On page 6556 in the 15 December 2011 issue, Figure 2 was accidentally presented in an incorrect format, which resulted in difficulty in viewing the data clearly. Furthermore, the labels for genotypes in Figure 2A were blacked out. The errors do not affect any of the results or conclusions of the study. The corrected Figure 2 is shown. The errors have been corrected in the online version, which now differs from the print version.