MRPS23 encodes a mitochondrial ribosomal protein S23, a component of the mitochondrial ribosome small subunit involved in mitochondrial translation. As a nuclear-encoded mitochondrial protein, MRPS23 localizes to the mitochondrial inner membrane where it participates in protein synthesis 1. Primary function: MRPS23 is essential for mitochondrial oxidative phosphorylation (OXPHOS). Mutations in MRPS23 cause combined oxidative phosphorylation deficiency through impaired mitochondrial translation, leading to respiratory chain complex deficiencies 2. Disease relevance: MRPS23 is established as a causative gene for autosomal recessive mitochondrial disorders presenting with altered consciousness, vomiting, growth delay, hearing impairment, hypoglycemia, lactic acidosis, and liver dysfunction 2. The homozygous p.P40L variant in MRPS23 causes combined respiratory chain complex deficiency with low activities of complexes I and IV in cultured fibroblasts 2. Clinical significance: Beyond mitochondrial disease, MRPS23 shows oncogenic functions. The protein is frequently amplified and overexpressed in breast cancer, correlating with higher proliferation and non-basal subtypes 3. In glioma, elevated MRPS23 expression independently predicts poor overall survival, disease-free survival, and progression-free survival 4. Post-translational modifications—including CDK11-mediated phosphorylation and arginine/lysine methylation—regulate MRPS23 stability and affect cancer cell proliferation and metastasis 56.