Based on limited published evidence, H4C9 encodes histone H4, a core component of the nucleosome octamer essential for DNA packaging and chr6 organization. H4C9 supports fundamental cellular processes including DNA replication, transcription, and repair 1. De novo missense variants in H4C9 cause a neurodevelopmental syndrome characterized by intellectual disability and developmental delay, with mutations clustering in the H4 core domain affecting histone-histone and histone-chaperone interactions 1. Additionally, H4C9 RNA was identified as an HIV-1 protein interaction partner involved in viral replication 2.