Managing non-SCID T cell lymphopenia after TREC-based newborn screening

Newborn screening (NBS) for severe combined immunodeficiency (SCID), based on quantifying T cell receptor excision circles (TRECs), has been increasingly implemented in screening programs worldwide. Unlike many other disorders in NBS, TREC-based screening detects many secondary findings and additional causes for T cell lymphopenia other than SCID. The clinical follow-up of SCID patients has been well implemented and documented, but newborns with other forms of T cell lymphopenia pose a new challenge for pediatric immunologists on how to offer optimal clinical management. Systematic evaluation of follow-up outcomes is crucial to establish consensus on clinical management of these patients. Here, we present clinical follow-up data of 6.5 years of NBS for SCID in the Netherlands, aiming to identify key challenges and provide recommendations. These results underscore the importance of preventing overtreatment and avoiding unnecessary prolonged follow-up and highlight the value of appropriate genetic testing and counseling. Finally, we demonstrate the critical role of international data exchange in establishing evidence-based recommendations.