I56i enhancer activity is impaired by the 182-SNP in the adult cortex. Quantification of the percentage of lacZ-expressing cells that co-express various GABAergic interneuron subtypes (PV, parvalbumin; SOM, somatostatin; CB, calbindin; CR, calretinin) in the adult mouse somatosensory cortex at P35. The contribution of vI56i-lacZ-expressing precursors to adult cortical interneuron populations expressing PV, SOM, CB and CR was significantly reduced compared with that of I56i-lacZ-expressing cells. All data are presented as mean ± s.e.m. *, P<0.001.