The SNCA gene encodes alpha-synuclein, an abundant brain protein known as a pre-synaptic chaperone. Different variants in SNCA have been associated with Alzheimer's disease, Parkinson's disease, and alcoholism.
Of note, a significant variation that is not a SNP in the SNCA gene is a complex repeat polymorphism known as REP1 (D4S3481), located about 10 kb upstream from the SNCA translation start site. REP1 is essentially triallelic and in comparison to the intermediate-length allele (“261”), the longest allele ("263") is associated with increased risk and the shortest ("259") with decreased risk for Parkinson's disease.[PMID 16896109]
Be aware that other publications name the REP-1 alleles a bit differently; for example, [PMID 11156617] names five known alleles with a varying number of dinucleotide repeats ranging in size from the shortest ("265") to the longest ("273").
Low levels of SNCA might offer less protection against oxidative stress [PMID 22936601], whereas high levels of SNCA may have a role in neurodegenerative diseases such as Parkinson's disease. This has led to at least one hypothesis stating that whereas low levels of SNCA may predispose to cravings for alcohol and consequent alcoholism, excessive alcohol consumption then increases SNCA expression greater than in nondrinkers, increasing risk for neurodegenerative diseases in at-risk individuals with SNPs predisposing to its aggregation.[PMID 24844177]
Distinct from REP1, SNCA SNPs have also been associated with the medical conditions already mentioned.
[PMID 25806429] The effect of music performance on the transcriptome of professional musicians.