Complement Protein H Deficiency is an immunological disorder caused by a deficiency of Factor H, a protein that prevents the immune system from attacking a person's own cells, but allows it to attack bacteria and viruses. It is generally caused by a genetic mutation which is most likely to express itself as the patient ages.
If the blood serum has insufficient quantity of Complement Protein H, the immune system essentially treats bacteria and viruses the same way as the patient's own cells. Patients become severely immune-impaired, and are subject to mounting numbers of bacterial infections until they succumb to toxicemia, and may also exhibit autoimmune symptoms as the body loses its ability to distinguish between harmful pathogens and normal body cells.
This disease, like most complement protein deficiencies, are extremely difficult to diagnose and are often only discovered post-mortem.