Epigenetic analyses in Autism Spectrum Disorders: gender differences and the contribution of maternal risk factors

ASD are one of the largest groups of complex neurodevelopment disorders that affect about 1-2% of the population with a greater frequency in males, in a ratio of 4.5: 1. The diagnosis of ASD is made on the basis of the clinical observation of the subject and the use of standardized assessment scales, such as ADOS and ADI-R. In recent decades, the prevalence of this disorder has increased significantly and this is thought to be due to both a better understanding of the problem and an improvement in the process and diagnostic criteria. Although numerous studies carried out to date show a considerable variety of causes that can lead to the development of ASD, the aetiology of this disorder still remains unknown but it has been shown that environmental, genetic and epigenetic factors play an important role. In the present study we investigated, in a population of 42 girls affected by ASD, the correlation between the levels of methylation of genes associated with this disorder, maternal risk factors and symptomatological severity. To this end, the experimental protocols for the analysis of 7 genes, namely MECP2, OXTR, BDNF, 5-HTR1A, RELN, BCL-2, and EN2, were developed using the Methylation Sensitive-High Resolution Melting technique. The anamnestic data were collected through the administration of a questionnaire to the mothers on their lifestyle before and during pregnancy, while the symptomatological severity of the ASD girls were evaluated using the "gold standard" ADOS-2 psychodiagnostic tool. We also recruited 25 ASD boys as comparison population, in order to assess the presence of any differences between the two genders. The results obtained from the methylation analyses showed that, except for the MECP2 promoter, all the other investigated genes showed very low methylation levels, of about 1-2% in average. However, three of the analyzed genes, namely MECP2, OXTR and RELN, showed significant differences in mean methylation levels between males and females. The methylation levels found were subsequently correlated with maternal factors extrapolated from the questionnaire, and these correlations revealed a statistically significant association between BDNF gene methylation levels and weight gain in pregnancy. Finally, we made a correlation between maternal factors and symptomatological severity finding a statistically significant association between ASD severity and lack of folic acid intake during pregnancy. These results could suggest a role of epigenetic modifications and maternal factors in the aetiopathogenesis of ASD and therefore further studies in this sense could allow a better understanding of the importance of these factors in the pathogenesis of these disorders.