Introduction: several studies have reported a high frequency of epilepsy and/or co-occurrence of EEG abnormalities in children with autism spectrum disorder, although the incidence rates vary between 5% to 46%.

Methods: we analyzed two different samples of non syndromic ASD patients: an original sample encompassing 432 Italian patients and a replica sample including 714 Caucasian American patients recruited by the Autism Genetic Resource Exchange Consortium. Comparable clinical, biological and developmental variables were correlated in both samples with “presence/absence of epilepsy” or “presence/absence of EEG abnormalities”, and tested for association between each variable and biological endophenotypes by non parametric Kendall τ and Kruskal-Wallis ANOVA.

Results: in the experimental sample and in the replica sample, ASD patients positive for EEG abnormalities display a significant association with a lower risk of familial history for autoimmune/allergic diseases (Italian and AGRE sample: τ= -0.115 and -0.252, respectively; both P<0.05), and those affected by epilepsy are characterized specifically by verbal language delay in the absence of a generalized neurodevelopmental delay (Italian and AGRE sample: τ= 0.100 and 0.073; both p<0.05). Interestingly, Italian patients with EEG abnormalities show significantly lower serotonin blood levels (τ=-0.183; P<0.01).

Conclusions: these results extend previous findings, by supporting a deleterious effect of EEG abnormalities on verbal language development, and by pointing toward a protective role against the development of epilepsy for a family history of autoimmune/allergic diseases and elevated serotonin blood levels.