No association of endocannabinoid genes with bipolar disorder or lithium response in a Sardinian sample

Bipolar disorder (BD) is a chronic and severe psychiatric condition with an underlying component of genetic susceptibility. Mounting evidence suggests a potential role of the endogenous cannabinoid (eCB) system in the pathogenesis of BD. Here we investigated the role of genes encoding for key eCB elements on the risk of developing BD in a sample of 357 BD patients and 422 healthy controls of Sardinian ancestry. Using the HapMap CEU population SNP database, we selected 25 tag Single Nucleotide Polymorphisms (tSNPs) in N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD), cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH) genes. No significant association was reported for FAAH or CNR1. SNPs rs11487077 and rs6465903 in NAPE-PLD showed nominal association (p=0.033 and p=0.026, respectively) with BD, not significant after permutation testing. These SNPs were also tested for association with lithium response in 204 BD patients characterized for response to long-term lithium treatment, reporting no significant findings. As a whole, our results do not support a clear role of FAAH, CNR1 and NAPE-PLD in BD and lithium response. Additional studies on independent, larger samples are warranted to further explore the involvement of the eCB system in BD.