There is increasing evidence of the contribution of genetic susceptibility to the etiology of Parkinson's disease (PD). Genetic variations in the SNCA gene are well established by linkage and genome-wide association studies. Positive associations of single nucleotide polymorphisms (SNPs) in SNCA and increased risk for PD were found. However, the role of SNCA variants in individual traits or phenotypes of PD is unknown. Here, we reviewed the current literature and identified 57 studies, performed in fourteen different countries, that investigated SNCA variants and susceptibility to PD. We discussed the findings based on environmental factors, history of PD, clinical outcomes, and ethnicity. In conclusion, SNPs within the SNCA gene can modify the susceptibility to PD, leading to increased or decreased risk. The risk associations of some SNPs varied among samples. Of notice, no studies in South American or African populations were found. There is little information about the effects of these variants on particular clinical aspects of PD, such as motor and nonmotor symptoms. Similarly, evidence of possible interactions between SNCA SNPs and environmental factors or disease progression is scarce. There is a need to expand the clinical applicability of these data as well as to investigate the role of SNCA SNPs in populations with different ethnic backgrounds.

An association between Parkinson's disease (PD) and brain-derived neurotrophic factor (BDNF) was suggested by several studies, with contradictory results. BDNF is necessary for the survival of dopaminergic neurons in substantia nigra. Val66Met is a common polymorphism of the BDNF gene that affects cognitive and motor processes. The authors studied 104 Brazilian patients with PD and 96 control participants. The G/G genotype was significantly associated with depression and anxiety symptoms and development of PD. This is the first study that associates this genotype with PD.

Passiflora cincinnata Masters is a Brazilian native species of passionflower. This genus is known in the American continent folk medicine for its diuretic and analgesic properties. Nevertheless, few studies investigated possible biological effects of P. cincinnata extracts. Further, evidence of antioxidant actions encourages the investigation of possible neuroprotective effects in animal models of neurodegenerative diseases. This study investigates the effect of the P. cincinnata ethanolic extract (PAS) on mice submitted to a progressive model of Parkinson's disease (PD) induced by reserpine. Male (6-month-old) mice received reserpine (0.1 mg/kg, s.c.), every other day, for 40 days, with or without a concomitant treatment with daily injections of PAS (25 mg/kg, i.p.). Catalepsy, open field, oral movements, and plus-maze discriminative avoidance evaluations were performed across treatment, and immunohistochemistry for tyrosine hydroxylase was conducted at the end. The results showed that PAS treatment delayed the onset of motor impairments and prevented the occurrence of increased catalepsy behavior in the premotor phase. However, PAS administration did not modify reserpine-induced cognitive impairments. Moreover, PAS prevented the decrease in tyrosine hydroxylase immunostaining in the substantia nigra pars compacta (SNpc) induced by reserpine. Taken together, our results suggested that PAS exerted a neuroprotective effect in a progressive model of PD.