Hypocretin (orexin) and melanin concentrating hormone loss and the symptoms of Parkinson's disease

We reported that Parkinson's disease (PD) patients have a substantial loss of hypocretin (Hcrt) cells (Thannickal et al. , 2007). As two of the authors of the letter to which we are responding have emphasized in their prior publication (Baumann et al. , 2005), and as other groups have reported, the sleep disturbances associated with PD are a major complaint in a large proportion of these patients (Arnulf et al. , 2000; Frucht et al. , 2000; Arnulf et al. , 2002; Frucht, 2002; Onofrj et al. , 2003; Arnulf, 2005; Abbott et al. , 2005; Arnulf, 2006; Benbir et al. , 2006; Rye, 2006; Savitt et al. , 2006) and resemble the sleep complaints of narcoleptics. These disturbances can include not only sleep attacks and nocturnal insomnia, but also REM sleep behaviour disorder, which can lead to severe injury.In our prior study of narcoleptics, the loss of Hcrt cells, in patients who had been symptomatic for an average of 41 years (range 31–51 years), was on average 91% (range from 86 to 94%) (Thannickal et al. , 2000). Published data have not …