The latest disease to be put under the scrutiny of a large genome-wide association study is psoriasis–see articles here, here, and here. These are mostly standard studies, but once again I’m struck by the effect of the MHC (HLA) region (see the figure). It was well-known, of course, that variation in HLA affects all manner of immunity-related phenotypes, but what’s becoming clear is that this variation has much larger effects than other loci in the genome. I find this somewhat surprising–associations with MHC variability were identified because typing HLA was feasible many years ago; well before genome-wide association mapping with SNPs was even considered. This could be a case where, in the analogy to the man searching for the lost keys in the dark, looking under the lamppost was actually the best bet.
