Neurodivergence encompasses neurodevelopmental conditions including autism, attention-deficit hyperactivity disorder (ADHD) and Tourette syndrome. Particular physical traits, notably those linked to joint hypermobility, have an established association with both neurodivergence and bipolar affective disorder.

This case-control study tested, first, whether the presence of joint hypermobility predicted bipolar affective disorder and, secondly, whether neurodivergent characteristics were important in understanding this relationship.

Data were collected from 52 participants with self-reported clinical diagnoses of bipolar affective disorder and from a comparison group of 54 participants without diagnosis of bipolar affective disorder. All participants were assessed on screening instruments for autism (Ritvo Autism Asperger Diagnostic Scale; RAADS-R), ADHD (Wender Utah Rating Scale; WURS) and joint hypermobility. Group differences were explored, and odds ratios calculated for the presence of bipolar and neurodivergence given the presence of hypermobility. A mediation analysis was performed to determine the contribution of neurodivergent characteristics to the relationship between joint hypermobility and bipolar affective disorder.

The presence of joint hypermobility significantly predicted the presence of bipolar disorder (odds ratio 5.1; 95% CI = 2.1, 12.4). In the bipolar affective disorder group, the prevalence of likely autism and ADHD was greater (84.6 and 65.4% respectively) than in the comparison group (22.2 and 3.7% respectively). The odds ratio for a diagnosis of bipolar affective disorder was 18.2 (95% CI = (6.70, 49.41)) in those meeting the threshold for likely autism; and 46.89 (95% CI = 9.96, 220.74) in participants meeting the threshold for likely ADHD. Mediation analysis showed that autistic, ADHD and pooled neurodivergent characteristics mediated the link between joint hypermobility and bipolar affective disorder.

This suggests a potential mechanism for affective pathophysiology, through developmental characteristics associated with joint hypermobility. The appreciation of interacting physical and neurodivergent traits to the expression of psychiatric illness has implications for diagnostic formulation, personalised medicine and service design.