In November 2023, the Children and Families Agency announced the implementation of newborn screening (NBS) for severe combined immunodeficiency (SCID), which has since been expanded nationwide in Japan. In Saitama Prefecture, expanded NBS using T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC) was initiated in September 2024. We report the first-year outcomes of expanded NBS for primary immunodeficiency (PID) in Saitama Prefecture.
Expanded NBS was initiated in Saitama Prefecture (excluding Saitama City) in September 2024 and in Saitama City in April 2025. A regional consortium was established to coordinate sample collection, laboratory testing, and confirmatory evaluation. PID screening was performed using the NeoMDx kit (Revvity). Cutoff values for positive screening were defined as TREC <300 copies/105 cells and KREC <250 copies/105 cells.
Between September 1, 2024, and August 31, 2025, a total of 35,248 newborns were screened. The recall rate for retesting was 58 cases (0.16%), repeat sampling was required in 42 cases (0.12%), and 12 cases (0.03%) required further diagnostic evaluation. Among these, two PID cases were identified and successfully treated: one case of complete DiGeorge syndrome/CHARGE syndrome and one case of X-linked agammaglobulinemia. Additional diagnoses included three infants born to mothers receiving immunosuppressive therapy, one infant born to a mother treated with biologic agents, one case of Langerhans cell histiocytosis, one case of trisomy 21 with transient abnormal myelopoiesis, one case of fetal hydrops/cardiofaciocutaneous (CFC) syndrome, one case of neonatal asphyxia with steroid exposure, and two cases of B cell lymphopenia.
Expanded NBS enabled not only the life-saving identification of two patients with PID but also appropriate clinical management of infants with positive screening results. Continued efforts to improve public awareness, quality control, and regional collaboration are essential to further optimize early diagnosis and treatment.
