Genotypic single-point association test results and LD over NRG2, NRG3, EGFR and ERBB2. In the plot of -log10(P) v. map position, horizontal dashed lines are at P = 0.05, 0.01 and 0.001. Vertical dashed lines are at 20 kb intervals. The region covered by the gene is indicated in the centre of the figure by a horizontal line, with an arrow head indicating the direction of transcription. A crossing vertical line indicates the position of each exon.