Plasma levels of α-synuclein — aggregates of which are the pathological hallmark of Parkinson disease (PD) — are increased in patients with obstructive sleep apnoea syndrome (OSAS) and correlate with the degree of hypoxia, according to a new study. Sun et al. measured total and phosphorylated α-synuclein levels in 42 patients with OSAS and 46 age-matched and gender-matched controls who had simple snoring. Total and phosphorylated α-synuclein levels were significantly higher in patients with OSAS than in controls and correlated positively with the apnoea–hypopnoea index and the oxygen desaturation index. Total and phosphorylated α-synuclein levels were negatively correlated with mean and lowest oxyhaemoglobin saturations. Previous studies suggest that OSAS is a risk factor for onset of PD; the authors say their findings indicate that chronic hypoxia increases α-synuclein levels and might be involved in the pathogenesis of PD.