What is the neurological basis for the association between Bipolar type 2 and autism spectrum disorder (ASD)? Bipolar disorder type 2 and autism spectrum disorder (ASD) is regularly seen together. What is the neurological explanation for this?
Google Scholar identifies several learned articles that discuss the association/overlap between bipolar disorder type 2 and autism spectrum disorder (ASD), including:

Khanzada, N. S., Butler, M. G., &amp; Manzardo, A. M. (2017). GeneAnalytics pathway analysis and genetic overlap among autism spectrum disorder, bipolar disorder and schizophrenia. International Journal of Molecular Sciences, 18(3), 527. https://doi.org/10.3390/ijms18030527

Stahlberg, O., Soderstrom, H., Rastam, M., &amp; Gillberg, C. (2004). Bipolar disorder, schizophrenia, and other psychotic disorders in adults with childhood onset AD/HD and/or autism spectrum disorders. Journal of neural transmission, 111(7), 891-902. https://doi.org/10.1007/s00702-004-0115-1

Gandal, M. J., Zhang, P., Hadjimichael, E., Walker, R. L., Chen, C., Liu, S., ... &amp; Shieh, A. W. (2018). Transcriptome-wide isoform-level dysregulation in ASD, schizophrenia, and bipolar disorder. Science, 362(6420). https://doi.org/10.1126/science.aat8127


Excerpts from the above include:

The conditions show similar neuropsychiatric behavioral disturbances, including impaired social interaction and communication.


Twenty-three genes were common to all three disorders.


Overlapping genes impacted dopamine and serotonin homeostasis and signal transduction pathways, impacting mood, behavior and physical activity level.

My non-expert interpretation of the above is that there are genetic processes at work that drive the similarities in behaviour associated with these conditions.