Review of a Decade of International Experiences in Severe Combined Immunodeficiency Newborn Screening Using T-cell Receptor Excision Circle

Severe Combined Immunodeficiency Disorders (SCIDs) are a diverse group of monogenic inborn errors of immunity (IEIs) characterised by severe lack of T lymphocyte number and function, with or without affecting B and NK lymphocyte numbers. Severe infections lead to early infant death. SCID infants are seemingly well prior to onset of infections, causing them to miss the golden window for haematopoietic stem cell transplant (HSCT) prior to the age of newborn screening. T cell receptor excision circle is a clinical marker for naive T cell number and can be used to screen for SCID with high sensitivity. International experiences showed that no classical SCIDs have been missed by screening programs so far. Due to extremely favourable outcomes (90% long term survival) for SCID patients picked up by screening and savings incurred by early HSCT, screening for SCID with TREC assay is great value for money. Hong Kong should join the global trend of screening for SCID and save the lives of SCID children.