This study examines the clinical and familial correlates of bipolar disorder (BPD) when it occurs with and without autism spectrum disorders (ASD) comorbidity in a well characterized research referred population of youth with BPD. We hypothesized that in youth with BPD the clinical and familial correlates of BPD will be comparable irrespective of the comorbidity with ASD.

Clinical correlates and familial risk was assessed using data from a large family study of youth with bipolar I disorder (BPD-I; probands N = 157; relatives N = 487). Findings in BPD-I youth were compared with those of youth with ADHD without BPD-I (probands N = 162; relatives N = 511) and age and sex matched controls without BPD-I or ADHD (probands N = 136; relatives N = 411). All subjects were comprehensively assessed using structured diagnostic interviews and a wide range of non overlapping measures assessing multiple dimensions of functioning.

Thirty percent (47/155) of the BPD-I probands met criteria for ASD. The age at onset of BPD was significantly earlier in the presence of ASD comorbidity (4.7±2.9 vs. 6.3±3.7 years; p = 0.01). The phenotypic and familial correlates of BPD were similar in youth with and without ASD comorbidity.

A clinically significant minority of youth with BPD-I suffers from comorbid ASD. Phenotypic and familial correlates of BPD were typical of the disorder in the presence of ASD comorbidity. BPD-I comorbidity with ASD represents a very severe psychopathologic state in youth.