As a protein involved in the function of the immune system, no external changes in physiology or aberrant physical characteristics are expressed by individuals possessing a<unk> . However, individuals that have a<unk>  do have a heightened susceptibility to bacterial infections, most notably caused by bacteria within the Neisseria genus, though there have also been studied cases of individuals with recurrent pneumococcus bacteremia as a result of Streptococcus pneumoniae, another species of bacteria from an entirely different phylum. Due to a heightened susceptibility to Neisseria bacterium, individuals with<unk>  are far more likely to succumb to bacterial infection such as meningitis, resulting in inflammation of the brain and spinal cord, which causes severe headaches, fevers, and neck stiffness, and may result in further development of other meningococcal diseases and extreme complications such as sepsis. Individuals with<unk>  are also more likely to catch the sexually transmitted disease, gonorrhea, as it is also caused by Neisseria bacterium, resulting in swelling, itching, pain, and formation of pus on the mucous membranes, including, but not limited to, the genitals, mouth, and rectum.
Properdin deficiency
Vitamin K deficiency
Factor I deficiency
Familial isolated vitamin E deficiency
Folate deficiency
Hypodysfibrinogenemia
Factor XIII deficiency
Factor X deficiency