Immunodeficiency
Immunodeficiency means that the immune system does not function properly, and the child is therefore subject to repeated episodes of infection. The defect can be inherited, or secondary to another disease process such as vitamin deficiency in malnutrition, treatment with immunosuppressant agents post organ transplant, Cancer - or its treatment - affecting the bone marrow, removal of the spleen or HIV infection (described in this section).
Inherited deficiencies may be X-linked - which means the mother carries the defective gene responsible for the disease on one of her X chromosomes, and if this is the one she transmits to her son then he develops the disease - such as Agammaglobulinaemia, where there is failure of production of gammaglobulins as a result of B-cell abnormalities - the treatment of which requires gammaglobulin replacement. Rather than affecting lymphocytes, some inherited deficiencies affect the white cells that attack bacteria - the neutrophils. In Chronic Granulomatous Disease, which is inherited both as an X-linked disorder and in a less severe form as an autosomal recessive disease (which means both chromosomes must be abnormal for you to develop the disease, that you've inherited one from each parent, and that girls can develop it too); while the cells can attack the bacteria they fail to kill them, because one of their enzyme systems does not function. There are a number of other, rarer, inherited deficiencies affecting either T-cells, B-cells or both.
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