The present invention provides a diagnostic method and a kit for detection of mutations localized within the 5′ promoter region of the MnSOD gene. Such mutations are associated with diseases characterized by decreased MnSOD activity such as certain formes of cancer, and ALS. Accordingly, the diagnostic method this invention provides, comprising RFLP, direct sequencing, or PCR analysis of the region within 3 kb, the transcription initiation site will detect these disorders. This invention also provides a therapeutic method for such disorders comprising transfection of affected cells or tissues with high activity, MnSOD expression vectors, or the administration of exogenous MnSOD enzyme
