There are hardly any known deficiencies of Factor B and Factor D. However, properdin deficiency is known and is associated with mortality from Neisseria meningitides. Factor I deficiencies are rare and lead to recurrent bacterial infections. MBL deficiency increases susceptibility (Eisen 2010) to respiratory tract infections and MASP2 deficiency is associated with recurrent infections (Stengaard-Pedersen et al. 2003) and has been reported to be found in a number of different populations including Caucasians, Africans, Brazilians and Chinese (Thiel et al. 2007 ). Instances of C5, C6, C7, C8 and C9 deficiencies are known and are associated with increased susceptibility to Neisseria meningitides. However, mortality due to infection is much lower than that found with properdin deficiency.