Thread by @FondOfBeetles

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport Here's the anatomical description:
People with 5ARD have XY chromosomes and develop testes in utero. Their testes make normal amounts of testosterone (T), and their response to testosterone (via the androgen receptor; AR) is not compromised.

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport In response to T, male internal genitalia (the ductal system that moves sperm from testes to penis) develops normally. Their testes also make normal amounts of anti-Mullerian hormone (AMH), acting to repress development of female internal genitalia (uterus and so on).

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport The next developmental step in males - shaping the scrotum, penis and prostate - is the hierarchy of sex development at which 5ARD manifests. Male external genitalia development is triggered not by T but a derivative of T called dihydrotestosterone (DHT).

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport In males, T is converted to DHT by the 5-alpha reductase enzyme. Males with 5ARD are unable to convert sufficient T to DHT to drive male-typical external genitalia. Consequently, external genitalia can develop as female-typical, and may be observed as such at birth.

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport At puberty, T production surges to drive male-typical sexual maturity - phallic growth, muscle mass, voice change - although extent of virilisation varies. 50% of those assigned female adopt a male identity. Sperm production and fertility is possible. End/

@berthadalziel @SwipeWright @MianneBagger @Scienceofsport And on sporting performance:
The IAAF argued that, in terms of sporting performance, 5ARD women are equivalent to healthy male athletes, thus 5ARD women should not be permitted to compete in the female category unrestricted.