Published Online: March 30, 2015
Severe Combined Immunodeficiency (SCID) is a syndrome uniformly fatal during infancy unless recognized and treated successfully by bone marrow transplantation, enzyme replacement, or gene therapy. Because SCID infants have no abnormal physical appearance, diagnosis is usually delayed unless newborn screening is performed. Newborn screening is now available in several states but is not yet universal, requiring providers to recognize the constellation of symptoms and laboratory values suggestive of SCID to make the diagnosis.
An article by McWilliams et al, recently published in The Journal of Allergy and Clinical Immunology: In Practice, describe the presenting features of a cohort of 172 SCID patients receiving bone marrow transplantation by Dr. Rebecca Buckley and team at Duke University Medical Center. The mean age at presentation was 4.87 months. When there was a family history of early infant death or known SCID, the mean presentation age was much earlier, 2.0 months compared to 6.6 months. Failure to thrive was common, with 84 patients (50%) having a weight less than the 5th percentile. The leading infections included oral moniliasis (43%), viral infections (35.5%), and Pneumocystis jiroveci (26%) pneumonia. Eighty eight percent of the infants had an Absolute Lymphocyte Count (ALC) less than 3000/cmm. Absent thymic shadow was seen in 92% of infants with electronic radiographic data available. An absence of T cell function was found in all patients.
SCID infants appear normal at birth but later present with failure to thrive and/or recurrent fungal, viral, and bacterial infections. Low ALCs and absent thymic shadow on chest x-ray are key diagnostic clues. The absence of T cell function confirms the diagnosis.
This study may lead to increased recognition of SCID until newborn screening is implemented in all states and before live vaccines are administered.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.