DNAJC21 is a heat shock protein family member functioning as a co-chaperone that plays critical roles in ribosomal RNA biogenesis and ribosome maturation. It binds precursor 45S rRNA and stabilizes the 80S ribosome during the maturation of the 60S subunit 1. At the molecular level, DNAJC21 acts as a co-chaperone for HSP70 and is involved in protein folding within the cytoplasm and nucleolus 1. Biallelic DNAJC21 mutations cause bone marrow failure syndrome 3 (BMFS3), a ribosomopathy characterized by inherited bone marrow failure 23. Patients present with early-onset cytopenia, thrombocytopenia, and variable extrahematopoietic features including dysmorphic findings and developmental delay 4. The condition shows clinical overlap with other ribosomopathies such as Shwachman-Diamond syndrome 1. Recent evidence suggests DNAJC21 may also influence immune regulation: genetic variants associate with increased immune thrombocytopenia (ITP) risk, with DNAJC21 protein potentially upregulating CD36 expression to modulate platelet counts 56. However, current treatment options remain limited to bone marrow transplantation, with no gene-based therapies yet developed 1.