Subclinical hypomania in youth and bipolar disorder: a phenotypic continuum? A critical review

Bipolar disorder (BD) is characterised by episodes of mania and hypomania (the less severe presentation of mania). (Hypo)manic symptoms include elevated/irritable mood, increased energy, and goal-directed behaviour. Subclinical hypomania is common in non-clinical community populations, particularly among adolescents. Evidence indicates that experiencing these symptoms in youth is linked to the development of BD. However, questions remain around whether subclinical hypomania lies on the same continuum as BD phenotypically and aetiologically and, thus, represents a valid target for its study. This critical review synthesises some of the research surrounding the predictive and construct validity of youth subclinical hypomania as a quantitative trait of BD. The findings presented show that youth subclinical hypomania I) is associated with the later development of BD, and II) shares similarities with BD, including risk factors (high heritability, childhood maltreatment/adversity, substance use), and co-occurring symptoms (depression, psychosis, sleep problems, personality traits) and conditions (substance use, anxiety, personality disorders, attention-deficit/hyperactivity disorder, autism). Despite the sparsity of research and limitations of the literature, these associations are similar to those observed in other well-documented continuums (e.g., autistic traits–autism, psychotic-like experiences–adult psychopathology) and are suggestive of the predictive and construct validity of the youth subclinical hypomania–BD continuum. BD is a multisymptomatic illness that may be best understood as the intersection of various quantitative traits, but youth subclinical hypomania appears to represent one important target for its study. Given its adverse impact and association with other mental illnesses, youth subclinical hypomania warrants investigation in its own right.