Primary immunodeficiency diseases are usually inherited. Like anything that is inherited, these diseases are the result of altered or mutated genes that can be passed on from parent to child or can arise as genes are being copied.
One or both parents, usually healthy themselves, may carry a gene (or genes) that is somehow defective or mutated, so that it no longer produces the right protein product. If their child inherits a defective gene and does not have a normal gene to compensate, the child may show signs of immunodeficiency.
Loss of just one small molecule (if it is an important one) can impair the body’s immune system. Sometimes close relatives – brothers, sisters, cousins – also inherit the defective gene. If they do not inherit a normal gene copy they may also have immunodeficiency.
In some immunodeficiency diseases, some may have only mild symptoms, while others may have no symptoms at all.
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It is also possible to develop, or acquire, an immunodeficiency disorder during one’s lifetime. This can be the result of immune system damage due to an infection, as is the case with AIDS – the acquired immune deficiency syndrome.
An immunodeficiency can also develop as the unintended side-effect of certain drug or radiation treatments, such as those given to cancer or transplant patients.
In addition to that many environmental toxins such as polychlorinated biphenyls, iodine, lead, cadmium, smoke, cigarettes, and pesticides like DDT etc. have a suppressive effect on the immune system as do deficiencies of copper zinc vitamin E and selenium.
Malnutrition also causes secondary immune deficiency. For example protein deficiency due to malnutrition leads to reduced immunoglobulin synthesis.
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Life style and habits of an individual also interfere in immune functions. Since normal immune functions including both T and B lymphocytes activities decline with age, aging is also one of the factors for secondary immune deficiency.
As there is normal decline in immune functions, the incidence of infections, autoimmune and immune complex diseases and cancers increases with age. The progress of this acquired secondary immune deficiency disease can be reversed if the underlying cause is treatable.
Since various factors are influencing immune response secondary or acquired immunodeficiency is more common than primary immunodeficiency. The immunodeficiency disorder that tops the list in its severity of damage to the body is AIDS. It is characterized by a variety of unusual infections and otherwise rare cancers.