RFXANK, also known as regulatory factor X-associated ankyrin-containing protein, is a key positive regulator of major histocompatibility complex II (MHC II) gene expression [5]. The RFXANK-encoded subunit is involved in the assembly of multiple transcription factors on MHC II promoters, playing a crucial role in antigen presentation and the immune response [6].

Mutations in the RFXANK gene account for over 70% of known patients with MHC II deficiency worldwide [2]. Homozygous loss-of-function mutations in RFXANK can cause bare lymphocyte syndrome (BLS) type II, complementation group B, which is associated with late-onset immunodeficiency and can also lead to progressive neurodegenerative disease including ataxia and neurologic regression [1]. In a multicenter cohort, patients with RFXANK mutations presented with later onset and diagnosis compared to those with RFX5 mutations, along with a more significant diagnostic delay [3]. In Iranian patients, a specific RFXANK founder mutation (c.162delG) was identified, which was limited to the Iranian population and dated back approximately 1296 years ago [4].

In conclusion, RFXANK is essential for the proper expression of MHC II molecules, which is crucial for the immune system's antigen-presenting function. The study of RFXANK gene mutations in various patient populations helps to understand the genetic basis of MHC II deficiency and associated neurodegenerative diseases, providing insights for early diagnosis, prognosis, and potential treatment strategies such as hematopoietic stem cell transplantation [1,2,3,4].