C2orf69 mutations disrupt mitochondrial function and cause a multisystem human disorder with recurring autoinflammation

Deciphering the function of the many genes previously classified as uncharacterized "open reading frame" (orf) completes our understanding of cell function and its pathophysiology. Whole-exome sequencing, yeast 2-hybrid and transcriptome analyses together with molecular characterization are used here to uncover the function of the C2orf69 gene. We identified loss-of-function mutations in the uncharacterized C2orf69 gene in eight individuals with brain abnormalities involving hypomyelination and microcephaly, liver dysfunction and recurrent autoinflammation. C2orf69 contains an N-terminal signal peptide that is required and sufficient for mitochondrial localization. Consistent with mitochondrial dysfunction, patients showed signs of respiratory chain defect and a CRISPR-Cas9 knockout cell model of C2orf69 had similar respiratory chain defects. Patient-derived cells revealed alterations in immunological signaling pathways. Deposits of PAS-positive material in tissues from affected individuals together with decreased glycogen branching enzyme 1 (GBE1) activity indicated an additional impact of C2orf69 on glycogen metabolism. Our study identifies C2orf69 as an important regulator of human mitochondrial function and suggests an additional influence on other metabolic pathways.