I literary wrote about this three posts above as I have written about this many times elsewhere but apparently I am not getting this simple point across.
Serum DHT in normal ranges does not mean that DHT concentrations in key tissues responsible for sexual function are in normal ranges.
There is little correlation between serum and tissue concentrations of DHT (reference provided elsewhere), especially because tissue concentrations of DHT in key organs such as the prostate are (or need to be) ten times higher than in serum.
Further, serum DHT can be supplied by other tissues that are not deficient in 5a-reductase, such as the tissues that express 5ar-type 1.