SLC6A1 and schizophrenia: Two studies of parvalbumin cell density in the frontal cortex showed large effect sizes, those by Hashimoto et al. (2003) and Bitanihirwe and Woo (2014); the latter uniquely used a cRNA GAT-1 probe and a DIG-labelled PV mRNA probe to measure the density of neurons expressing both parvalbumin and GABA transporter 1 (GAT-1) mRNA in cortical layers 3 and 4 (data included in this meta-analysis) in patients with schizophrenia.