Androgen receptor (Androgen receptor (AR))

The androgen receptor (AR) is the cellular receptor that binds testosterone and DHT, then translocates to the nucleus to alter gene expression. The AR gene sits on the X chromosome.

Polymorphisms in the AR gene (variants in the CAG repeat length and surrounding regions) correlate with how strongly hair follicles respond to a given DHT level. People with more sensitive AR variants experience pattern hair loss earlier and to a greater extent at the same circulating androgen levels as people with less sensitive variants.

This is why family history is the strongest predictor of pattern hair loss. The folklore that “baldness comes from your mother’s side” reflects the X-linked AR component, but multiple genes contribute and both parents matter.

Anti-androgen drugs (spironolactone, cyproterone, bicalutamide) work at the AR rather than at 5α-reductase. They block the receptor instead of lowering DHT production.