In both low and high IgG PD patient subgroups a reduced proportion of CD57+ cells in the CD56− T cell subset compared to low and high IgG HD subgroups was observed (6.9 vs. 13.6, p = 0.02; 9.3 vs. 15.9, p = 0.01, respectively). Here, NCAM1 is linked to Parkinson disease.