severe combined immunodeficiency disease (SCID) /sivēr″/ [L, servus, slave] , an abnormal condition characterized by the complete absence or marked deficiency of B cells and T cells, with the consequent lack of humoral and cell-mediated immunity. The disease occurs as an X-linked recessive disorder affecting only males and as an autosomal-recessive disorder affecting both males and females. It results in a pronounced susceptibility to infection and is usually fatal. The precise cause of SCID is not known, but research indicates that the disease may be caused by a cytogenic dysfunction of the embryonic stem cells that normally differentiate into B cells and T cells. The affected individual consequently has a very small thymus and little or no protection against infection. ▪ OBSERVATIONS: Pronounced susceptibility to infection usually becomes obvious 3 to 6 months after birth, when maternal immunoglobulin reserves begin to diminish. Diagnosis is difficult because B cell immunity dysfunction is hard to detect in any individual until 5 months after birth, when immunoglobulin levels should reach a low point. Infants with SCID commonly fail to thrive and have a variety of complications, such as sepsis, watery diarrhea, persistent pulmonary infections, and common viral infections that are often fatal. Some infants with SCID have mild infections and low-grade fevers that last for several months while the infant uses maternal immunoglobulin stores. These conditions generally become fatal when maternal antibodies are totally depleted. Some of the more obvious symptoms after the infant has used most of the maternal immunoglobulin stores are cyanosis, rapid respirations, and normal chest sounds with an abnormal chest radiographic picture. Maternal immunoglobulin G (IgG) is persistent, and gram-negative infections usually do not appear until after the sixth month of life. Normal infants less than 5 months of age have very small amounts of IgM and IgA, and normal IgG levels reflect only maternal IgG. The combination of several symptoms may confirm the diagnosis of SCID, including the absence or severe reduction of T cell and B cell immunity; a lymph node biopsy result that shows no lymphocytes, plasma cells, or lymphoid follicles; and no skin reaction to swabbing with dinitrochlorobenzene. Most infants with SCID die from severe infection within 1 year after birth. ▪ INTERVENTIONS: Treatment of SCID seeks to develop the immune system and to prevent infection. The only satisfactory treatment available to correct immunodeficiency is histocompatible bone marrow transplantation, but that may cause a graft-versus-host reaction, thus increasing the risk of infection and fatal consequences. Maintained enclosure in a completely sterile environment has prolonged the life of some infants with SCID, but this option is not successful if the infant has already had recurring infections. ▪ PATIENT CARE CONSIDERATIONS: Supportive treatment is the primary approach in caring for the SCID patient. The nurse tries to promote an encouraging atmosphere of growth and development while providing the parents with emotional support in the face of the nearly inevitable early death of their child. The infant must remain in strict protective isolation and benefits from diligent nursing attention, frequent parental visits, and gifts of toys, which should be the kind that can be easily sterilized.
