Preclinical signs of Parkinson's disease: A possible association of Parkinson's disease with skin and hair features.

Parkinson's disease (PD) is a neurodegenerative disorder, characterized by loss of dopaminergic neuromelanin containing neurons in the substantia nigra. Peripheral melanin, found in skin and hair, and neuromelanin appear to have some characteristics in common and share the same precursor for their synthesis; therefore, skin and hair features could be associated with PD. We hypothesize that earlier age at onset of hair greying, greater tendency to sunburn, difficulty tanning and dysregulation of sebum production are more common among PD patients due to genetically determined lower constitutive amounts of melanin and accumulation of α-synuclein in the skin, which leads to disrupted synthesis of peripheral melanin and dysregulated sebum secretion. In order to test this hypothesis 32 PD patients and 35 age and gender matched PD-unaffected individuals were included in a pilot study. The median of age at onset of hair greying was 30% lower in the PD group compared to the control group (35 and 50 years, respectively, p = 0.002). Age at onset of hair greying ≤ 41 years predicted the development of PD with 71.0% sensitivity and 70.6% specificity (area under curve = 0.725, 95% confidence interval = 0.601-0.850, p = 0.002). Significant differences were found when comparing skin types between PD patients and the control group (p < 0.001): dry (n = 14, 43.8%) and oily (n = 9, 28.1%) skin types were the most prevalent among individuals with PD, whereas the majority of control subjects reported having normal skin (n = 24, 68.6%). Differences in tanning ability were also found between the groups (p = 0.035): the majority of individuals in the control group (n = 24, 68.6%) and only 12 (37.5%) PD patients reported being able to tan easily. PD patients were also more likely to burn often in comparison to control subjects (n = 21, 65.6% vs n = 10, 28.6%, p = 0.001). Our results support the hypothesis that PD is associated with earlier age at onset of hair greying, greater tendency to sunburn, difficulty tanning and non-normal skin type; however these ideas should be evaluated in a large prospective study in order to draw final conclusions. If such work supports our hypothesis, skin and hair features could be included in a risk-score model to identify individuals at high risk of PD in order to diagnose patients prior to the manifestation of motor symptoms and initiate potential neuroprotective treatment when neuronal loss is minimal.