Reported by ClinVar to cause Lewy body dementia (https://www.ncbi.nlm.nih.gov/clinvar/variation/7026/). In ClinVar this variant is reported as “pathogenic” (causing this condition) by a single source, OMIM, which cites Ohtake et al 2004 (https://www.ncbi.nlm.nih.gov/pubmed/15365127).
Ohtake et al found this variant in one of 43 patients screened, and hypothesized it causes a “dominant trait with reduced penetrance or a risk factor polymorphism”. The statistical significance of this observation is unclear; this variant is moderately (but not extremely) rare: according to ExAC it is carried by roughly 1 in 1400 individuals (http://exac.broadinstitute.org/variant/5-176048219-G-T). There don’t appear to be any publications since 2004 that have studied affected patients and confirmed Ohtake et al’s hypothesis regarding this gene (SNCB) as a cause of this disease.