Doppler et al. [18] found alpha-synuclein deposition in cutaneous nerves of PD patients and speculated that both retrograde axonal degeneration due to impaired axonal transport and anterograde degeneration due to sensory neuronal cell death may lead to peripheral neuropathy and suggested that skin biopsy might be a useful diagnostic test for PD. This evidence concerns the gene SNCA and peripheral neuropathy.