If a father or mother from the proband is understood to hold the pathogenic variant discovered while in the proband, the risk on the sibs of inheriting the pathogenic variant is 50%. Thanks to diminished penetrance, sibs who inherit the pathogenic variant may or may not acquire aHUS (see Penetrance). https://charliewslcr.ltfblog.com/31114594/helping-the-others-realize-the-advantages-of-ahu-s