Mutation analysis of the PARKIN, PINK1, DJ1, and SNCA genes in Turkish early-onset Parkinson's patients and genotype-phenotype correlations

Objective: Variations in PARK genes (PRKN, PINK1, DJ-1, and SNCA) cause early-onset Parkinson's disease (EOPD) in different populations. In the current study, we aimed to evaluate the frequencies of variations in PARK genes and the effects of these variations on the phenotypes of Turkish EOPD patients.

Methods: All coding regions and exon-intron boundaries of the PRKN, PINK1, DJ-1, and SNCA genes were screened by heteroduplex analysis followed by direct sequencing of the detected variants in 50 Turkish EOPD patients. These variants were evaluated using SIFT, PolyPhen, HSF, and LOVD web-based programs.

Results: The frequency of EOPD-associated variations in the PRKN gene was 34%. Among these variations, p.A82E in exon 3 and p.Q409X in exon 11 was determined to be pathogenic. We also defined previously unknown cryptic variations, including c.872-35 G>A and c.872-28T>G in exon 8 of PRKN and c.252+30 T>G and c.322+4 A>G in exons 4 and 5 of DJ1, respectively, that were associated with EOPD. Although no significant association was observed between the PARK gene mutations and clinical features (P>0.05), the alterations were related to the clinical symptoms in each patient.

Conclusion: An increasing number of studies report that PRKN, PINK1, DJ1 and SNCA mutations are associated with early-onset Parkinson's disease; however, a limited number of studies have been conducted in Turkey. Additionally, our study is the first to evaluate the frequency of SNCA mutations in a Turkish population. The aim of this study was determine the frequency distributions of the PRKN, PINK1, DJ1, and SNCA gene mutations and to analyze the relationships between these genetic variations and the clinical phenotype of EOPD in Turkish patients.