The Aberrant Behavior Checklist for Fragile X Syndrome: A Qualitative Clinician Evaluation of Content Validity

<b><i>Objective:</i></b> The current intense period of drug development for fragile X syndrome (FXS) and other neurodevelopmental disorders (NDDs) indications has highlighted the importance of behavioral outcome measures with strong psychometric properties and specifically content validity. The Aberrant Behavior Checklist-Community Edition (ABC-C), which has successfully been applied to autism spectrum disorder drug trials, has been revised for FXS (ABC_FX) and is widely used for both clinical and research purposes. Despite its strong psychometric validation, the ABC_FX and its parent measure have not been subjected to qualitative content validity evaluations. The present study intended to fill this gap. <b><i>Methods:</i></b> Using two surveys administered sequentially and developed with guidance and review from the Food and Drug Administration (FDA), we asked 10 clinicians experienced in FXS and related NDDs to determine the adequacy of the ABC_FX for assessing its behavioral constructs, its relevance to FXS, and its potential for detecting response to interventions. Various descriptive statistic parameters and <i>ad hoc</i> metrics were used to analyze categorical and Likert-like scale responses. <b><i>Results:</i></b> Experts considered that most items and all six ABC_FX subscales indeed evaluated their explicit or implicit behavioral constructs. However, item and subscale specificity were relatively low (∼25%-30%). Relevance of items of the Hyperactivity subscale was relatively high while low for many items of the Socially Unresponsive/Lethargic subscale. These items were also considered of low responsiveness potential. Irritability, Hyperactivity, Stereotypy, and Social Avoidance were the subscales with the strongest profiles, although the experts estimated that Stereotypy items may not be that responsive to treatment. A novel Anxiety construct, representing mainly recently reported observable behaviors, contributed mainly by Irritability items, emerged as a potential measure. <b><i>Conclusions:</i></b> The present study demonstrated the overall adequacy of the ABC_FX for its behavioral constructs, its relevance to FXS, and its potential for detecting response to treatment. It also showed that anxiety, a distinctive feature of FXS and other genetic NDDs, can also be measured by the ABC_FX. These findings can help with the implementation and interpretation of the ABC_FX, as well as with potential improvements to the measure in FXS and other NDDs.