The association of disease severity, repetitive behaviours, social withdrawal, and gastrointestinal system symptoms with heart rate variability, cholecystokinin, and oxytocin level in autism spectrum disorder: A case-control study

Objective: This study aimed to examine the relationship of autonomic function and possible autonomic dysregulation with the clinical presentation of autism spectrum disorder (ASD) in children with ASD. For this purpose, resting heart rate variability (HRV) reflecting autonomic function and neuropeptide hormones closely related to the autonomic nervous system, oxytocin (OXT) and cholecystokinin (CCK), were explored in children diagnosed with ASD to discover their relations to autism severity, social dysfunction, repetitive behaviours, and gastrointestinal system (GIS) symptoms seen in autism. Method: The sample of the study was included 29 children (1 girl, 28 boys) without any acute or chronic medical illness, who aged 3-8 years, diagnosed with autism spectrum disorder according to DSM-5 diagnostic criteria and who applied to Karadeniz Technical University Faculty of Medicine Child and Adolescent Psychiatry outpatient clinic between the dates of September 2020 and February 2021 and it consisted of 31 healthy children (2 girls, 29 boys) aged 3-8 years who applied to Karadeniz Technical University Faculty of Medicine Child and Adolescent Psychiatry or General Pediatrics outpatient clinic between the exact dates. The Sociodemographic and Clinical Data Form, Childhood Autism Rating Scale (CARS), Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children - Present and Lifetime Version – Turkish Adaptation (K-SADS-PL-T) and the 6-Item Gastrointestinal Severity Scale (6-GSI) were filled in by obtaining information from the parents and with clinical evaluation by the clinician, and the parents completed the Aberrant Behaviour Checklist (ABC). A 10-minute baseline heart rate variability measurement was then made. After the measurement, 5 cc of blood was taken from the patient to the biochemistry tube for the serum levels of oxytocin and cholecystokinin, and it was transferred to the Medical Biochemistry Department Laboratory to be stored at -80°C until analyzed. The obtained data were analyzed using IBM SPSS 22. Results: Of all participants, 91.1% (n= 57) were boys, and the mean age was 64.68 ± 19.62 months. There was no significant difference between the case and control groups in terms of gender and age. 79.3% of children with ASD had psychiatric comorbidity. Enuresis nocturna was detected in only two children in the control group. This study found no significant difference between the ASD group and healthy controls regarding baseline heart rate variability values. However, serum OXT levels were significantly lower in children with ASD compared to healthy controls (p< .001). In contrast, serum CCK levels were significantly higher than the control group (p< .001). There was no correlation between the severity of repetitive behaviours and baseline HRV values, serum OXT, and CCK levels in the ASD group. On the other hand, the LF/HF ratio reflecting sympathetic dominance was positively correlated with the CARS total scores (r= .502 p= .006), while HF value indicating parasympathetic dominance was found to be negatively correlated (r= -.379 p= .043). A marginal positive correlation (r= .365 p= .052) was found between LF/HF ratio and ABC social withdrawal subscale scores. In addition; OXT levels were positively correlated with CARS total (r= .383 p= .040), ABC social withdrawal subscale (r= .477 p= .009), and GSI bloating scores (r= .438 p= .017). While no correlation was observed between CCK levels and CARS total scores (p= .200), CCK and ABC social withdrawal scores (r= .417 p= .024) showed a positive correlation. In addition, CCK levels were negatively correlated with GSI diarrhea scores (r= -.390 p= .036). No correlation was found between HRV values, serum OXT and CCK levels, which were examined as indicators of autonomic function in this study. However, a positive correlation was found between the LF value of HRV, which reflects sympathetic dominance, and CCK levels after controlling for the presence of comorbidity (r= .404 p= .033). Conclusion: In conclusion, while there was no difference between the ASD group and the control group regarding HRV values, which we used as indicators of autonomic function in this study, serum OXT levels were found to be lower and serum CCK levels higher in the ASD group compared to the control group. It was shown that as the severity of the disease and deterioration in social withdrawal symptoms increased, the HRV value reflecting sympathetic dominance increased. At the same time, the OXT level also paradoxically increased in the group with ASD. There was no relationship between ASD disease severity and CCK levels; however, as the level of CCK increased, the impairment in social withdrawal symptoms, which is the core symptom of ASD, has also increased. In this study, there was no relationship between HRV values, OXT, and CCK levels, which can be considered autonomic system markers; however, when controlled the presence of comorbidity, a positive correlation was found between the sympathetic dominance value of HRV and CCK. In addition, it was observed that there was no relation between GIS symptoms related to the enteric system as a part of the autonomic system and HRV values, and it is thought that further studies with larger samples are needed to support the results obtained about OXT and CCK levels. In conclusion, this study supports the autonomic dysfunction hypothesis in children with ASD and is the first study to show the relationship between ASD symptomatology and CCK levels. However, there is a need for new studies investigating CCK levels in the diagnostic groups accompanying our patients and the potential role of CCK in the treatment of ASD. Keywords: autism spectrum disorder, autonomic dysregulation, heart rate variability, oxytocin, cholecystokinin