29526
The Association between Somatic Comorbidity and ASD Among Discordant Twins
Individuals with autism spectrum disorder (ASD) show higher prevalence of co-occurring somatic disorders than the general population, including immune dysregulation, gastrointestinal problems, and neurological problems. The co-existence of somatic problems in ASD is associated with more burden and lower quality of life. In addition, it also suggests the possibility of an underlying genetic and/or environmental perturbation affecting multiple systems that might lead to both somatic disorders and ASD. However, except some specific genetic disorders and the current findings of gene pleiotrophy, there is still little information regarding the relationships between somatic comorbidity and the symptoms of ASD.
Objectives:
This study aimed to use a monozygotic (MZ) twin sample, which has the advantage of well-controlled genetic background, to investigate if somatic comorbidity is involved in the etiological mechanism of ASD symptoms.
Methods:
Seventy-five MZ twin pairs (including 18 twin pairs discordant for ASD diagnosis and 18 typically developed (TD) twin pairs) and 60 dizygotic (DZ) twin pairs with varying autistic traits were selected for analysis in this study. A questionnaire asking past medical history and current physical problems were used to collect the information of the participants’ somatic comorbidity. All the physical problems were categorized into infectious diseases, neurological problems, gastrointestinal problems, immunological problems, and cardiovascular diseases. The Social Responsiveness Scale, Second Edition (SRS-2) was used to measure the participants’ ASD symptoms. The differences of somatic comorbidity among twins discordant for ASD and TD twins were examined. The somatic problems identified with significant within-pair differences were then tested in relation to autistic traits in both MZ and DZ twin pairs quantitatively discordant for ASD, which was defined as at least 6 points for the intra-pair difference of SRS-2 total score.
Results:
The twins with ASD in discordant MZ have more neurological problems compared to their co-twins and TD twins. However, there are no differences in infectious diseases, gastrointestinal problems, cardiovascular diseases, and immunological problems among MZ twins discordant for ASD and TD twins. For the MZ twins quantitatively discordant for ASD, the intra-pair differences of neurological problems are significantly correlated with the differences of total score of SRS-2 (r = 0.40, p= 0.001). In addition, with the conditional model for within-pair effect analysis, there is significant association between neurological problems and total score of SRS-2 (β=11.66, p= 0.002) after adjusting for ADHD and IQ.
Conclusions:
Our findings suggest that neurological problems could be considered as a non-shared environmental factor for MZ twins discordant for ASD symptoms. In addition, organic neuropathy might play a pathogenic role in the development of ASD. However, we did not find association between somatic comorbidity of other physical systems and ASD symptoms in our twin sample. Further population-based studies are warranted to validate our results.