Objective: To investigate the relationship between two HTR1D gene polymorphisms, 1350T>C and 1236A>G polymorphisms, and attention deficit hyperactivity disorder (ADHD) comorbid or not comorbid learning disorder (LD).
Methods: Blood samples were taken from 91 trios with probands of ADHD comorbid LD and 181 trios with probands of ADHD not comorbid LD. DNA was extracted. 1350T>C and 1236A>G were genotyped by restriction fragment length polymorphism analysis. Transmit/disequilibrium test and haplotype analysis were used to test the association between the two polymorphisms of HTR1D gene and ADHD comorbid or not comorbid LD separately.
Results: 1236A allele (chi2=5.306, P=0.021) was over transmitted to probands of ADHD without LD. No biased transmissions of any allele and haplotype were found in families with probands of ADHD with LD.
Conclusion: whether ADHD comorbid LD or not comorbid LD makes difference at the level of HTR1D gene polymorphism of 1236A>G.