PARK7 and Parkinson disease: However, it is interesting to note that miR-34b, whose downregulation is coupled to a decrease in the expression of DJ1 and Parkin, two proteins associated to familial forms of PD [67], is also up-regulated in response to Huntingtin (mHTT) mutant in both pluripotent and neuronally differentiated human cells and in human plasma, suggesting a miR-34b role as biomarker for HD [66].