It is difficult to estimate the size of the transgender population, given the diversity within this group, including the fact that many individuals do not seek care from specialised centres.[2]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th edition (DSM-5). Washington, DC: American Psychiatric Publishing; 2022.[10]Collin L, Reisner SL, Tangpricha V, et al. Prevalence of transgender depends on the "case" definition: a systematic review. J Sex Med. 2016 Apr;13(4):613-26.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4823815
For both those assigned male and those assigned female at birth, prevalence is estimated to be <0.1%.[2]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th edition (DSM-5). Washington, DC: American Psychiatric Publishing; 2022. This figure is based on gender-affirming treatment-seeking populations, and is therefore likely to be an underestimation.[2]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th edition (DSM-5). Washington, DC: American Psychiatric Publishing; 2022. According to (anonymous) UK census data from 2021, around 0.5% of the population disclosed that their gender identity and sex registered at birth were different.[11]UK Parliament. 2021 census: what do we know about the LGBT+ population? 16 Jan 2023 [internet publication].
https://commonslibrary.parliament.uk/2021-census-what-do-we-know-about-the-lgbt-population/#:~:text=Around%20262%2C000%20people%20(0.5%25),identity%20as%20'trans%20woman
Some observations suggest children and adults with gender incongruence and gender dysphoria show more features of autism spectrum disorder than the general population.[12]Van Der Miesen AI, Hurley H, De Vries AL. Gender dysphoria and autism spectrum disorder: a narrative review. Int Rev Psychiatry. 2016;28(1):70-80.
http://www.tandfonline.com/doi/full/10.3109/09540261.2015.1111199
http://www.ncbi.nlm.nih.gov/pubmed/26753812?tool=bestpractice.com
[13]Glidden D, Bouman WP, Jones BA, et al. Gender dysphoria and autism spectrum disorder: a systematic review of the literature. Sex Med Rev. 2016 Jan;4(1):3-14.
http://www.ncbi.nlm.nih.gov/pubmed/27872002?tool=bestpractice.com
Gender incongruence and dysphoria may be associated with intersex, genetic, or sex chromosome abnormalities. These should not be assumed to be causative, and their presence rarely alters clinical management.
As a group, transgender people experience an increased risk of general mental health issues, including depression, anxiety, post-traumatic stress disorder, suicidality, and substance use disorders.[1]World Health Organization. International statistical classification of diseases and health related problems (ICD). 11th revision. Jan 2022 [Internet publication].
https://icd.who.int/en
[2]American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th edition (DSM-5). Washington, DC: American Psychiatric Publishing; 2022.[14]Terada S, Matsumoto Y, Sato T, et al. Factors predicting psychiatric co-morbidity in gender-dysphoric adults. Psychiatry Res. 2012 Dec 30;200(2-3):469-74.
http://www.ncbi.nlm.nih.gov/pubmed/22884214?tool=bestpractice.com
A number of external social factors including stigma, discrimination, and minority stress have been suggested as contributors.[15]Bockting WO, Miner MH, Swinburne Romine RE, et al. Stigma, mental health, and resilience in an online sample of the US transgender population. Am J Public Health. 2013 May;103(5):943-51.
https://ajph.aphapublications.org/doi/full/10.2105/AJPH.2013.301241
http://www.ncbi.nlm.nih.gov/pubmed/23488522?tool=bestpractice.com