Mutation of TWNK Gene Is One of the Reasons of Runting and Stunting Syndrome Characterized by mtDNA Depletion in Sex-Linked Dwarf Chicken.

Runting and stunting syndrome (RSS), which is characterized by low body weight, generally occurs early in life and leads to considerable economic losses in the commercial broiler industry. Our previous study has suggested that RSS is associated with mitochondria dysfunction in sex-linked dwarf (SLD) chickens. However, the molecular mechanism of RSS remains unknown. Based on the molecular diagnostics of mitochondrial diseases, we identified a recessive mutation c. 409G > A (p. Ala137Thr) of Twinkle mitochondrial DNA helicase (TWNK) gene and mitochondrial DNA (mtDNA) depletion in RSS chickens' livers from strain N301. Bioinformatics investigations supported the pathogenicity of theTWNKmutation that is located on the extended peptide linker of Twinkle primase domain and might further lead to mtDNA depletion in chicken. Furthermore, overexpression of wild-typeTWNKincreases mtDNA copy number, whereas overexpression ofTWNKA137T causes mtDNA depletionin vitro. Additionally, theTWNKc. 409G > A mutation showed significant associations with body weight, daily gain, pectoralis weight, crureus weight, and abdominal fat weight. Taken together, we corroborated that the recessiveTWNKc. 409G > A (p. Ala137Thr) mutation is associated with RSS characterized by mtDNA depletion in SLD chicken.