Genome, epigenome and RNA sequences of monozygotic twins discordant for multiple sclerosis

Identical (or more correctly 'monozygotic') twins are widely used to study the contributions of genetics and environment to human disease. A study that focused on three pairs of monozygotic twins, in which one twin had multiple sclerosis and the other did not, has brought the latest techniques of genome sequencing and analysis to this field, and incidentally published the first female human genome sequences. Full sequences were determined for one pair of twins, and for these and the other two pairs the mRNA transcriptome and epigenome sequences of CD4+ lymphocytes were determined. The striking result is that no genetic, epigenetic or transcriptome differences were found that explained why one twin had the disease and the other did not. Digging deeper into the data, eQTL (expression quantitative trait locus) mapping revealed tantalizing differences within twin pairs that merit closer examination. And some possible causes can be ruled out. Future work might usefully concentrate on studies of other cell types and epigenetic modifications.