The frequency decline from Southeast China to West and North China is quite smooth. The allele frequencies decrease to less than 20% in Southwest and Central China, and to less than 10% in Manchuria, Mongolia, Xinjiang, and Tibet within the broader region of East Asia. In Central Asia and Siberia, beyond the pronounced genetic influence of Han Chinese, the ALDH2*504Lys allele is rare. The allele is also detected in some Iranian populations, which may be explained by diffusion along the Silk Road. We conclude that the spread of ALDH2*504Lys to the north and west was concomitant with the expansion of Han Chinese and diffusion of the allele into surrounding populations.
