Differential methylation at the RELN gene promoter in temporal cortex from autistic and typically developing post-puberal subjects

Background: Reelin plays a pivotal role in neurodevelopment and in postnatal synaptic plasticity, and has been implicated in the pathogenesis of Autism Spectrum Disorder (ASD). RELN gene expression is significantly decreased in ASD, both in the brain and peripherally. Methylation at the RELN gene promoter is largely triggered at puberty and hypermethylation has been found in post-mortem brains of schizophrenic and bipolar patients. Methods: In this study, we assessed RELN gene methylation status in post-mortem temporocortical tissue samples (BA41/42 or 22) of six pairs of post-puberal individuals with ASD and typically developing subjects, matched for sex (M:F=5:1), age and post-mortem interval. Results: ASD patients display a significantly higher number of methylated CpG islands and heavier methylation in the 5’ region of the RELN gene promoter, spanning from -458 to -223 bp, whereas controls have more methylated CpG positions and greater extent of methylation at the 3’ promoter region, spanning from -222 to +1 bp. The most upstream promoter region (-458 to -364 bp) is methylated only in ASD brains, while the most downstream region (-131 to +1 bp) is methylated exclusively in control brains. Within this general framework, three different methylation patterns are discernible, each correlated with different extents of reduction in reelin gene expression among ASD individuals compared to controls. Conclusions: The methylation pattern is different in ASD and control post-mortem brains. ASD-specific CpG positions, located in the most upstream gene promoter region, may exert a functional role potentially conferring ASD risk by blunting RELN gene expression.