An extremely rare multiple mitochondrial DNA deletion syndrome with markedly decreased deoxyguanosine kinase (DGUOK) activity in skeletal muscle characterized by a highly variable phenotype. Clinical manifestations include progressive external ophthalmoplegia, mitochondrial myopathy, recurrent rhabdomyolysis, lower motor neuron disease, mild cognitive impairment, sensory axonal neuropathy, optic atrophy, ataxia, hypogonadism and/or parkinsonism.