A study of newborn screening for severe combined immunodeficiency (SCID) by detecting the T-cell receptor excision circle (TRECs) copy number in dried blood spots (DBSs) collected from newborns 3 days of age began in 2010 in Taiwan, and SCID screening was subsequently implemented country-wide in 2012. A total of 920,398 newborns were screened during a period of 78 months. Of these, 175 newborns (0.02%) were requested to undergo an immune function survey, and 136 cases (1 in 6768 newborns) were ultimately diagnosed as having T cell lymphopenia. The screening detected seven cases of typical SCID, with an incidence of 1 in 131,485 newborns (95% confidence interval, 1/63,693~1/271,434). Hematopoietic stem cell transplantation was performed in six patients before overt infection occurred, and the survival rate was 100%. The screening also detected eight cases of SCID variants and 20 cases of 22q11.2 deletion syndrome. Other etiologies of T lymphopenia were identified, and those newborns were evaluated and managed according to their immunological status. Owing to the introduction of newborn screening by measuring the TREC copy number, early administration of treatments became possible for newborns with conditions that put them at risk of primary or secondary immunodeficiency.
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