If a dad or mum on the proband is understood to possess the pathogenic variant discovered within the proband, the risk on the sibs of inheriting the pathogenic variant is 50%. As a result of minimized penetrance, sibs who inherit the pathogenic variant may or may not create aHUS (see https://ahu-hire49370.livebloggs.com/38257121/a-secret-weapon-for-ahu-hire