Differential Gene Expression in Children with Autism Spectrum Disorder Born to Mothers with Preeclampsia
While autism spectrum disorder (ASD) is one of the most heritable neurobehavioral conditions, the heterogeneity of ASD-concordant twins supports a role for alternative mechanisms in its etiology. Maternal physiology and environmental factors can modify gene expression in-utero independent of the genes inherited and thus can influence neurogenesis and brain development. Preeclampsia is a pregnancy condition associated with poor placentation, progressive maternal inflammation and insulin resistance, and increased odds for ASD. Global gene expression profiling of children with ASD may illuminate underlying metabolic and signaling alterations that may be relevant to the pathobiology of ASD.
1) To identify genes that are differentially expressed in children with ASD born to mothers with preeclampsia, and 2) To determine how preeclampsia expression profiles differ between children with ASD and typical development (TD).
This study involved 2-5 year-old children enrolled in the CHildhood Autism Risk from Genetics and the Environment (CHARGE) population-based case-control study. Maternal preeclampsia diagnoses were abstracted from medical records. ASD diagnosis was confirmed with ADI-R and ADOS. Typically-developing controls were assessed using the Mullen Scales of Early Learning, Vineland Adaptive Behavior Scales, and Social Communications Questionnaire. RNA sequencing of peripheral blood obtained from child participants was performed on the Illumina HiSeq 2000 platform. Sequences that failed quality control or had fewer than 30 million reads were discarded, leaving 147 ASD and 70 TD samples. Reads were aligned to hg19 using Bowtie and converted to a counts table using HTSeq. To address differences in sequencing depth between samples, the counts table was normalized using binomial down-sampling. Within child diagnostic categories, we assessed whether presence of a preeclampsia diagnosis versus the absence of PE was associated with child gene expression using a negative binomial generalized linear model in the Bioconductor package edgeR with Benjamini-Hochberg FDR correction with adjustments for maternal education, child gender and ethnicity, and time from previous meal to blood draw. Gene ontological analyses were performed by the DAVID bioinformatics tool.
Hundreds of genes were differentially expressed in children exposed to preeclampsia in-utero. Ontological analyses performed on genes with a log2 fold change over 1 and under -1 indicated significant enrichment of pathways involved in nervous system development, immune function, and inflammation in children with ASD. While there was some overlap in children with TD exposed to maternal preeclampsia, interesting differences included enhancement of cell-cell signaling and oxygen binding pathways.
Fetal exposure to maternal preeclampsia is associated with differential expression of many pathways. Heightened maternal systemic inflammation has been suggested as a possible factor influencing ASD susceptibility mediated through an oxidative stress response in the fetus. These processes may be enhanced by genes involved in immunity and inflammation in children with ASD and moderated by pathways involved in oxygen binding in children with TD. Exploration of these biological pathways and potentially-alterable upstream environmental gene influences may elucidate the complex interplay between maternal gestational environment and child gene expression in ASD etiology.