# Heritability of Bipolar I vs II
**URL:** https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500
**Category:** Factual Questions
**Created:** [March 9, 2021, 5:10am UTC](https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500 "2021-03-09T05:10:29Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)
#### Post date: [March 9, 2021, 5:10am UTC](https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500/1 "2021-03-09T05:10:29Z")
I don’t know if anyone knows, or at least is better at me than Googling.
Bipolar disorder has subtypes I, II, and cyclothymia. They seem to be related in cause but have different symptoms. We know that these disorders are highly genetic, and someone with bipolar has a higher chance of having children with symptoms. My question is: does someone with Bipolar I have a chance of both I and II offspring (and vice versa)? Or does I beget I and so on?
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [March 9, 2021, 7:04pm UTC](https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500/2 "2021-03-09T19:04:35Z")
> **[The Genetics of Bipolar Disorder](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/)**
>
> Bipolar disorder is a mood disorder characterized by impairing episodes of mania and depression. Twin studies have established that bipolar disorder is among the most heritable of medical disorders and efforts to identify specific susceptibility...
> [@](#):
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> Family studies also suggest that bipolar I and II are at least partly genetically distinct: the risk of bipolar II disorder is higher among relatives of patients with bipolar II than among relatives of patients with bipolar I disorder ([Gershon et al., 1982](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/#R35), [Andreasen et al., 1987](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/#R2), [Heun and Maier, 1993](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/#R49)), although in some studies risk of bipolar I is also elevated in relatives of bipolar II probands, suggesting that these mood disorders are not completely etiologically distinct ([Smoller and Finn, 2003](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/#R110)). Taken together, the data suggest that bipolar II is a heterogeneous entity in which some cases are more closely related to bipolar I, some to MDD, and others may represent a genetically distinct disorder that breeds true ([Smoller and Finn, 2003](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637882/#R110)).
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### Author:  [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)
#### Post date: [March 9, 2021, 7:06pm UTC](https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500/3 "2021-03-09T19:06:42Z")
Thanks, I’ll give it a look.
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [March 9, 2021, 7:35pm UTC](https://boards.straightdope.com/t/heritability-of-bipolar-i-vs-ii/937500/4 "2021-03-09T19:35:51Z")
I was surprised at the answer. I had thought that they would be more different phenotypes of the same pool of genotypes but apparently not.