microRNAs involved in Parkinson's disease: A systematic review

The aim of the present study was to determine the expression of blood microRNAs (miRNAs) involved in PD in humans. For this purpose the following electronic databases were selected: MEDLINE by Pubmed, Scopus and Web of Science. The search strategy included the proposed descriptors in the Medical Subject Headings. There were no restrictions with respect to the language of the publication. In the study selection two independent reviewers initially evaluated studies that were identified by the search strategy according to titles and abstracts. The reviewers evaluated (also unassisted) the complete articles and selected studies according to the eligibility criteria specified above. Studies that were not in accordance with the adopted criteria were excluded according to the boundaries imposed by the search strategy. The following data were extracted from the selected studies: Publication identification, location where the study was conducted, study design, the sample size, the participants' characteristics, the miRNAs involved in PD, the miRNA detection and analysis method, and the type of miRNA dysregulation in PD. Through this systematic review of the literature published over the last 10 years, the expression of 91 different miRNAs were analyzed in the context of PD, with the expression of 39 of these miRNAs differing significantly between individuals with PD and healthy controls and/or between treated and untreated patients with PD. The miRNAs were extracted from mononuclear cells, leukocytes, plasma, serum and peripheral blood, and the majority of the studies used reverse transcription-quantitative polymerase chain reaction (RT-qPCR), which is considered to be the gold standard for miRNA analysis.