DGUOK and pathologic nystagmus: DGUOK mutation unbalance the mitochondrial deoxyribonucleoside triphosphate (dNTP) pool which can cause mtDNA synthesis breakdown, eventually cause MDS.[3] The significant clinical presentation of DGUOK mutant MDS patients is liver impairment, or accompanied with epilepsy, hypotonia, ataxia, and nystagmus.