Biomarker Insights

Introduction: The variable number of tandem repeats (VNTR) of the dopamine receptor D4 (DRD4) gene among humans may elucidate individual differences in susceptibility to neuropsychiatric diseases. Dopamine dysfunction may be involved with Attention Deficit Hyperactivity Disorder (ADHD) symptoms. In this study, we report the association between the phenotype of ADHD, a condition characterized by inattentiveness, hyperactivity, and impulsiveness, and a 48-base pair VNTR in exon 3 of the DRD4 polymorphism.

Subjects and methods: We used a case control approach conducted on 29 ADHD and 31 ethnically matched control Egyptian children (ages 6–12 years). Cases were assessed by a psychiatric semi-structured interview and the Conners' Parent Rating Scale. VNTR polymorphisms of the DRD4 gene were done by touchdown PCR program using exon 3-specific primers followed by agarose gel electrophoresis.

Results: We observed a significant association between the existence of D4.4 allele of DRD4 and ADHD (P < 0.002); 6.9% of cases showed a single D4.4 and 10.3% showed a double D4.4 as compared to controls in whom D4.4 has never been detected.

Conclusion: Children with smaller number of repeat alleles (two to four repeats) of the DRD4 gene have higher possibility to develop ADHD in Egyptian children.