The diverse functions of the DnaJ/Hsp40 family in protein folding/unfolding, membrane trafficking, synaptic modulation and mitochondrial function are considered to not only affect the dopaminergic neurotransmission but also concomitantly influence on the PD-related neuropathological changes, such as nigral cell loss and Lewy body formation. The gene discussed is DNAJB1; the disease is Parkinson disease.