The immunogenetics of narcolepsy associated with A(H1N1)pdm09 vaccination (Pandemrix) supports a potent gene-environment interaction.

The influenza A(H1N1)pdm09 vaccination campaign from 2009 to 2010 was associated with a sudden increase in the incidence of narcolepsy in several countries. Narcolepsy with cataplexy is strongly associated with the human leukocyte antigen (HLA) class II DQB1*06:02 allele, and protective associations with the DQB1*06:03 allele have been reported. Several non-HLA gene loci are also associated, such as common variants of the T-cell receptor-α (TRA), the purinergic receptor P2RY11, cathepsin H (CTSH) and TNFSF4/OX40L/CD252. In this retrospective multicenter study, we investigated if these predisposing gene loci were also involved in vaccination-associated narcolepsy. We compared HLA- along with single-nucleotide polymorphism genotypes for non-HLA regions between 42 Pandemrix-vaccinated narcolepsy cases and 1990 population-based controls. The class II gene loci associations supported previous findings. Nominal association (P-value<0.05) with TRA as well as suggestive (P-value<0.1) associations with P2RY11 and CTSH were found. These associations suggest a very strong gene-environment interaction, in which the influenza A(H1N1)pdm09 strain or Pandemrix vaccine can act as potent environmental triggers.

Variability in the CIITA gene interacts with HLA in multiple sclerosis.

The human leukocyte antigen (HLA) is the main genetic determinant of multiple sclerosis (MS) risk. Within the HLA, the class II HLA-DRB1*15:01 allele exerts a disease-promoting effect, whereas the class I HLA-A*02 allele is protective. The CIITA gene is crucial for expression of class II HLA molecules and has previously been found to associate with several autoimmune diseases, including MS and type 1 diabetes. We here performed association analyses with CIITA in 2000 MS cases and up to 6900 controls as well as interaction analysis with HLA. We find that the previously investigated single-nucleotide polymorphism rs4774 is associated with MS risk in cases carrying the HLA-DRB1*15 allele (P=0.01, odds ratio (OR): 1.21, 95% confidence interval (CI): 1.04-1.40) or the HLA-A*02 allele (P=0.01, OR: 1.33, 95% CI: 1.07-1.64) and that these associations are independent of the adjacent confirmed MS susceptibility gene CLEC16A. We also confirm interaction between rs4774 and HLA-DRB1*15:01 such that individuals carrying the risk allele for rs4774 and HLA-DRB1*15:01 have a higher than expected risk for MS. In conclusion, our findings support previous data that variability in the CIITA gene affects MS risk, but also that the effect is modulated by MS-associated HLA haplotypes. These findings further underscore the biological importance of HLA for MS risk.