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Primary immunodeficiency diseases (PIDs) encompass a spectrum of conditions that result from more than 300 congenital defects of the immune system. These intrinsic molecular changes alter the development or function of the immune system, leading to increased susceptibility to infections, neoplasia, autoinflammation, and autoimmunity. PIDs occur more commonly than often perceived, existing at an estimated prevalence of 1 in every 1200 individuals in the United States. Higher incidence and prevalence can be expected in parts of the world with genetically homogenous populations or consanguinity. The different PIDs are established by the International Union of Immunological Societies (IUIS) and comprise 8 categories, plus an additional category for PID phenocopies, covering essentially all aspects of immune cell biology and immune function. This chapter will review distinguishing features of 7 of the 8 categories, leaving complement deficiencies for discussion in a separate chapter.
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COMBINED CELLULAR AND HUMORAL IMMUNODEFICIENCIES
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Combined cellular and humoral immunodeficiencies are characterized primarily by decreased function of T cells, B cells, and sometimes natural killer (NK) cells (Table 184-1). In many cases, the T cell deficiency leads or contributes to loss of B-cell function. Within this classification scheme, severe combined immunodeficiency disease (SCID) carries distinction from other combined immunodeficiencies (CIDs).
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SEVERE COMBINED IMMUNODEFICIENCY DISEASE
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Children with SCID are born with marked susceptibility to ...