Autism and Schizophrenia: The Antithesis of Each Other?
24 November 2014: Genomic imprinting is a phenomenon where one parental allele is silenced epigenetically, resulting in monoallelic parent-of-origin gene expression (Jirtle and Weidman 2007). It evolved about 150 million years ago with the advent of viviparity and placentation in a common ancestor to Therian mammals (i.e. Marsupials and Eutherians) (Killian et al. 2000). Badcock and Crespi postulated in their imprinted brain theory that autism spectrum disorders (AS) and schizophrenia spectrum (SS) disorders are the antithesis of each other, and result from the skewing of paternally and maternally imprinted gene expression in the brain during development. Paternally expressed imprinted genes tend to be progrowth, and those that are maternally expressed antigrowth. This theory predicts that full term above average-sized babies would have a significantly higher risk of AS disorders concomitant with a significantly lower risk of SS disorders. In contrast, full term below average-sized babies would have a lower risk of AS, but a significantly greater risk for developing SS disorders. This unique opposite risk pattern for AS and SS disorders was indeed demonstrated to be associated with normal variation in birth size in a recent Danish study (Byars et al.) of 1.8 million babies of which 95 thousand had AS or SS. Now, to assess the role that imprinted gene dysregulation plays in the genesis of these neurological disorders, we need to identify the complete repertoire of human imprinted genes, and their regulatory elements, the imprintome (Skaar et al. ).