Involves deficient or absent cell-mediated (T cell) and humoral (B cell) immunity

Predisposes patient to infection from all classes of microorganisms during infancy

Occurs in 1 of every 100,000 to 500,000 births, affecting more males than females, but is difficult to detect before an infant reaches age 5 months

Also known as SCID, graft-versus-host disease, and bubble-boy disease

Three types of SCID have been identified:

Failure of thymus or bursa equivalent to develop normally or possible defect in thymus and bone marrow (responsible for T- and B-cell development)

Possible enzyme deficiency

Transmitted as autosomal recessive trait but may be X-linked

Extreme susceptibility to infection within the first few months after birth, but probably no sign of gram-negative infection until about age 6 months because of protection by maternal immunoglobulin G