Appreciating diversity: a review of the Iranian genomic landscape

Understanding population structure is crucial for designing and interpreting human genetic studies. This is of particular importance for Iran as a large, ethnically diverse country whose population has often been treated as a genetically homogenous entity. Here, we synthesize published literature on the genetic structure of the Iranian population. We further complement this by recapitulating the geographic, historic, and ethnic background, by comparisons with neighboring countries, and by reviewing autozygosity in Iran. This synthesis confirms large genetic diversity, likely building upon an autochthonous component that was reshaped by multiple migrations. The substantial autosomal substructure falls apart into groups of largely shared genetic ancestry (Central Iranian Cluster) and those with substantial admixture in the past. Structure with respect to uniparental markers is less pronounced. We also find consistency for generally high but varying levels of autozygosity, influenced by ethnicity, residence, and socioeconomic factors. Finally, we recapitulate some examples for geographical differences in disease prevalence and (founder) mutation carrier frequency. Our synthesis emphasizes the need to account for this diversity in human genetic studies in the Iranian population. We provide conclusions for the design of such studies and state expectations on the transferability of genetic findings and genomic predictions, such as polygenic scores, within Iran as well as to neighboring countries. Iran's diversity and geographic location provide renewed motivation for conducting population genetic and ancient DNA studies as well as providing genomic reference resources in this part of the world.