Lessons learned from the diagnostic work-up of a patient with the bare lymphocyte syndrome type II

A patient presented severe combined immunodeficiency (SCID)-like symptoms. The presence of a substantial number of CD4⁺ T-cells in the peripheral blood was not explained by maternal engraftment. Genetic analysis revealed a novel RFXANK mutation, c.232C > T, resulting in a stop codon, with consequently defective transcription of MHC class II resulting in bare lymphocyte syndrome (BLS) type II. The initial unawareness of complete absence of MHC class II expression and normal T-cell receptor excision circles (TREC)-levels delayed the final diagnosis. After identification of the genetic defect the patient was scheduled for hematopoietic stem cell transplantation (HSCT). Here, we present and discuss the diagnostic and therapeutic approach of a novel case of BLS type II in relation to T-cell development.