NOP9 is an essential nucleolar RNA-binding protein that functions as a critical regulator of ribosomal RNA (rRNA) processing. As a PUF-family protein with eleven Pumilio repeats, NOP9 recognizes both structured and single-stranded RNA elements within the 20S preribosomal RNA 1. Its primary function involves preventing premature cleavage by the nuclease Nob1, thereby ensuring correct stepwise processing of pre-18S rRNA to generate mature small ribosomal subunit rRNA 2. NOP9's C-shaped fold allows its amino-terminal module to recognize double-stranded RNA stems while its carboxy-terminal module binds single-stranded regions, exemplifying a novel class of Pumilio repeat proteins 2. Defects in human NOP9 have significant clinical relevance across multiple disorders. Genetic variants in NOP9 are associated with specific language impairment (SLI) and reading disabilities through parent-of-origin effects, with rs4280164 conferring paternal effects on language phenotypes 345. Additionally, NOP9 variants show associations with breast cancer, autoimmunity, and learning/language impairment 1. Recent evidence links NOP9 polymorphisms (rs2332320) to acute graft-versus-host disease susceptibility in pediatric hematopoietic stem cell transplant recipients 6. These findings underscore NOP9's essential role in both fundamental ribosomal biogenesis and neurodevelopmental processes.