Primary immunodeficiency diseases are those in which some part of the immune system is dysfunctional or absent altogether. For an immune disorder to be considered primary, the immune dysfunction itself must be the underlying cause of disease. This means, for example, that the immune dysfunction cannot have been caused by medications or other disorders. Consequently, the majority of primary immune disorders are genetic disorders that are diagnosed in very young children.
In most types of primary immunodeficiency disorder, the main symptoms are a result of the immune dysfunction itself. There are several types of primary immune disorder, however, and symptoms can vary somewhat. Primary immune disorders differ in terms of the part of the immune system which is dysfunctional, and this affects which kind of symptoms appear.
Around half of primary immunodeficiency disorders are caused by lack of functional antibodies. One example is x-linked agammaglobulinemia, also known as XLA. This x-linked recessive disorder affects male children, while women with the defective gene are carriers. Children born with XLA are protected for the first few months of life by antibodies provided by their mother in utero and in breast milk. Once this protection dissipates they begin suffering from recurrent bacterial infections, and are also at risk of secondary complications such as meningitis.
In contrast, chronic granulomatous disease is a type of primary immunodeficiency disease caused by the inability of phagocytes to kill organisms once they have been ingested. Children with this disorder suffer from recurrent infections of very specific types. In particular, they are vulnerable to pneumonia, skin abscesses and skin infections, and infections of the bone marrow and blood.
Another type of primary immunodeficiency affects the complement cascade, a molecular chain reaction which is triggered by bacterial infection and results in the formation of complement proteins. These molecules, in conjunction with antibodies, help kill invading bacteria. The complement cascade itself is a relatively minor part of the immune system, and as a consequence many people are not diagnosed with complement deficiencies until after they reach adulthood. People with this type of immunodeficiency retain fully functional T cells and B cells, and are protected from most infections. In some cases, they may be vulnerable to certain types of diseases, including bloodborne infections.
There are eight different classes of primary immune disorder, and more than 120 different conditions which fall into one of these categories. Each class of disorder tends to require different treatment, due to the involvement of diverse parts of the immune system. XLA, for example, is successfully treated with regular doses of protective antibodies to boost passive immunity to infection. Chronic granulomatous disease is often treated with prophylactic antibiotics, while some types of complement deficiency do not require any treatment.
Very severe immune disorders can be treated with stem cell transplants. This treatment is normally reserved for diseases such as severe combined immunodeficiency. People with this disorder have no functional T cells or B cells, and are vulnerable to virtually all types of infection. Other types of primary immunodeficiency can be treated in this way, including XLA, but stem cell treatment is not often carried out on people with XLA unless other treatment options fail.