Genomics and epigenomics in rheumatic diseases: what do they provide in terms of diagnosis and disease management?

Epigenome-wide cross-tissue correlation of human bone and blood DNA methylation - can blood be used as a surrogate for bone?

Difficulty in obtaining bone tissue is an obstacle to studying epigenetics to understand gene–environment interactions, and their role in disease pathogenesis. Blood is an obvious alternative and in this proof of principle study, our aim was to systematically investigate whether blood is a viable surrogate for bone. We measured epigenome-wide DNA methylation at 850 K CpG sites in matched trabecular bone and peripheral blood collected from the same patients at the same time-point (n = 12 women; 66–85y), to investigate the between-tissue correspondence. What constituted a CpG site with corresponding methylation in both tissues was stringently defined. Only sites highly correlated (r² > 0.74; FDR q-value <0.05) and at least 80% similarity in methylation level (Δβ <0.2) between paired samples were retained. In total, 28,549 CpG sites were similarly methylated in bone and blood. Between 33% and 49% of loci associated with bone phenotypes through GWAS were represented among these sites, and major pathways relevant to bone regulation were enriched. The results from this study indicate that blood can mirror the bone methylome and capture sites related to bone regulation. This study shows that in principal, peripheral blood is a feasible surrogate for bone tissue in DNA methylation investigations. As the first step, this will provide a platform for future studies in bone epigenetics, and possibly for larger-scale epidemiological studies.

Sex and autoimmune disease: Four mechanisms pointing at women

The ultimate goal of modern medicine is a personalized approach being tailored on the single patient, ie, tailored, based on a finely tuned definition of the immunogenetics, epigenetics, microbiome, and biomarkers, to maximize results and minimize risks particularly of new targeted treatments. Among individual factors around which to tailor the patient management are sex and age, with gender-medicine finally becoming central to the research agenda. Of note, we are not convinced that a whole personalized medicine approach in its current form will necessarily include gender medicine and thus this should remain central to the research agenda. To tackle this crucial issue, however, we should first be able to answer a question of paramount importance, that is, why does autoimmunity affect women more than men? The growing number of experimental works in this area militate against an easy answer to this question, but we will herein briefly discuss four major candidates (sex hormones, sex chromosomes, environmental factors, and the microbiome) to which some unsuspected others may be ancillary.