Differential perinatal risk factors in children with attention-deficit/hyperactivity disorder by subtype

We compared the attention-deficit/hyperactivity disorder(ADHD) combined subtype (ADHD-C) to the ADHD inattentive subtype (ADHD-I) in terms of genetic, perinatal, and developmental risk factors as well as clinical and neuropsychological characteristics. A total of 147 children diagnosed with ADHD between the ages of 6 and 15 years participated in this study. The parents of the children completed the structured diagnostic interview, the ADHD Rating Scale-IV, the Children’s Behavior Checklist, and structured questionnaires on perinatal risk factors, and the children underwent a neuropsychological test and were genotyped. A total of 502 children without ADHD were recruited from the community as a healthy control group. The ADHD-C children showed more severe externalizing symptoms, showed more deficits in a continuous performance test, and were more likely to have comorbid disorders. Maternal stress during pregnancy, postpartum depression, and changes in the primary caretaker during first 3 years were significantly associated with both ADHD-I and ADHD-C. The ADHD-I group was less likely to have received regular prenatal check-ups and more likely to have had postnatal medical illness than the ADHD-C group. There were no significant differences in the genotype frequencies of the dopamine transporter (DAT1) and the serotonin transporter –linked polymorphic region (5-HTTLPR) polymorphisms between ADHD-I and ADHD-C groups. This study shows that the inattentive subtype of ADHD is different from the combined subtype in many parameters including severity of symptoms, comorbidity, neuropsychological characteristics, and environmental risk factors.