![]() ![]() Unusually persistent, severe, or opportunistic infection is the most common presentation of SCID, particularly with viruses, fungi, or intracellular bacteria, and should prompt immunological investigation. Antibody deficiencies in particular are masked for longer by the protective effect of transplacentally acquired IgG, and present towards the end of the 1st year of life, or later. Other T cell immunodeficiencies such as major histocompatibility complex (MHC) class II deficiency and T cell activation defects often present in infancy, 10 – 12 but may present later. 9 Children presenting within the first 6 months of life are more likely to have severe combined immunodeficiency or a severe T cell defect. Persistent or recurrent oral or gastrointestinal candidiasis, or viral diarrhoea with failure to thrive are also important because, although patients with SCID are often initially well and growing normally, they fall away from the growth centile after a few months when infection occurs. Persistent respiratory infection with evidence of interstitial pneumonitis on chest radiograph should raise the suspicion of Pneumocystis carinii pneumonia, cytomegalovirus (CMV), or aspergillus infection complicating the immunodeficiency. Chest radiographs show hyperinflation, sometimes with an interstitial pneumonitis (fig 1) these children continue to exhibit symptoms, often becoming progressively worse. Infants with SCID often suffer an ongoing bronchiolitic type illness with a chronic cough and wheeze, which gradually worsens. 5 It is imperative that paediatricians recognise the clinical clues, that microbiologists alert clinicians to suggestive infections, and that immunopathologists advise promptly about the best tests and the interpretation of results. ![]() ![]() 4 Quite rightly, SCID has been described as a paediatric emergency. Infection induced end organ damage, particularly to the lungs and liver, is associated with greatly increased morbidity and mortality. Children with SCID are particularly vulnerable to community acquired infection before diagnosis. 3 Bone marrow transplantation (BMT) is curative with a very high chance of normal immunity, growth, and development, as long as the diagnosis is made early and the patient is transferred to a supraregional unit for urgent BMT. 2 Without treatment, opportunistic or otherwise self limiting infections lead to death within infancy or early childhood. 1 A variety of inherited defects prevent or severely impair T and B cell development and function. Severe combined immunodeficiencies (SCIDs) represent the most severe forms of primary immunodeficiency and have an incidence of about 1/30 000 to 1/70 000 live births. ![]()
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