Exon resequencing of H3K9 methyltransferase complex genes, EHMT1, EHTM2 and WIZ, in Japanese autism subjects

Background: Histone H3 methylation at lysine 9 (H3K9) is a conserved epigenetic signal, mediating heterochromati formation by trimethylation, and transcriptional silencing by dimethylation. Defective GLP (Ehmt1) and G9a (Ehmt2 histone lysine methyltransferases, involved in mono and dimethylation of H3K9, confer autistic phenotypes an behavioral abnormalities in animal models. Moreover, EHMT1 loss of function results in Kleefstra syndrome, characterize by severe intellectual disability, developmental delays and psychiatric disorders. We examined the possible role o histone methyltransferases in the etiology of autism spectrum disorders (ASD) and suggest that rare functional variant in these genes that regulate H3K9 methylation may be associated with ASD Methods: Since G9a-GLP-Wiz forms a heteromeric methyltransferase complex, all the protein-coding regions an exon/intron boundaries of EHMT1, EHMT2 and WIZ were sequenced in Japanese ASD subjects. The detected variant were prioritized based on novelty and functionality. The expression levels of these genes were tested in blood cell and postmortem brain samples from ASD and control subjects. Expression of EHMT1 and EHMT2 isoforms wer determined by digital PCR Results: We identified six nonsynonymous variants: Three in EHMT1, two in EHMT2 and one in WIZ. Two variants, th EHMT1 ankyrin repeat domain (Lys968Arg) and EHMT2 SET domain (Thr961Ile) variants were present exclusively in cases but showed no statistically significant association with ASD. The EHMT2 transcript expression was significantly elevated i the peripheral blood cells of ASD when compared with control samples; but not for EHMT1 and WIZ. Gene expressio levels of EHMT1, EHMT2 and WIZ in Brodmann area (BA) 9, BA21, BA40 and the dorsal raphe nucleus (DoRN) region from postmortem brain samples showed no significant changes between ASD and control subjects. Nor did expressio levels of EHMT1 and EHMT2 isoforms in the prefrontal cortex differ significantly between ASD and control groups Conclusions: We identified two novel rare missense variants in the EHMT1 and EHMT2 genes of ASD patients. W surmise that these variants alone may not be sufficient to exert a significant effect on ASD pathogenesis. The elevate expression of EHMT2 in the peripheral blood cells may support the notion of a restrictive chromatin state in ASD, similar to schizophrenia.