Concerning the implication of CNR1 gene polymorphisms in the vulnerability to PD and PD-related depression, Barrero and colleagues (2005) have demonstrated that the length of the triplet (AAT)n of the CNR1 gene was not significantly different between PD patients and controls, as well as between non-PD individuals with and without depression, although the sample size of the depressed non-PD participants was rather small [111]. This evidence concerns the gene CNR1 and major depressive disorder.