A patient with RFX5 variant causing an expression defect in both HLA ABC and HLA DR

The major histocompatibility complex (MHC) encompasses a group of genes critical for immune system regulation. In humans, these molecules are referred to as human leukocyte antigens (HLA) due to their initial discovery in human leukocytes. Class I molecules present antigens to CD8 + T cells, while Class II molecules present to CD4 + T cells. Here we report a patient who had a background of parental consanguinity and a family history suggestive of immunodeficiency. He presented with clinical symptoms including fever, septic arthritis, recurrent moniliasis. Preliminary diagnostic tests revealed hypogammaglobulinemia and CD4 lymphopenia. Further immunological assessment indicated extremely low expression levels of HLA molecules: HLA ABC at 5% and HLA DR at 0%. Genetic analysis showed a mutation in the regulatory factor X5 (RFX5) gene, leading to a combined immunodeficiency diagnosis. Consequently, hematopoietic stem cell transplantation (HSCT) was planned. Regulatory factor X5plays a pivotal role in immune function by transactivating genes critical for the expression of MHC Class I and Class II molecules, as well as beta- 2-microglobulin (B2M). MHC Class I transcription is controlled indirectly by RFX5, and the RFX5 gene mutation in the patient likely caused the markedly reduced expression of HLA ABC in addition to HLA DR. Combined HLA-ABC and HLA-DR expression analyses via flow cytometry may serve as a valuable diagnostic tool for identifying RFX5-related immunodeficiency at an early stage, facilitating timely genetic testing and appropriate clinical management.

Clinical, Immunological, and Genetic Findings in Iranian Patients with MHC-II Deficiency: Confirmation of c.162delG RFXANK Founder Mutation in the Iranian Population

PURPOSE

Major histocompatibility complex class II (MHC-II) deficiency is a rare inborn error of immunity (IEI). Impaired antigen presentation to CD4 + T cells results in combined immunodeficiency (CID). Patients typically present with severe respiratory and gastrointestinal tract infections at early ages. Hematopoietic stem cell transplantation (HSCT) is the only curative therapy.

METHODS

We describe the clinical, immunologic, and genetic features of eighteen unrelated Iranian patients with MHC-II deficiency.

RESULTS

Consanguinity was present in all affected families. The median age at the initial presentation was 5.5 months (range 7 days to 18 years). The main symptoms included failure to thrive, persistent diarrhea, and pneumonia. Autoimmune and neurologic features were also documented in about one-third of the patients, respectively. Thirteen patients carried RFXANK gene mutations, two carried RFX5 gene mutations, and three carried a RFXAP gene mutation. Six patients shared the same RFXANK founder mutation (c.162delG); limited to the Iranian population and dated to approximately 1296 years ago. Four of the patients underwent HSCT; three of them are alive. On the other hand, nine of the fourteen patients who did not undergo HSCT had a poor prognosis and died.

CONCLUSION

MHC-II deficiency is not rare in Iran, with a high rate of consanguinity. It should be considered in the differential diagnosis of CID at any age. With the limited access to HSCT and its variable results in MHC-II deficiency, implementing genetic counseling and family planning for the affected families are mandatory. We are better determined to study the c.162delG RFXANK heterozygous mutation frequency in the Iranian population.