First Year of TREC-Based National SCID Screening in Sweden

Area of Science:

• Immunology
• Genetics
• Pediatrics

Background:

• Severe combined immunodeficiency (SCID) screening was implemented in Sweden in August 2019.
• Newborn screening programs are crucial for early detection of primary immunodeficiencies.
• Timely diagnosis and treatment of SCID significantly improve patient outcomes.

Purpose of the Study:

• To report the initial findings from the first year of SCID screening in Sweden.
• To evaluate the performance of the newborn screening protocol for SCID.
• To estimate the incidence of SCID in the Swedish newborn population.

Main Methods:

• Quantification of T cell receptor excision circles (TRECs), kappa-deleting element excision circles (KRECs), and actin beta (ACTB) using multiplex qPCR on dried blood spots (DBS).
• Analysis of 115,786 newborns and children up to two years of age.
• Clinical assessment of 73 children referred due to low TREC levels.

Main Results:

• Three cases of SCID were diagnosed among the referred children.
• The screening demonstrated 100% sensitivity and 99.94% specificity for SCID.
• The positive predictive value (PPV) for SCID was 4.11%, and for T cell lymphopenia was 28.77%.

Conclusions:

• The Swedish newborn screening program effectively identifies SCID cases.
• The estimated incidence of SCID in Sweden is 1:38,500 newborns.
• The screening protocol shows promising performance for detecting T cell lymphopenia and SCID.