Nature Genetics this week has published a genome-wide association study of narcolepsy in the Japanese population. The finding in the paper is a variant that confers a modest risk of narcolepsy, but personally, I was blown away by Figure 1, reproduced above. The figure shows the strength of association of each of 500,000 SNPs with narcolespy, and the novel reproducible finding is on chromosome 22 (ie, it doesn’t stand out all that impressively in this plot). The major signal, absolutely swamping everything else, is in fact in the MHC region (called HLA in humans).
This region, of course, contains risk factors for type I diabetes, crohn’s disease, and most (all?) other autoimmune diseases. A quick google confirms that, indeed, thinking of narcolepsy as an autoimmune disease is not new, but it’s definitely new to me, and it’s pretty striking to see just how much more important the risk factors in HLA are compared to everything else.