Most infants are exposed to pathogens during this period, but have some ability to fight infections as their immune system develops. Following birth, newborns have high levels of maternal antibodies to provide protection from pathogens until the newborn’s immune system develops over the next few months. Genetic mutations in SCID disorders preclude normal production and maturation of T-cell lymphocytes and/or B-cell lymphocyte secretion of antibodies, thus preventing development of a normal, healthy immune system. Genetic counseling services for families of infants with SCID are highly recommended. Several autosomal recessive genetic mutations also may cause SCID. Females are not affected, although they have a 50 percent chance of being carriers of the gene mutation and may pass this mutation to any future offspring.

In XSCID, males inherit the X-linked gene mutation from carrier mothers. While all forms of SCID are due to specific gene mutations, some individuals affected with the disorder have the X chromosome linked form, XSCID. The incidence for all types of immunodeficiency may be closer to one in every 15,000 births. The incidence of SCID is estimated at one in every 50,000 births.

Rotavirus vaccine is contraindicated for infants with defects in T lymphocyte production and function, and severe, prolonged episodes of gastroenteritis have been reported in infants with SCID following administration of this vaccine. Live, attenuated vaccines should not be administered to infants diagnosed with, or suspect for SCID. Infants who receive a transplant within the first few months of life, especially before onset of more serious infections or complications, have a greatly improved survival rate. The treatment for SCID is hematopoietic stem cell/bone marrow transplant. Although newborn screening is intended to identify newborns with SCID, additional types of lymphopenia and other disorders including complete DiGeorge syndrome or congenital intestinal lymphangiectasia also may result in positive newborn screens due to the absence of lymphocytes. In some cases, if the newborn screening is inconclusive or the blood sample is inadequate for DNA testing, a second newborn screening sample may be requested for testing. If newborn screening results indicate low levels of TRECS, referral should be made to a pediatric immunologist designated by the Department for diagnostic flow cytometry. The absence of TRECS or lower numbers of TRECS may indicate the newborn has SCID or profound T-cell lymphopenia. TRECS are formed during normal immune system development as T-cell lymphocytes within the thymus gland undergo differentiation and specialization following exposure to antigens. In Illinois, newborn screening for SCID is performed by measuring the T-cell receptor excision circles (TRECS) in DNA extracted from dried blood spot samples. Newborn Screening and Definitive Diagnosis

Infants with SCID also may suffer from poor nutrition and “failure to thrive.” Without early diagnosis and treatment, children with SCID usually succumb to infectious disease complications during the first or second year of life. Often these infections are prolonged and do not respond to usual therapies, and some may require intravenous antibiotics. Early symptoms may include frequent bouts of ear infections, thrush, bronchitis, pneumonia and diarrhea. Lacking adequate immune system defenses, these infants are very susceptible to multiple life threatening infections. Newborns with SCID usually appear healthy at birth and may have no family history of immunodeficiencies. All forms of SCID are inherited and not acquired as side-effects of infection or immune response suppression therapies. Individuals with SCID are very susceptible to recurrent infections and without treatment may succumb to pneumonia, meningitis or other infection related complications. These lymphocytes serve as primary defenses in the identification of invading viruses, bacteria and fungi and help facilitate the immune system’s response to pathogenic invasion. Severe combined immune deficiency (SCID) includes a group of rare inherited disorders in which genetic defects cause improper development of special white blood cells, the T lymphocytes. Severe Combined Immune Deficiency Information for Physicians and Other Health Care Professionals Definition

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