool-aged children [9], these measures are used in the assessment of older children, adolescents, and young adults with DS [14,15]. Beyond the use of laboratory-based measures, standardized clinical assessments of social cognition have been used successfully to describe performance in other clinical populations such as ASD and Attention-Deficit/Hyperactivity Disorder (ADHD) [24,25]. However, standardized clinical assessments have yet to be evaluated to assess social cognition in DS. Another measure used to assess social cognition, among other social behaviors, is the SRS-2, and previous work supports its utility in 6- to 21-year-olds with DS [5,19]. A benefit of using the SRS-2 is that the parent reports on the child's typical social behavior without the child having to do more intensive in-person assessments. The SRS-2 is reported to have high internal consistency and concurrent validity with other ASD screeners among children with DS [19]; however, broader examination of test-retest reliability, practice effects, and convergent validity with direct assessments of social cognition has yet to be studied.

As we learn more about the social phenotype of children with DS and DS+ASD and as social challenges are better characterized [8,19], additional socially focused interventions tailored to children with DS will be needed. Pilot interventions targeting theory of mind skills have recently been completed with children and adolescents with DS [26] and suggest that these skills can be improved with targeted behavioral intervention. Because of the prospective growth of studies focused on social cognition and interaction in DS, a necessary first step to intervention studies is to validate social cognition and social behavior measures for this population.

Further, the priority to evaluate outcome measures for interventions and clinical trials in DS was expressed by the 2015 National Institutes of Health Down Syndrome Outcome Measure working group [27,28]. A summary from this working group identified no direct assessments of social cognition with evidence for use in DS but did state that the SRS-2 showed promise based on the sensitivity of the measure to detect ASD symptoms in DS [19,28]. Social cognition measures have been psychometrically evaluated in the general population [29–31]; however, continued efforts are needed to determine appropriate measures for DS. Psychometrically evaluating social cognition and social behavior measures in DS will ensure that assessments of these domains are suitable for children with DS and that there are no unintended floor effects due to the behavioral phenotype associated with DS. This psychometric validation is especially important for these measures as previous studies report expressive language artifacts in assessments of social cognition [21].
