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Primary immunodeficiency diseases are genetic disorders that affect the immune system, causing recurring infections. Symptoms vary depending on which part of the immune system is affected. Treatment varies depending on the type of disorder, with stem cell transplants being reserved for severe cases.
Primary immunodeficiency diseases are those in which 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 the disease. This means, for example, that the immune dysfunction cannot have been caused by medications or other ailments. Consequently, most primary immune diseases are genetic disorders diagnosed in very young children.
In most types of primary immunodeficiency disorder, the core symptoms are a result of the immune dysfunction itself. However, there are different types of primary immune disorders and symptoms can vary slightly. Primary immune disorders differ in terms of which part of the immune system is dysfunctional and this affects the type of symptoms that appear.
About half of primary immunodeficiency disorders are caused by a lack of functional antibodies. One example is X-linked agammaglobulinemia, also known as XLA. This X-linked recessive disease affects boys, while women with the defective gene are carriers. Babies born with XLA are protected for the first few months of life by antibodies supplied by the mother in utero and in breast milk. Once this protection dissipates, they begin to suffer from recurring bacterial infections and are also at risk for 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 experience recurring infections of a very specific type. In particular, they are vulnerable to pneumonia, skin abscesses and skin infections, and blood and bone marrow infections.
Another type of primary immunodeficiency affects the complement cascade, a molecular chain reaction that is triggered by bacterial infection and leads to the formation of complement proteins. These molecules, along with antibodies, help kill invading bacteria. The complement cascade itself is a relatively minor part of the immune system, and as a result, many people are not diagnosed with complement deficiency until they reach adulthood. People with this type of immunodeficiency retain fully functional T and B cells and are protected from most infections. In some cases, they can be vulnerable to certain types of diseases, including blood-borne infections.
There are eight different classes of primary immune disorders and more than 120 different conditions that fall into one of these categories. Each class of disorder tends to require different treatment, due to the involvement of different 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 require no treatment.
Very serious 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 this way, including XLA, but stem cell treatment is not often done on people with XLA unless other treatment options fail.
