A newly found homozygous mutation in recombination activating gene 1 in a patient with leaky severe combined immunodeficiency disorder.

The recombination activating genes, including RAG1 and RAG2, are essential for V(D)J somatic recombination in lymphocytes. Leaky severe combined immunodeficiency disorder (SCID) is characterized by normal or intermediate T cells and normal to absent B cells associated with partial T cell and B cell dysfunction. We present a newly found RAG1 deficiency in a 21-year-old boy with leaky SCID. Immunoglobulin levels, flow cytometry, and whole exome sequencing (WES) were evaluated. Flow cytometric analysis revealed a decreased number of CD3+, CD4+, and CD8+ T cells, and B cells whereas NK cell counts were normal. Immunoglobulin levels were also decreased. The WES revealed a newly found homozygous mutation of RAG1 gene (NM_000448: exon 2: c.C2275T). Atypical features, including leukopenia, candidiasis, and low lymphocyte counts in patients with late-onset combined immunodeficiency disorders (CID) such as leaky SCID due to RAG1 deficiency may result in misdiagnosis and inadequate therapy instead of adopting the curative hematopoietic stem cell transplantation in these patients.