Billion of years ago bacteria is believed to have entered a eukaryotic cell and converted to mitochondria. The respiratory chain present in it supplies ATP to all cells and therefore the diseases can have any phenotype. Diagnosis may be difficult to confirm by the conventional methods including genetics. Two brothers born to consanguineous parents had global delay, mild visual impairment and drooping of eyelids since birth in the elder child and dysmorphism in the second one. Both had progressive myelopathy due to retroflexed odontoid ,large arachnoid cyst and tethered cord. Muscle biopsy with special stain was normal but respiratory chain assay revealed severe complex 1 deficiency.Elder child underwent surgical decompression of the arachnoid cyst with duroplasty with significant improvement.Atlanto axial dislocation and large arachnoid cyst as cause of myelopathy is not reported in literature in patients with respiratory chain disorders to the best of our knowledge.