Origin of Tibeto-Burman speakers: evidence from HLA allele distribution in Lisu and Nu inhabiting Yunnan of China.

The issue about the origin of the Tibeto-Burman speaking ethnic groups (TBs) mostly residing in the Hengduan and Himalayan region in southwest China has been disputed for several decades. Based primarily on historical literatures and archaeologic findings the "Di-Qiang origin" hypothesis was proposed, in which the Tibeto-Burman speakers were thought to be descendants of the ancient Di-Qiang groups (DQs) who originated in northwest China. However, other evidence also challenge this hypothesis. In the present study, we investigate the distribution of HLA class I and class II genes in Lisu and Nu, two Tibeto-Burman-speaking ethnic groups, using a high-resolution polymerase chain reaction-sequencing-based typing method. Lisu and Nu share similar allele and haplotype frequencies of HLA class I and class II genes. Phylogenetic trees and principal component analysis based on HLA allele frequencies clearly indicated that Lisu and Nu clustered together with high bootstrap value, suggesting their close genetic relationship. The complicated genetic background of TBs was also revealed. The dendrogram based on HLA class II allelic frequencies demonstrated that East Asians clustered together and that four Tibeto-Burman-speaking ethnic groups (Naxi, Lahu, Lisu, and Nu) formed a clade clustering with southern East Asians (SEA), whereas another Tibeto-Burman speaker, Yi, integrated into the cluster of northern East Asians (NEA). Principal component analysis based on HLA class II allelic frequencies supported that TBs could be classified into two groups with Naxi, Lahu, Lisu and Nu scattering among SEA, while Yi locating close to NEA. A clear boundary between NEA and SEA was also observed in the principal component plot based on HLA class I allele frequencies and Lisu and Nu clustered into the SEA. In conclusion, our results provide evidences that not only DQs but also southwest aborigines may be ancestors of the TBs.