In neurodegenerative post-mortem studies, reduction of serotonergic neurons has also been observed; loss of medullary raphe TPH2 neurons has been shown in multiple system atrophy and in Parkinson’s disease with Lewy bodies and proposed as relevant to the sleep-related disordered breathing occurring in these conditions (Presti et al., 2014). The gene discussed is TPH2; the disease is sleep apnea syndrome.