POLR1H encodes RNA polymerase I subunit H (RPA12), a core component of RNA polymerase I (Pol I) that synthesizes ribosomal RNA precursors 1. As an essential built-in transcription factor, POLR1H is critical for high transcriptional efficiency of Pol I 1. The protein anchors into the Pol I active site to monitor transcription fidelity and cleave mis-incorporated 5'-ribonucleotides, thereby mediating proofreading of nascent RNA transcripts. POLR1H subunits are conserved across diverse organisms, including intestinal parasites such as Giardia duodenalis, Cryptosporidium parvum, and Entamoeba histolytica, suggesting fundamental importance in ribosome biogenesis 2. Functionally, POLR1H participates in transcription initiation, elongation, and termination at Pol I promoters and is involved in nucleolar large rRNA transcription. In human genetics, POLR1H exhibits the largest number of genome-wide association study (GWAS) signal-expression quantitative trait loci (eQTL) pairs among RNA polymerase I genes, indicating extensive impact on complex human traits 1. This genetic variation highlights POLR1H's importance as a potential molecular link between individual genetic differences and phenotypic variation in human populations.