In addition, more than 80 positional and functional candidate gene studies of OCD have been reported, predominantly for variants within genes in the serotonin, dopamine and glutamate26, 27 pathways and within those involved in immune and white matter pathways.28 SLC1A1, which encodes a neuronal glutamate transporter and which is located within the linkage peak on chromosome 9p, is the only candidate gene observed to be associated in multiple independent samples, although the specific associated variant has varied.29-32
