Disease risk as a quantitative trait Susceptibility and protective genes influence the liability(risk) of developing a polygenic disease Distribution of liability in the general population Distribution of liability in the Threshold sibs of affected people +-unaffected4IH-affected Average liability Average liability High liability in general mong sibs of liability population affected peopleDisease risk as a quantitative trait: Susceptibility and protective genes influence the liability (risk) of developing a polygenic disease