Reported by ClinVar to cause Fatal familial insomnia and Jakob-Creutzfeldt disease (http://www.ncbi.nlm.nih.gov/clinvar/variation/13399/). In ClinVar, it is reported as ““pathogenic”“ by OMIM. OMIM’s submission refers to 13 publications related to this variant: https://www.ncbi.nlm.nih.gov/pubmed/1671983,1684756,1353341,1439789,1469441,1671440,9751723,7709737,1353342,19038218,12205650,16227536,1353344
Various publications report the variant in unrelated families. In addition, Goldfarb et al 1992 (https://www.ncbi.nlm.nih.gov/pubmed/1353341) reports that the position neighboring this genetic variant affects the presentation of disease; they report that Val129 is associated with FFI, while Met129 is associated with hereditary JCD.