Here it is - formatting's a bit fucked:
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A few weeks back, I stumbled on the Steph's Place website, where in the "Truth and Lies" section, it offered the explanation:IS THERE A MEDICAL EXPLANATION FOR BEING TRANS:? In regards totrans women, this is because the template (default) for a human being in the womb is female. Males are made out of females. Sometimes nature makes "mistakes", and some people get female brains but with male genitals."I am a biologist, andI mainly studymolecular and cell biology in the context of cancer research, but like all sciences, my work is highly interdisciplinary and intersectional.My current research is in neuroscience, though not directly related to the topic of transgender study.It is a topic of great interest to me, however, and Ihavebeen following itover the past year.With that, I wanted to offer some information to qualify this statement.In this letter:“Gender” refers to own-body perceptionof male, female, or non-binaryregardless of social presentation. The two are usually intertwined, but as we know, many trans people do not socially or physically transition due to safety concerns, social pressure, or lack of distress.“Sex” refers to appearance of genitalia at birth,in accordance with the medical definition most applicable to humans. The only people who care about your gametes are fertility doctors,sperm banks,potentialparental partners, and creeps.Sex chromosomes are not socially relevant. The majority of us don’t even know our karyotype (complete set of chromosomes), and we get along just fine without that information.While the explanation on the webpageis correct in thatwhat we consider“female”isthe default and males are differentiated by expression of the SRY gene(usually, but not always on the Y chromosome), the brain begins developing3-5 weeks into gestation, and the genitals begin differentiation about 8-9 weeks in. They develop independently, which gives rise to the hypothesis that hormones in uteroinfluence the development of gender.Currently, we know of no biological mechanism to keep the two congruent, so abetter question is really, “whatcouldpreventthem from varying?”Hence, the explanation on the Steph's Place website was a bit misleading -though I'm sure it's intentionally brief because the subject matter is highly complex.There is a neurobiological explanation for being transgender.Relatively recently, neurologists have been able to measure connectivityin the medial prefrontal cortex, aregion whichgovernsour self-perception and self-reference, using a method called fractional anisotropy (FA)”. FA is used to measureconnectivity in the tracts of white matter in the brain.
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So far, I know of two studies by different research teams whohave isolated sexually (or "genderly", in this case) dimorphic connectivityin the fronto-occipitofasciculus (or "inferior frontal-occipital fasciculus", IFOF)using FA. The IFOF is thetract of white matter which connectsthe frontal lobe to the occipital and parietal lobes and the postero-temporal cortex–so dealing with sensory(visual, spatial, touch, etc)and language processing.The prefrontal cortex is the front of the frontal lobe, and the medial prefrontal cortex, as implied by the name, isin the middlefrom top-to-bottom.The parietal lobe is another region whichgoverns own-body perception.These FA studies have found that, in the IFOF specifically,trans women have morefemale-typical patterns of connectivity, and trans men havemore male-typical patterns–though on average, both seem to be more intermediary rather than fully masculinised or feminised (i.e. some people are more in-between than others).1,2Connectivitywhich is closer to “down the middle”is likely where non-binary identities and gender fluidity arise, but more research is needed.Thisinformationis consistent with what we know about the cognitive differences between men and women: men tend to perform better at spatial tasks (parietal lobe), and women perform better on verbal tasks (frontal lobe). Trans men and trans women follow these trendsfor such tasks, with trans men showing male-typical performanceand trans women showing female-typical performance.More studies have found differences in sizes of brain structures and cortical thickness in transgender people that correspond to their gender. 3,4,5REVIEW,6,7,8,9Thus, a female pattern of connectivity is incongruent with a male phenotype (physical appearance) and vice-versa, giving rise to the gender incongruence experienced bytransgender people. Gender incongruenceitselfis not pathological –that is why being transgender is no longer classified as a mental illness by any accredited psychiatric or medical association. Current data supports that being transgender issimply neurobiological variation.Gender dysphoria (GD), however, can become a mental illness (disorder) if it causes significant changes in mental functioning and/or distress in a person’s daily life, and soitis deserving of treatment and/or prevention. A possible explanation for GDisthat sex-incongruentpatterns of connectivityareincompatible with the size and shape of brain structuresthat come from hormone exposure in the uterus after sex differentiationbegins.This is consistent with findings that gender dysphoria frequently worsensat the onset of puberty, when sex hormones begin to be produced and effectchangesin the brain.Itis also consistent with the observation that nearly all people with complete androgen insensitivity syndrome (cAIS) live and identify as women, with one known exception. cAIS renders a personincapable of being androgenised (“complete” is literal–no cellsin their bodies can respond to testosterone)due to a mutation ofthe androgen receptor.cAIS affects roughly 1 in 20,000 people(any karyotype)and roughly 0.05% of the population is transgender, so we would expect at least 1,000people with cAIS to be transgender, which we do not.
