Identification of single nucleotide polymorphisms (SNPs) within protein genes linked to the transition from individuals genetically predisposed to Parkinson's disease (PD) but asymptomatic (GUN) to those displaying symptoms of the disease (GPD).

Some of the SNPs are up-represented in GPD individuals, suggesting that they may have a role in the manifestation of Parkinson's disease, possibly through the "combination" of SNPs

The SNPs present in the fatty acids, eicosanoids, vitamins, and sterols metabolisms seem to have a better effect in the switch from GUN to GPD individuals.

Endogenous factors, such as inflammation, vitamin D metabolism, and cholesterol degradation and pathways, appear to be crucial factors in triggering the onset of Parkinson's disease symptoms.

In addition to harmful single nucleotide polymorphisms (SNPs) that are significantly more prevalent in patients with symptomatic Parkinson's disease (GPD), protective SNPs are equally significant. These protective SNPs, largely absent in GPD patients, are present in those who are genetically predisposed to Parkinson's disease but asymptomatic (GUN). The potential protective effect could play a significant role in slowing the progression of Parkinson's disease.

Identification of 7 SNPs and AdR with no significant differences

Identification of 3 cytochromes P450 with OR>10 (CYP4V2, CYP24A1, CYP39A1)

SNPs(GPD/GUN) < SNPs(GUN/HC) and SNPs(GPD/HC)

SNPs with OR>5

Metabolisms: fatty acids, eicosanoids, vitamins, sterols

SNPs with OR<0.2

Metabolisms: fatty acids, eicosanoids, vitamins, sterols, drugs and xenobiotics

No SNPs over-represented (OR>5)

No SNPs with OR<0.2

1 SNP with 2.0<OR<5.0

SNPs with OR>5 (CYP7B1, CYP39A1)

6 SNPs with 2.0<OR<5.0 (CYP46A1)

High-OR SNPs with unknown function

SNPs with OR>5 (CYP24A1, CYP26B1, CYP27C1)

5, 3 and 26 SNPs with 2.0<OR<5.0

SNP highly protective (OR<0.2, CYP27C1)

No SNPs with OR>5

Except 7 of the total cytochromes P450 (CYP1A1, CYP1A2, CYP2A6, CYP2C8, CYP2C18, CYP2F1, CYP3A4) do not have 2.0<OR<5.0

SNPs with OR<0.2 (CYP2C8)

SNPs with OR>5 (CYP4F3, CYP4F8, CYP8A1)

SNPs with 2.0<OR<5.0 (CYP4F2, CYP4F3, CYP5A1, CYP8A1)

82 SNPs with 0.2<OR<0.5

2 SNPs with OR>5 (modifier function)

2 SNPs with 2.0<OR<5.0

57 SNPs with 0.5<OR<2.0

Up-represented in GPD and HC individuals

Important SNPs (CYP5A1, CYP2C8, CYP4F3, CYP4B1, POR)

Cytochrome P450 with a protective effect (SNPs with OR<1)

“Rolf M. Schwiete Stiftung” Center in Mannheim/Germany and PPMI database: the research was granted by the center and was made possible through the access of data from the Parkinson’s Progression Markers Initiative (PPMI) database, wich has been supporting investigations worldwide.

PPMI data and Bioinformatics: the extraction and classification of the data from the PPMI database was performed by Prof. Dr. Andreas Keller and Dr. Tobias Fehlmann from Saarland clinical informatics campus, in cooperation with the research team.

Interdisciplinary research team consortia: the design, analysis and discussion of project data and results were performed by team members organized for different contributions.

The R project for statistical computing: programming language used for gene variants classification groups in this research ensured high-quality data.

SnpEff and SnpSift 5.0: rapidly categorizing the effects of variants in genome sequences based on their genomic locations and predicts coding effects.

Software IBM® SPSS®: advanced statistic analysis. Suitable for projects of all sizes and levels of complexity.

Parkinson's Progression Markers Initiative (PPMI) - obtain complete sequencing data for the genomes of P450, P450 reductase (POR), adrenodoxin (Adx), adrenodoxin reductase (AdR), and their genetic variants.

All authors declared that the research was conducted without any commercial or financial affiliations that might pose a potential conflict of interest.

However, there’s no evident sign of a speciallized committe’s authentication on the fulfillment of the social and ethical laws on this article.

CYP2D6, CYP2C9 and CYP3A4 show OR values between 1.4 and 2.9, while CYP2A6 and CYP2F1 display protective SNPs with OR < 1, in both GPD/HC and GPD/GUN.

