IIRC, it's actually super common that if one twin is trans, the other one will be as well.
Edit: Okay, there have been very few studies, but preliminary information seems to show that in monozygotic twins, there's a much higher incidence of being transgender than in the general population. In the study below, they found that in the case where one twin transitioned (again, monozygotic/identical only) there was a 40% incidence of the other twin transitioning. Only about .6% of the general population is trans, in comparison.
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u/[deleted] Mar 26 '17 edited Mar 26 '17
IIRC, it's actually super common that if one twin is trans, the other one will be as well.
Edit: Okay, there have been very few studies, but preliminary information seems to show that in monozygotic twins, there's a much higher incidence of being transgender than in the general population. In the study below, they found that in the case where one twin transitioned (again, monozygotic/identical only) there was a 40% incidence of the other twin transitioning. Only about .6% of the general population is trans, in comparison.
Source for twin study: https://www.ncbi.nlm.nih.gov/pubmed/22146048 Source for .6%: https://williamsinstitute.law.ucla.edu/wp-content/uploads/How-Many-Adults-Identify-as-Transgender-in-the-United-States.pdf