A qRT-PCR based diagnostic tool for autism spectrum disorders (ASD)

Abstract

Significant alterations in the levels of redox/methylation metabolites in autistic patients indicate a central contribution of this pathway to etiology of autism spectrum disorders (ASDs). However, the dynamic regulation of proteins and enzymes involved in these pathways at the transcriptional (mRNA) level has not yet been investigated. We hypothesized that changes in gene expression might be related to the alterations of metabolic biomarkers involved in adaptive responses to oxidative stress (decreased GSH/GSSG ratio) and decreased methylation capacity (decreased SAM/SAH ratio) observed in autistic patients. We evaluated changes in mRNA levels using qRT-PCR for blood samples obtained from autistic and non-autistic patients. Our preliminary results indicate an increased expression of several redox/methylation genes in autistic subjects, including EAAT3 (the transporter responsible for the uptake of cysteine). Cysteine is the rate limiting precursor for GSH synthesis, and GSH levels are significantly decreased in autistic subjects. In addition, mRNA levels of the folate and vitamin B12-dependent enzyme methionine synthase were increased approximately 2-fold. Methionine synthase regulates levels of methionine and homocysteine, which are reported to be decreased in autistic patients. Lastly, a significant increase in mRNA levels of the retrotransposon LINE-1 was also observed, which indicates decreased DNA methylation and epigenetic changes. These preliminary results support our hypothesis that abnormal levels of metabolites in the redox and methylation pathways are associated with altered transcriptional levels of key enzymes, as monitored in blood samples from autistic patients. These mRNA changes could potentially be useful as a clinical marker for ASD.