Genetic Variants in SNCA and the Risk of Sporadic Parkinson’s Disease and Clinical Outcomes: A Review

Table 4

Association of clinical aspects of PD and SNPs within SNCA.

Variables	Studies	Results
Age at onset	[28, 32, 35, 37, 40, 41, 46, 53, 54, 58, 66, 69, 70, 72, 79]	SNPs were associated with earlier PD onset: REP1-263 bp [35, 69, 79]; C-rs2736990 [41]; G-rs894278 [35]; G-rs356219 [46, 53, 58]; G-rs356215 [54]
Motor outcomes	[28, 31, 32, 34, 43, 50, 51, 74]	Wang et al. [31] found a protective association between T-rs11931074 allele carriers and motor severity. Ritz et al. [50] found that REP1-263 bp and G-rs356165 alleles increased the risk of faster decline of motor function, whereas Markopoulou et al. [43] demonstrated that REP1-263 bp allele reduced the risk of developing motor impairments
Cognition outcomes	[31–34, 37, 40, 42, 43, 74, 78]	Markopoulou et al. [43] showed an increased risk of cognitive impairment in carriers of REP1-259 bp allele. Guella et al. [33] found a significant association of C-rs10018362, T-rs7689942, and G-rs1348224 alleles with PD with dementia
Anxiety and depression	[32, 34, 37, 40, 74]	No SNPs were significantly associated with symptoms
Autonomic and sleep disorders	[34, 74]	No SNPs were significantly associated with symptoms
Hyposmia	[34, 74]	In Chen et al.’s study [34], TT-rs11931074 genotype increased the risk of hyposmia in PD

See Table 1. Questionnaires used: Unified Parkinson Disease Rating Scale-III and Hoehn and Yahr. Questionnaires used: Mini-Mental State Examination, Frontal Assessment Battery, Montreal Cognitive Assessment, Scales for Outcomes in Parkinson’s Disease Cognition, Hopkins Verbal Learning Test-Revised, Letter-Number Sequencing Test and Trail Making Test, Semantic and Phonemic Verbal Fluency Tests, and Benton Judgment of Line Orientation test. Questionnaires used: Hamilton Rating Scale for Depression and Anxiety and Beck Depression Inventory. Questionnaires used: REM Sleep Behavior Disorder Questionnaire, and Scales for Outcomes in Parkinson’s Disease Autonomic, Nighttime Sleep, Daytime Sleepiness and Psychiatric Complications.