Different polymorphisms of the oxytocinergic system explain the prevalence of autistic traits in different populations and the influence of oxytocin on the HPA
Several recent studies demonstrated that different single nucleotide polymorphisms of the oxytocin receptor gene are associated with impairments of social behavior including the heritability of autism. Another focus of attention has been the CD38 protein, which stimulates the release of oxytocin in the blood stream and probably in the brain. The objective of this study was to investigate if the prevalence and severity of autistic traits in a healthy sample of academic students is influenced by three different SNPs of OXR rs53576 and CD38 rs3796863, and in a second experiment their action in the HPA axis in a social challenge. For the first purpose, 333 subjects, 205 men and 128 women, answered the self-report questionnaires on autistic traits (The Adult Autism Quotient (AQ), Empathy Quotient (EQ), and Systemizing Quotient (SQ)) and were genotyped by cheek swab. For the second, 80 male participants were additionally submitted to the Trier Social Stress Test. Comparisons between men and women confirm reported findings that women have higher scores on the EQ and lower scores on SQ, with no differences on AQ. However, it was observed that women have less autistic traits on the communication subscale (AQ). In our study a gender-SNP, and in the female sample, a SNP-SNP interaction in prevalence of autistic traits were for the first time observerd. In the female sample, the presence of at least one protective allele (A) on CD38 rs3796863 was associated with a higher score on the EQ and the analysis of the interaction suggested that this effect is partially modulated by the presence of the critical allele (A) on the OXTR rs2254298. In the male, the exclusive effect of OXTR rs53576 on the prevalence of autistic traits and the existence of a dose dependent effect of the critical allele (A), was identified. Our study also confirms the role of oxytocin on the modulation of HPA stress reactivity since higher salivary cortisol levels just before the stress situation and at the endpoint were observed in OXTR rs225429A+. Additionally, this group also showed a higher increase in cortisol concentration during the stress-phase. These results help to explain the difference prevalence of autistic traits and empathy among men and women, since the prevalence of the alleles are different and their effects, gender-specific. Future studies should also include this and other variables, like ethnicity, which is also associated with different allelic distribution.
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