Again, what is transgenderism ... ?

The Diagnostic and Statistical Manual 5 (DSM-5) is the reference created and used by psychiatrists for defining the diagnostic criteria of various mental health disorders.  As might be expected, there is considerable overlap of symptoms and behaviours among various disorders, and much subjectivity in drawing distinctions, and we still have a through-a-keyhole understanding of mental health, all combining to limit the DSM-5 in its attempt to be authoritative.

In its discussion of gender dysphoria disorder, it falls into the trap of conflating gender and sex:

"Thus, gender is used to denote the public (and usually legally recognized) lived role as boy or girl, man or woman, but, in contrast to certain social constructionist theories, biological factors are seen as contributing, in interaction with social and psychological factors, to gender development. Gender assignment refers to the initial assignment as male or female. This occurs usually at birth and, thereby, yields the “natal gender.” Gender-atypical refers to somatic features or behaviors that are not typical (in a statistical sense) of individuals with the same assigned gender in a given society and historical era; for behavior, gender-nonconforming is an alternative descriptive term. Gender reassignment denotes an official (and usually legal) change of gender. Gender identity is a category of social identity and refers to an individual’s identification as male, female, or, occasionally, some category other than male or female. Gender dysphoria as a general descriptive term refers to an individual’s affective/cognitive discontent with the assigned gender but is more specifically defined when used as a diagnostic category. Transgender refers to the broad spectrum of individuals who transiently or persistently identify with a gender different from their natal gender."

"Natal gender," for the majority of us who are born without biologic sex ambiguity, is biologic sex.  For those of us with unambiguous biologic sex, our sex is not "assigned", it simply is.

Here is the DSM-5 definition of delusions:

"Delusions are fixed beliefs that are not amenable to change in light of conflicting evidence. Their content may include a variety of themes (e.g., persecutory, referential, somatic, religious, grandiose)."

While it seems obvious that transgenderism is a delusion, the definition goes on to state:

"Delusions are deemed bizarre if they are clearly implausible and not understandable to same-culture peers and do not derive from ordinary life experiences."

thus laying the solipsistic groundwork that if enough people agree with the delusion, it is no longer a delusion.

And then there is somatic disorder, which is meant to capture people who are preoccupied with various physical sensations, but when read through the lens of transgenderism, opens another etiologic view:

"Diagnostic Criteria

300.82 (F45.1)

1. One or more somatic symptoms that are distressing or result in significant disruption of daily life.
2. Excessive thoughts, feelings, or behaviors related to the somatic symptoms or associated health concerns as manifested by at least one of the following:
   1. Disproportionate and persistent thoughts about the seriousness of one’s symptoms.
   2. Persistently high level of anxiety about health or symptoms.
   3. Excessive time and energy devoted to these symptoms or health concerns.
3. Although any one somatic symptom may not be continuously present, the state of being symptomatic is persistent (typically more than 6 months)."

"The major diagnosis in this diagnostic class, somatic symptom disorder, emphasizes diagnosis made on the basis of positive symptoms and signs (distressing somatic symptoms plus abnormal thoughts, feelings, and behaviors in response to these symptoms) rather than the absence of a medical explanation for somatic symptoms. A distinctive characteristic of many individuals with somatic symptom disorder is not the somatic symptoms per se, but instead the way they present and interpret them. Incorporating affective, cognitive, and behavioral components into the criteria for somatic symptom disorder provides a more comprehensive and accurate reflection of the true clinical picture than can be achieved by assessing the somatic complaints alone."

"A number of factors may contribute to somatic symptom and related disorders. These include genetic and biological vulnerability (e.g., increased sensitivity to pain), early traumatic experiences (e.g., violence, abuse, deprivation), and learning (e.g., attention obtained from illness, lack of reinforcement of nonsomatic expressions of distress), as well as cultural/social norms that devalue and stigmatize psychological suffering as compared with physical suffering. Differences in medical care across cultures affect the presentation, recognition, and management of these somatic presentations. Variations in symptom presentation are likely the result of the interaction of multiple factors within cultural contexts that affect how individuals identify and classify bodily sensations, perceive illness, and seek medical attention for them. Thus, somatic presentations can be viewed as expressions of personal suffering inserted in a cultural and social context."

"All of these disorders are characterized by the prominent focus on somatic concerns and their initial presentation mainly in medical rather than mental health care settings."

"Somatic symptoms are prominent in various “culture-bound syndromes.” High numbers of somatic symptoms are found in population-based and primary care studies around the world, with a similar pattern of the most commonly reported somatic symptoms, impairment, and treatment seeking."

"It is important to note that some other mental disorders may initially manifest with primarily somatic symptoms (e.g., major depressive disorder, panic disorder). Such diagnoses may account for the somatic symptoms, or they may occur alongside one of the somatic symptom and related disorders in this chapter. There is also considerable medical comorbidity among somatizing individuals. Although somatic symptoms are frequently associated with psychological distress and psychopathology, some somatic symptom and related disorders can arise spontaneously, and their causes can remain obscure. Anxiety disorders and depressive disorders may accompany somatic symptom and related disorders. The somatic component adds severity and complexity to depressive and anxiety disorders and results in higher severity, functional impairment, and even refractoriness to traditional treatments. In rare instances, the degree of preoccupation may be so severe as to warrant consideration of a delusional disorder diagnosis."

(Italics mine.  I couldn't help but highlight that whole last paragraph!)

And what underlies delusional disorders, somatic disorders, and transgenderism?  Anxiety.  What is anxiety?

"Anxiety disorders include disorders that share features of excessive fear and anxiety and related behavioral disturbances. Fear is the emotional response to real or perceived imminent threat, whereas anxiety is anticipation of future threat. Obviously, these two states overlap, but they also differ, with fear more often associated with surges of autonomic arousal necessary for fight or flight, thoughts of immediate danger, and escape behaviors, and anxiety more often associated with muscle tension and vigilance in preparation for future danger and cautious or avoidant behaviors."

What is the basis of excessive fear in transgenderism?  Feeling trapped in entrenched and enforced gender roles in the oppressive culture of patriarchy.