Irritability is a common and impairing clinical presentation in children and adolescents. Despite its significant public health impact, irritability remains an elusive construct. Chronic and severe irritability is the primary symptom of the new DSM-5 diagnosis, disruptive mood dysregulation disorder (DMDD). However, empirical and clinical approaches to irritability are in their relative infancy, and questions regarding the validity of the DMDD diagnosis have been raised. Moreover, irritability is a trait distributed continuously in youth, thereby fitting within the National Institute of Mental Health Research Domain Criteria initiative. Thus, there are opportunities for scientific review and integration. Accordingly, the goals of this review include (a) clarifying the definitions of irritability, incorporating clinical and translational animal work; (b) reviewing the historical context surrounding the study of irritability; (c) reviewing the prevalence, clinical correlates, and longitudinal course of irritability; (d) presenting behavioral and neurobiological findings associated with irritability; and (e) exploring treatment options and proposing future directions for research.

Research has revealed facial emotion labeling deficits in children and adolescents with bipolar disorder. To assess whether such impairments may be an endophenotype for bipolar disorder, the authors examined facial emotion identification proficiency in children who were at risk for bipolar disorder because they had a first-degree relative with the illness. The facial expressions subtests of the Diagnostic Analysis of Nonverbal Accuracy scale were administered to 52 patients with bipolar disorder, 24 at-risk youths, and 78 control subjects, all 4-18 years of age. Compared with the control group, both the bipolar and at-risk groups made more errors identifying facial emotions. The number of errors did not differ significantly between the bipolar and at-risk groups. Deficits in facial emotion labeling may be a risk marker for bipolar disorder. Further study is needed to determine the neural mechanisms involved, as well as to explore other emotional processing impairments in youths at risk for bipolar disorder and to identify genetic associations.