PUS3 (pseudouridine synthase 3) is a tRNA-modifying enzyme that catalyzes pseudouridylation at positions 38/39 in the anticodon stem-loop of transfer RNAs 1. The enzyme functions as a symmetric homodimer that recognizes tRNA substrates and positions target uridine residues for isomerization 1. Biochemical studies confirm PUS3 specifically modifies tRNAs but not mRNAs in human cells 1. Biallelic PUS3 variants cause rare neurodevelopmental disorders characterized by global developmental delay, epilepsy, hypotonia, and microcephaly 2. Disease-causing mutations impair protein thermostability or cause aggregation, leading to reduced PUS3 protein levels and diminished pseudouridine modifications in patient-derived cells 3. The clinical spectrum extends to include retinal dystrophy, cerebellar hypoplasia, and cardiac defects in severe cases 4. Recent evidence suggests PUS3 dysregulation participates in sepsis pathogenesis, with elevated PUS3 expression identified as a diagnostic biomarker (AUC 0.834) in septic patients 5. The connection between impaired tRNA modification and intellectual disability demonstrates that accurate tRNA biogenesis is essential for normal brain development.