If a dad or mum in the proband is thought to contain the pathogenic variant discovered in the proband, the risk towards the sibs of inheriting the pathogenic variant is 50%. As a result of reduced penetrance, sibs who inherit the pathogenic variant might or might not acquire aHUS (see https://chillerhire22108.blogthisbiz.com/39601004/examine-this-report-on-air-handling-units-ahus