- Mutation of the linker region of the polymerase gamma-1 (POLG1) gene associated with progressive external ophthalmoplegia and Parkinsonism. Hudson, G., Schaefer, A.M., Taylor, R.W., Tiangyou, W., Gibson, A., Venables, G., Griffiths, P., Burn, D.J., Turnbull, D.M., Chinnery, P.F. Arch. Neurol. (2007)