Thursday, 14 August 2014

A Denisovan signature in modern Tibetans

Tibetan family attending a horse festival (CC) Antoine Taveneaux 
Tibetans are adapted to life at high altitude. Compared to more recent arrivals, notably Han Chinese, they have much lower rates of fetal growth restriction and fewer pregnancy complications (reviewed here).

For non-adapted populations, long-term residence and high altitude can lead to chronic mountain sickness, which is characterized by high levels of haemoglobin. However, the erythropoietic response to low ambient oxygen is blunted in Tibetans. Recent studies have ascribed this to a variant allele of EPAS1, the gene that encodes hypoxia-inducible factor 2alpha (HIF2a) (here).

In the current issue of Nature, Huerta-Sanchez and others confirmed that the gene had a highly unusual haplotype in Tibetans (here). It occurred rarely in Han Chinese and was entirely absent in a larger set of worldwide populations. Interestingly, however, it could be detected in the genome af an ancient hominin population, the Denisovans (see previous post). The conclusion drawn is that the EPAS1 haplotype of Tibetans derives from admixture between modern humans and Denisovans.