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

Abstract

BackgroundHistone H3 methylation at lysine 9 (H3K9) is a conserved epigenetic signal, mediating heterochromatin 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 and behavioral abnormalities in animal models. Moreover, EHMT1 loss of function results in Kleefstra syndrome, characterized by severe intellectual disability, developmental delays and psychiatric disorders. We examined the possible role of histone methyltransferases in the etiology of autism spectrum disorders (ASD) and suggest that rare functional variants in these genes that regulate H3K9 methylation may be associated with ASD.MethodsSince G9a-GLP-Wiz forms a heteromeric methyltransferase complex, all the protein-coding regions and exon/intron boundaries of EHMT1, EHMT2 and WIZ were sequenced in Japanese ASD subjects. The detected variants were prioritized based on novelty and functionality. The expression levels of these genes were tested in blood cells and postmortem brain samples from ASD and control subjects. Expression of EHMT1 and EHMT2 isoforms were determined by digital PCR.ResultsWe identified six nonsynonymous variants: three in EHMT1, two in EHMT2 and one in WIZ. Two variants, the 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 in the peripheral blood cells of ASD when compared with control samples; but not for EHMT1 and WIZ. Gene expression levels of EHMT1, EHMT2 and WIZ in Brodmann area (BA) 9, BA21, BA40 and the dorsal raphe nucleus (DoRN) regions from postmortem brain samples showed no significant changes between ASD and control subjects. Nor did expression levels of EHMT1 and EHMT2 isoforms in the prefrontal cortex differ significantly between ASD and control groups.ConclusionsWe identified two novel rare missense variants in the EHMT1 and EHMT2 genes of ASD patients. We surmise that these variants alone may not be sufficient to exert a significant effect on ASD pathogenesis. The elevated expression of EHMT2 in the peripheral blood cells may support the notion of a restrictive chromatin state in ASD, similar to schizophrenia.Electronic supplementary materialThe online version of this article (doi:10.1186/2040-2392-5-49) contains supplementary material, which is available to authorized users.

EHMT1/GLP; Biochemical Function and Association with Brain Disorders

“…Finally, exon sequencing of Japanese autism patients also identified two novel rare missense GLP and G9a variants. G9a has also been shown to be elevated in the blood of these ASD patients, suggesting an increasingly restrictive chromatin in the pathogenesis of ASD [47]. These studies link GLP to the overlapping phenotypes seen in intellectual disability disorders and autism.…”

Key role of soluble epoxide hydrolase in the neurodevelopmental disorders of offspring after maternal immune activation

“…Next, we measured expression of EPHX2 mRNA in the postmortem brain samples (BA09, BA21, BA40) from ASD patients and age-and gender-matched controls (SI Appendix, Table S5) (34). Expression of EPHX2 mRNA in the BA09 and BA40 from ASD patients was significantly higher than that of controls ( Fig.…”

Autism genetics – an overview

“…Disruption of EHMT1 by balanced chromosomal translocation was identified in two brothers with syndromic ASD . Targeted exon sequencing in a Japanese ASD cohort identified six individuals with nonsynonymous variants in EHMT1 , EHMT2 , and WIZ , which form a heteromeric methyltransferase complex . A mouse model haploinsufficient of Ehmt1 showed delayed or absent response to social novelty .…”

“…109 Targeted exon sequencing in a Japanese ASD cohort identified six individuals with nonsynonymous variants in EHMT1, EHMT2, and WIZ, which form a heteromeric methyltransferase complex. 117 A mouse model haploinsufficient of Ehmt1 showed delayed or absent response to social novelty. 118 EHMT1 controls H3K9 dimethylation, a histone modification mark that is commonly associated with gene silencing.…”