Abstract: The present invention provides a method for diagnosing a neurodegenerative disease or for determining the predisposition of a subject to a neurodegenerative disease. In particular, the methods of the present invention comprise detecting a marker linked to map position 9p21, e.g., a marker within an opioid receptor sigma 1 (OPRS1) gene or an expression produce thereof. The present invention also provides a method for identifying new markers that are associated with a neurodegenerative disease. The present invention also provides mutant forms of an OPRS1 gene or an expression product thereof and reagents for detecting those mutations.