Special attention should be given to CYP2C8, which displays 10 SNPs, though with moderate OR values, which are found in GPD/GUN and also in GPD/HC.

Summarizing, this suggests that toxic compounds, e.g., pesticides, seem to be of rather moderate importance for the manifestation of PD in genetically predisposed individuals.

CYP4V2 shows a SNP with OR = 10.02 in GPD/GUN. It also shows two protective SNPs, that are under-represented in GPD/GUN and GPD/HC.

CYP4V2 is widely expressed in different organs and tissues, also in brain, and is described to show ω-hydroxylase activity on saturated and polyunsaturated fatty acids (PUFAs) of medium and long chain length.

A functional impairment of CYP4V2 leads to a malfunction of global lipid metabolism. Causing Reduction in the transformation of fatty acid precursors into w-3 PUFAs and decreased synthesis of eicosapentaenoic (EPA)(20:5) and docosahexaenoic acids (DHA)(22:6).

In view of the involvement of CYP4V2 in the metabolism of saturated and polyunsaturated fatty acids, we checked whether the consumption of fish oil and omega fatty acid supplements has an effect on the manifestation of GPD since for some individuals in the PPMI database corresponding information is available. Analysis of the data, however, didn't show any statistical significance, thus demonstrating no protective role of the oil on the manifestation of the disease.

Analyzing the role of P450s of the “eicosanoid” group, our results show that P450s involved in eicosanoid metabolism and inflammation seem to have a key function in the manifestation of GPD.

CYP4F2, CYP4F3, CYP5A1 and CYP8A1 have SNPs with OR values between 2 and 5 in GPD/GUN and GPD/HC.

CYP5A1 is a tromboxane synthase and its function is related to the action of CYP8A1, a prostacyclin synthase. While both P450s use prostaglandin H2 (PGH2) as a substrate, prostacyclin (prostaglandin I2, PGI2), resulting from the catalytic action of CYP8A1, causes vasodilation, inhibits platelet aggregation. While thromboxane A2 (TXA2), resulting from the catalytic action of CYP5A1, causes vasoconstriction, promotes platelet aggregation.

The balance of the two products affects important physiological processes such as blood pressure regulation, blood coagulation and inflammation.

CYP24A1 is one of the three P450s displaying a SNP with OR = 10.02 for GPD/GUN.

The SNP is located in an intron region and suggested to behave as a modifier of function. It is responsible for the degradation of 25OH- as well as 1α, 25- dihydroxy vitamin D3 to 24-hydroxylated products.

Changes in the expression and functionality of CYP24A1 may thus have broad consequences. First, malfunction could lead to an accumulation of the precursor 7- dehydrocholesterol and in this way to increased levels of cholesterol. On the other hand, an unbalanced high expression of CYP24A1 may lead to vitamin D deficiency thereby causing various disorders connected to bone metabolism, immunomodulation and proliferative disorders like cancer.

There is no effect of nutritional supplementation with vitamin D on the manifestation of PD in genetically pre-disposed individuals.

Sterol-converting P450s also show a strong association of SNPs in corresponding P450 genes with the manifestation of PD in GPD vs. GUN.

CYP39A1 is the third P450 found in our studies with an OR = 10.02 (GPD/GUN). This P450 plays a prominent role in the degradation of cholesterol. By using GWAS investigations it was reported that four intron variants of CYP39A1 (rs6907129, rs6905960, rs7749491, rs16874881) are strongly associated with the occurrence of levodopa-induced dyskinesia in patients aged over 50 years at the onset of PD.

CYP7B1 is another P450 gene having SNPs with OR values >5 in GPD/GUN. This P450 is also involved in the degradation of cholesterol leading to 7α-hydroxylation of 27-hydroxycholesterol.

CYP20A1 belongs to the group of “orphan” P450s, displays SNPs with OR > 5 (GPD/GUN).

CYP20A1 is especially abundant in S. nigra and the hippocampus of human brain.

Thus, endogenous rather than exogenous factors seem to be responsible for the differentiation between GPD and GUN and inflammation, vitamin D metabolism, cholesterol degradation and pathways affected by CYP20A1 seem to be key players in eliciting PD manifestation.

POR show SNPs with OR > 5 when comparing all SNPs between GPD and GUN.

Shows SNPs with OR < 0.2 in both approaches indicating on a contribution of this protein, which is the redox partner of all microsomal P450s, for the transformation from GUN to GPD.

This points to a possible modulatory effect of this redox partner on the manifestation of PD in GPD patients.