Final answer:
A child without an enzyme for B and T lymphocyte development has Severe Combined Immunodeficiency (SCID). This serious inherited immunodeficiency can be fatal within the first year without a bone marrow transplant. Treatments carry risks, such as infection from donor marrow, evidenced by the 'Bubble Boy', David Vetter's case.
Step-by-step explanation:
A child born without an enzyme necessary for the development of B and T lymphocytes will have Severe Combined Immunodeficiency (SCID), a grave condition that typically leads to death within the first year due to opportunistic infections unless treated with a bone marrow transplant. This procedure can sometimes successfully correct the defects in lymphocyte development by replacing the defective components with healthy hematopoietic stem cells from a donor, as was the hope for David Vetter, also known as the 'Bubble Boy'. However, bone marrow transplants for SCID patients come with risks, as complications such as infections from latent viruses in the donated marrow can occur, which was the case with David Vetter who contracted mononucleosis leading to Burkitt lymphoma, resulting in his premature death.
SCID is considered one of the most severe of the inherited immunodeficiencies, primarily affecting both arms of the adaptive immune system - the B cells and T cells. The most common form of SCID is X-linked, affecting mainly males. With current medical advances, early diagnosis and treatment through bone marrow transplantation can offer SCID patients a chance at a prolonged life if the procedure does not result in complications from latent infections in the donor marrow.