Screening
Infants with SCID usually appear healthy at birth. The lack of defining clinical features early in life can delay diagnosis and treatment. As a result, there has been a significant effort by some countries to develop a nationwide, population-based newborn screening (NBS) program.
Several countries (including the US, Israel, and some European countries) have initiated routine newborn screening for SCID by enumeration of T-cell receptor excision circles (TRECs) using real-time quantitative polymerase chain reaction (PCR).[26] TRECs are circular fragments of DNA that are formed in the process of generating a normal T-cell receptor and are a surrogate for the number of naive T cells that have recently emigrated from the thymus. Thus, the enumeration of TRECs by real-time quantitative PCR can be used as a screen for normal levels of naive T cells in the blood of a neonate (using dried blood spot samples). Infants with low or absent TRECs undergo lymphocyte phenotyping (total number of T cells, CD4+ T cells, CD8+ T cells, naive and memory T cells, B cells, natural killer cells) by flow cytometry and are referred for consultation with a clinical immunologist.[46] Abnormal NBS for SCID has a broad differential diagnosis, including primary and secondary causes. These include: non-SCID congenital T-cell lymphopenia (e.g., partial DiGeorge syndrome, combined immunodeficiencies), prematurity, lymphopenia secondary to cardiac and gastrointestinal diseases, and in utero exposure to immunosuppressive drugs.
SCID testing was added to the core Recommended Uniform Screening Panel from the Advisory Committee on Heritable Disorders in Newborns and Children in the US in 2010. Advisory Committee on Heritable Disorders in Newborns and Children: recommended uniform screening panel Opens in new window
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