In Brynhildr in the Darkness, all of the magicians seem to be female - but there doesn't seem to be a reason for this (in the manga at least).
If we look at Okamoto Lynn's other work, Elfen Lied, he explains that male Diclonius are possible, but lack the vectors that the females have due to inbreeding. This explains why they are not that commonly seen in the series. I haven't been able to find a similar reason for Brynhildr though.
Is there any similar reasoning for why all the magicians are female in Brynhildr?