Attention-deficit hyperactivity disorder (ADHD) is one of the most familiar childhood psychiatric disorders. Various molecular genetic reviews indicate that genes are crucial in susceptibility to ADHD. The serotonin transporter gene (SLC6A4) has polymorphisms that correlate with ADHD. The association between ADHD and SLC6A4 gene variants in the Iranian population has not been investigated yet.

 This study analyzed the STin2 (intron 2) variant of the SLC6A4 gene in Iranian children and adolescents with ADHD.

 In this retrospective case-control study, 86 ADHD patients and 99 healthy volunteers aged five to 14 were enrolled as the case and control groups, respectively. The STin2 (intron2) fragment of the SLC6A4 gene was amplified using specific primers by conventional PCR, and three STin2 alleles of the SLC6A4 gene (STin2.9, STin2.10, and STin2.12) were examined using the acrylamide gel method.

 We found no significant difference between the ADHD and control groups in STin2.9 (34.9% vs. 39.4%, P-value = 0.824), STin2.10 (29.1% vs. 23.2%, P-value = 1.354), and STin2.12 (36% vs. 36.4%, P-value = 0.986) variants.

 There was no association between the frequency of STin2 variant alleles of the SLC6A4 gene and ADHD, but in the study of risk estimation, allele 10 of this variant was a risk allele in ADHD patients.