Following up our earlier insights into “ancient” human deletion polymorphisms that are shared with Neanderthals or Denisovans, we published a paper in BMC Evolutionary Biology, describing a small, but neat example of likely balancing selection acting on a large, common and psoriasis-associated deletion in humans. The haplotype that harbors this deletion show unusually high variation and an excess of intermediate frequency variants. It has been common in human populations for at least 50,000 years. This deletion takes out two conserved genes, which relates to skin structure and, not surprisingly, is associated with psoriasis. All these, indicate non-neutral evolution of this variant, pointing specifically to balancing selection. Balancing selection is notoriously hard to detect and even harder to “prove” in human populations. This locus is especially interesting, since the signals that suggest balancing selection can be detected only in a very small window adjacent to the deletion. This small window would likely have been missed by genome-wide scans of balancing selection.
This paper represents one more step towards our focused-analyses of the evolution of epidermal differentiation complex, which we think is essential for understanding skin evolution and variation. Note that we published a a recent paper on filaggrin, which is a neighboring epidermal differentiation complex gene.