MICOS13 (mitochondrial contact site and cristae organizing system subunit 13), also known as QIL1 or C19orf70, is a critical component of the MICOS complex embedded in the mitochondrial inner membrane. It functions as a structural bridge between two MICOS subcomplexes 1, essential for maintaining cristae junction formation and inner membrane architecture 234. MICOS13 is required for incorporating MIC10 into the mature MICOS complex 23; its absence causes MICOS disassembly and abnormal cristae morphology characterized by concentric ring accumulation rather than normal cristae junctions 35. Functionally, MICOS13 deletion impairs mitochondrial respiratory chain function and reduces oxidative phosphorylation capacity 56. Clinically, homozygous MICOS13 mutations cause hepatocerebral mitochondrial DNA depletion syndrome (MTDPS) with early-onset fatal mitochondrial encephalopathy, liver disease, and failure to thrive 786. The GxxxG motif and WN motif within MICOS13 are conserved and essential for membrane insertion, protein stability, and subcomplex bridging 1. MICOS13-deficient fibroblasts show restored respiratory function when wild-type MICOS13 is expressed 73, supporting its therapeutic potential.