Dopamine DRD4 receptor polymorphism and attention deficit hyperactivity disorder

Area of Science:

• Neurogenetics
• Behavioral Genetics
• Psychiatric Genetics

Background:

• The dopamine receptor D4 (DRD4) gene is implicated in various behavioral traits and disorders.
• A specific polymorphism, a 48-bp repeat in exon 3, is known to influence gene function.
• The 7-repeat allele of DRD4 is considered a high-risk variant for several conditions.

Purpose of the Study:

• To investigate the association between the DRD4 7-repeat allele and attention deficit hyperactivity disorder (ADHD).
• To examine the relationship of this allele with ADHD-inattentive type and ADHD-combined type.
• To explore the genetic linkage of the 7-repeat allele with specific ADHD symptom dimensions.

Main Methods:

• Case-control association study comparing allele frequencies in children with ADHD and controls.
• Analysis of genetically discordant sibling pairs to assess within-family associations.
• Transmission disequilibrium tests (TDT) to evaluate linkage with ADHD symptoms.

Main Results:

• The DRD4 7-repeat allele was significantly more frequent in children with ADHD-inattentive type compared to controls.
• In sibling pairs, a higher number of 7-repeat alleles correlated with greater inattentive symptoms.
• While the 7-repeat allele was more frequent in ADHD-combined type, TDT did not find significant linkage with hyperactive-impulsive symptoms.

Conclusions:

• The DRD4 7-repeat allele shows a significant association with ADHD-inattentive type.
• Genetic evidence suggests a link between the DRD4 7-repeat allele and inattentive symptom severity.
• The association with hyperactive-impulsive symptoms was not supported by transmission disequilibrium tests.