Autism Spectrum Disorders: Clinical Features in a Large Portuguese Population Sample

Background: Autism spectrum disorders (ASD) are a complex, life-long neurodevelopmental disorders characterized by impaired social interaction and communication and by restricted interests and repetitive behaviours. The term high-functioning autism (HFA) is used to refer, among ASD, the individuals without Intellectual Disability (ID). The relevance of Intelligence Quotient (IQ) or Developmental Quotient (DQ) to the symptomatic expression of autism remains unclear. Macrocephaly and parents’ education level are clinical features that have been reported since Kanner’s original paper. Traditionally, family status variables such as parents' level of education have been regarded as predictors of children's academic achievement.

Objectives: Our aim was to study a large Portuguese population sample of children and adolescents diagnosed with ASD and characterize clinical features between two groups: high-functioning autism (HFA) versus autism with Intellectual Disability (ID) or global developmental delay (GDD).

Methods: Through computerized data analysis from our Autism Unit, 1188 individuals (979M/209F:4.7/1), who fulfilled the autism diagnostic criteria (all participants had ADI-R and ADOS positive results and DSM-IV-TR criteria), have been included. These sample were divided in two clinical groups, taking into account the classification of ID/GDD of the CID-9 (ID/GDD is present when the IQ/DQ<70), and matched by Full-Scale IQ/DQ score. 290 were HFA (IQ/DQ≥70). We proceeded to statistical analysis of: gender, age of diagnosis, ADIR and ADOS parameters, gestational age, neurodevelopmental profile, head circumference (measured at birth and at time of evaluation) and parents’ education level stratified. Statistical analysis (SPSS 19) was performed comparing variables between the two clinical groups. Significance level(σ)=0.05.

Results: The analyzed data showed significant statistical differences between the two groups. Exception to this was in gestational age (pMann-Whitney=0.472). Also head circumference showed similar results in both groups and above those expected from the overall population (~16% vs 3%).  At time of evaluation (N=918), 15% of HFA group and 16.8% in the group of autism with ID/GDD had macrocephaly, not observed at birth (N=843), 2.4% and 3.6%, respectively. Parent's education level had similar pattern, however was significantly higher in HFA group (χ2=37.634; p<0.001).

Conclusions: There are differences between high-functioning autism and autism with Intellectual Disability related to diagnostic and anthropometric characterization, personal history and family background. Consistent with prior evidence, macrocephaly occurred at a significantly higher frequency than in the normal reference population. It was also concluded that macrocephaly is not directly related with the severity of autistic symptoms, language or cognitive deficits. As for the parents’ education level there is an inverse relationship between it and the severity of autism. What is the implication of these findings for understanding the influence of genetic and environmental factors? In future they should be correlated with genetic analyses. These results have clinical implications, being a large sample and enhancing the importance of early diagnosis and intervention.