However, to gain a more comprehensive understanding of the alteration in B lymphocytes and B lymphocyte subsets in peripheral blood of PD patients, in addition to flow cytometry, studies using other techniques [such as single-cell RNA-seq and the epigenetic clock (based on the DNA methylation levels)] to identify and describe the alteration in B lymphocytes and B lymphocyte subsets in peripheral blood of PD patients were also included in our study; (3)As is well known, it is difficult to infer causality from case-control studies. This evidence concerns the gene CLOCK and Parkinson disease.