Similarly, a study screened 600 cases of DOA where prior genetic testing for known causes of optic atrophy (WFS1, OPA1, OPA3, and mitochondrial DNA for the three most common LHON variants) was negative, and a total of seven cases exhibited SPG7 mutations without any of the typical neurologic signs of HSP [25]. This evidence concerns the gene SPG7 and hereditary spastic paraplegia.