Hypothesis Paper (Part2)Abstract:The mechanisms underlying gender incongruence and/or gender dysphoria in transgender people remain insufficiently understood. This mechanistic gap has become further complicated by contemporary social discourse, and—as discussed in Part 1—greater mechanistic clarity is needed to make gender-affirming hormone therapy (GAHT) safer and more predictable. While existing literature suggests that multiple factors may contribute in combination, ethical and methodological constraints limit direct tests of the operative pathways of each factor, and broad consensus on specific mechanisms has yet to emerge. In particular, when developmental timelines are considered, sex-steroid signaling has repeatedly been discussed as a major upstream input axis, yet the timing and modes of its action remain unresolved. To interpret inter-individual variability in GAHT responses, it is also necessary to consider differences in initial conditions during developmental critical windows in which sex-steroid signaling may operate. In this context, the present paper proposes that intracellular effective exposure to testosterone may be modulated along four axes: (1) extracellular hormone availability (e.g., binding proteins such as SHBG/albumin), (2) intracellular metabolic conversion (e.g., to E2/DHT), (3) receptor/transcriptional regulatory sensitivity (e.g., AR), and (4) membrane-level input (e.g., membrane partitioning, permeability, and cellular entry dynamics). Building on this framework, we propose the “Membrane Gate Hypothesis”: during critical windows in fetal development, membrane biophysical properties may modulate membrane permeability to free testosterone, thereby altering its intracellular availability. We further summarize key determinants of membrane state and present testable predictions and falsification criteria to evaluate whether membrane biophysics can influence membrane entry and intracellular availability of free testosterone, alongside ethical guardrails to reduce risks of misuse. Disclaimer: This is not medical advice.Notes:• English is not my first language; thank you for your understanding.• For context, readers are encouraged to review Part 1 (a position paper) prior to reading this paper: https://doi.org/10.5281/zenodo.18116244
T Yoon (Tue,) studied this question.