Trans-effects of chromosome aneuploidies on DNA methylation patterns: DNA methylation analysis of Down syndrome in human brain tissues and cells. Homo sapiens

Background: Trisomy 21 causes Down syndrome (DS), but the mechanisms by which the extra chromosome leads to deficient intellectual and immune function are not well understood. Results: Here, we profile CpG methylation in DS and control cerebral and cerebellar cortex of adults and cerebrum of fetuses. We purify neuronal and non-neuronal nuclei and T-lymphocytes and find biologically relevant genes with DS-specific methylation (DS-DM) in brain cells. Some genes show brain-specific DS-DM, while others show stronger DS-DM in T cells. Both 5-methyl-cytosine and 5-hydroxy-methyl-cytosine contribute to the DS-DM. Thirty percent of genes with DS-DM in adult brain cells also show DS-DM in fetal brains, indicating early onset of these epigenetic changes, and we find early maturation of methylation patterns in DS brain and lymphocytes. Some, but not all, of the DS-DM genes show differential expression. DS-DM preferentially affected CpGs in or near specific transcription factor binding sites, implicating a mechanism involving altered transcription factor binding. Methyl-seq of brain DNA from mouse models with sub-chromosomal duplications mimicking DS reveals partial but significant overlaps with human DS-DM and shows that multiple chromosome 21 genes contribute to the downstream epigenetic effects. Conclusions: These data point to novel biological mechanisms in DS and have general implications for trans effects of chromosomal duplications and aneuploidies on epigenetic patterning. Overall design: Bisulfite converted DNA from 119 samples from Down syndrome patients and controls were hybridised to the Illumina Infinium 450k Human Methylation Beadchip. In addition, we re-analyzed 6 Down syndrome and 6 control cerebellum DNA samples on the 450K BeadChips using an adaptation of the Illumina probe preparation protocol (TrueMethyl kit; Cambridge Epigenetics, CEGX), in which parallel analyses of bisulfite and oxidative bisulfite DNA for each sample allows assessment of the relative contributions of 5mC and 5hmC to net methylation.