An immune deficiency disease may be caused either by an inherited defect in the cells of the immune system or by an environmental agent. In the case of an inherited defect, the resulting disease is referred to as primary immune deficiency disease. According to the World Health Organization, there are more than 200 of these sometimes life-altering or life-threatening inherited defects – some are relatively rare, some are quite common. Primary immune deficiency disease affect many thousands of children and adults in the U.S.
When the damage is caused by an environmental agent, the resulting disease is referred to as secondary immune deficiency disease. Secondary immune deficiencies can be caused by exposure to radiation or toxic chemicals, chemotherapy, malnutrition and burns.
Immune deficiency is a state in which the immune system’s ability to fight infection is compromised or entirely absent. The most apparent sign of an immune deficiency is frequent illness. Because a normal immune system protects the body against infection, patients with primary immune deficiencies are more susceptible to infections of all kinds. Those infections commonly involve skin, sinuses, throat, ears, lungs, brain, spinal cord, urinary tract and intestinal tract. The increased vulnerability to infection may result in repeated infections, infections that won’t clear up or unusually severe infections. People with primary immune deficiencies often develop serious and debilitating illnesses. Fortunately, with proper medical care, many patients live full and independent lives.
A number of the more rare primary immune deficiencies are diagnosed in early childhood and result in shortened lives with extreme susceptibility to infection and malignancy. Primary among those are CVID (Common Variable Immune Deficiency) and SCID (Sever Combined Immunodeficiency):
Common Variable Immune Deficiency (CVID) is generally diagnosed between age 2 and young adulthood and is characterized by increased susceptibility to infection and diminished response to vaccines. Individuals with CVID may develop meningitis or other systemic bacterial infections, recurrent eye or skin infections and gastrointestinal symptoms that include chronic diarrhea and bloating. They also have increased susceptibility to malignancies, especially lymphomas, and may develop breast cancer, prostate cancer and skin cancer.
Severe Combined Immunodeficiency (SCID) represents a group of rare, sometimes fatal, primary immune deficiencies characterized by one or more serious, life-threatening infections within the first few months of life. They may include pneumonia, meningitis or bloodstream infections. SCID is the result of an immune system so highly compromised that it is considered almost absent.
Chronic diarrhea, recurrent pneumonia, ear infections and profuse oral candidiasis (thrush) are commonplace. SCID, or “bubble boy disease,” became a household name during the 1970’s with the filming of David Vetter, a boy who lived for 12 years in a plastic, germ-free bubble. The defining feature of SCID is a defect in the specialized white blood cells (B- and T-lymphocytes) that defend us from infection by viruses, bacteria and fungi. Without a functional immune system, SCID patients are susceptible to recurrent infections and may die before the first year of life. Bone marrow and stem cell transplants save as many as 80% of SCID patients.
The most commonly quoted figure for the prevalence of primary SCID is around 1 in 100,000 births, although this is regarded by some as an underestimate of the true prevalence. A figure of about 1 in 65,000 live births has been reported for Australia.
Recent studies indicate that one in every 2,500 children in the Navajo population inherit SCID, a significant cause of illness and death among Navajo children. Ongoing research reveals a similar genetic pattern among the related Apache people.
All forms of primary SCID are inherited, with as many as half of SCID cases linked to the X chromosome, passed on by the mother. A mutation in JAK3, located on chromosome 19, can also result in SCID.
SCID may also be known as Alymphocytosis, Glanzmann–Riniker Syndrome, Severe Mixed Immunodeficiency Syndrome and Thymic Alymphoplasia.