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To summarise: the genitalsand the brain develop independently, and we know of no biological process which forcesthem to align. Therefore, we have no reason to believe theemergence of transgender individuals in any population is in any way preventable.Trans people exist because they have brain connectivity patterns of one gender andthesexual characteristics of the opposite sex.Trans people oftenrequiregender-affirmingtreatment to resolve or prevent gender dysphoriaas itcan cause severe harmto their mental health and ability to function in society–this is at the discretion of themselves and their medical and mental health providers. In youth, consent of their guardians and usually multiple psychiatric referrals are required.Trans people and their healthcare providers are the two “sides” to this “debate”, and the debate topic is their healthcare needs and well-being.Gender is adistinct characteristic from sex.It is not voluntarily mutable, but in rarecases, individuals have reported their gender identityhadchanged over time–much like how sexual orientation may change for some people. To my knowledge, neurological studies for such cases arenot yetavailable but maysomedaybe –it could be rather difficult because these cases are so rarely reported.Yourreaders may be able to access the full text of some of these studies, so I am providing links to myreferences in case they would like to explore them. Manyare neurosciencepapers, so some can be difficult to follow if you don't have a background or at least a keen interest.
1.www.nature.com/articles/s41598-017-17352-8
2.www.cambridge.org/core/journals/psychological-medicine/article/alterations-in-the-inferior-frontooccipital-fasciculus-a-specific-neural-correlate-of-gender-incongruence/FF4254F98E6387488D2AA2BD30D7D3A7
3.journals.plos.org/plosone/article?id=10.1371/journal.pone.0083947
4.www.sciencedirect.com/science/article/pii/S030645309800033X
5.neurosciencenews.com/gender-dysphoria-brain-15275/
6.academic.oup.com/cercor/article/27/2/998/3056235
7.link.springer.com/article/10.1007/s11682-016-9578-6
8.link.springer.com/article/10.1007/s10508-015-0596-z
9.www.sciencedirect.com/science/article/pii/S1477513110002020
10.www.ncbi.nlm.nih.gov/pmc/articles/PMC7197078/
11.link.springer.com/referenceworkentry/10.1007/978-0-387-79948-3_32
12.pubmed.ncbi.nlm.nih.gov/17536964/
13.www.ncbi.nlm.nih.gov/pmc/articles/PMC5354991/
14.pubmed.ncbi.nlm.nih.gov/35940875/
15.www.ncbi.nlm.nih.gov/pmc/articles/PMC6234077/
The first-linked study is full of references to other neurological studies on the 'trans brain'. Somereport finding no differences inother regions of thebrains of transand cispeople using other techniques and FA-that's why the first-linked studyset out toisolate the exact region where differences are seen(the IFOF). Overall findings are,however, consistent.
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It is worth noting that FA, to my knowledge, is not currently used as a diagnostic marker, andwhen it is, its utility is in neurodegenerative disorders. It isunlikely to become a “test” to identifytransgender individuals; that role is already filled bypsychologists and medical practitioners, whose support will remainnecessary regardless of any possible testing.It is unlikely to work in foetuses because they move, which muddles theresults.Ethical implications aside: currently, there is no data on when own-body perception in the context of gender finishes developing–for all we know, it continues to do soafter birth.Gender incongruence not being pathological, there is noreason to “test” for itany more than there is for being left-handed,other thanforpersonal curiosity.There is still much to discoveron this topic, soI look forward to readingmore studieswhich expoundon these findingsin the coming years.I just thought I’d share what we have for nowas I rarely see it discussed, and that’s a shame because I find it rather interesting.
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