If a dad or mum from the proband is understood to have the pathogenic variant determined within the proband, the danger into the sibs of inheriting the pathogenic variant is 50%. As a consequence of decreased penetrance, sibs who inherit the pathogenic variant may or may not acquire aHUS (see https://ahu-hire20863.glifeblog.com/31119480/the-fact-about-air-handling-units-ahus-that-no-one-is-suggesting