Most of the loci with the strongest evidence for association (P < 1 × 10−50) had been previously identified, but two are new (Extended Data Fig. 1 and Supplementary Table 1): one is on the X chromosome, which was not analyzed in previous genome-wide association studies (GWAS), and the other, rs334 in HBB, is a variant known to cause sickle cell disease, which is predominantly seen in individuals with African ancestry. The gene discussed is HBB; the disease is sickle cell disease.