This result must therefore be interpreted with particular caution; the association between SNPs in the BDNF gene area and schizophrenia may reflect a causal association between smoking initiation and schizophrenia, but could also potentially be a pleiotropic effect, either via one of the already identified alternative pathways such as obesity or caffeine, or via another currently unidentified pathway. Here, BDNF is linked to obesity due to melanocortin 4 receptor deficiency.