Association Between Methylation Status Of CpG Island In DAT1 And DRD4 Genes And ADHD, And Its Clinical Symptoms

Objectives:To explore the difference of methylation status of CpG island in DAT1 and DRD4 genes promoter region between Attention Deficit Hyperactivity Disorder (ADHD) children and normal children, and to investigate the correlation of methylation status in DAT1 and DRD4 genes and severity of clinical manifestations in ADHD patients. Based on the above results, we could further understand pathogenesis of ADHD from a epigenetics point of view, and the relationship between central nervous dopamine system and clinical symptoms of ADHD.Methods:111 ADHD patients and 118 normal controls were enrolled in the present study. We collected the demographic data and peripheral venous blood from both ADHD patients and normal controls. Clinical symptoms and cognitive functions were also assessed for ADHD patients. Bisulfite genomic sequencing (BGS) was used to define the methylation status of every CpG site in DAT1, DRD4 gene promoter CpG island.Results:1.No significant differences were found between ADHD patients and normal controls on percentage of methylated CpG site in total CpG island for both DAT1 and DRD4 genes(p>0.05). However, the percentage of methylation in No.17 CpG site for DAT1 and No.8 CpG site for DRD4 were higher in ADHD patients compared to normal controls(p<0.05).2. In all samples, percentage of methylated CpG site in total CpG island for DAT1 gene was higher in males compared to females(p<0.05), whereas that for DRD4 gene was higher in females compared to males (p<0.05); the similar gender differences on methylation level for DAT1 gene was found in ADHD patients and for DRD4 gene in normal controls(p<0.05).3. In all samples and in ADHD patients, percentage of methylated CpG site in total CpG island for DAT1 gene was higher in individuals over 7 years old compared to individuals at 1-7 years old(p<0.05). In ADHD patients, percentage of methylated CpG site in total CpG island for DAT1 gene was higher in individuals whose course was over 4 years compared to individuals whose course was between 1-4 years (p<0.05).4. In ADHD patients, percentage of methylated CpG site in total CpG island for DAT1 gene was higher in individuals without depression, anxiety or ADHD family history when compared with individuals with above family history (p<0.05).5. In ADHD patients, percentage of methylated CpG site in total CpG island for DAT1 gene was higher in individuals whose ODD(Oppositional Defiant Disorder) score were below 9 compared to individuals whose ODD score were≥9 (p<0.05). However, no statistical differences on methylation level for DAT1 genes were found between high and low ADHD-RS-IV total score (≤30 vs.>30), ADHD-RS-Ⅳ inattention score(≤17 vs.> 17), and ADHD-RS-IV hyperactivity/impulsivity score (≤13 vs.> 13) subgroups (all p<0.05).Conclusions:1. Methylation status of CpG island in DAT1 and DRD4 genes promoter region might correlate with ADHD susceptibility.2. Methylation status of CpG island in DAT1 and DRD4 genes show differences in different age and sex.3. Methylation status of CpG island in DAT1 gene might influence the severity of oppositional defiant symptom in ADHD patients.