Association Study Of DopamineD4 Receptor Gene Polymorphism And Attention Deficit Hyperactivity Disorder

Objective : To investigate the distribution of frequency of 48bp VNTR polymorphism at exon 3 of dopamine D4 receptor (DRD4) gene in Han nationality Guangxi province and the relationship between attention deficit hyperactivity disorder (ADHD) children and a 48bp repeat polymorphism in exon 3 of the dopamine receptor D4 gene .Methods:The diagnoses were ascertained according to DSM-IV criteria. DNA was extracted directly from blood lymphocytes. DRD4 48-bp VNTR allele and genotype frequencies were examined by PCR amplification. The Hardy-Weinberg equilibrium was calculated using the allele frequency.Association of polymorphisms and ADHD children were examined by comparing patients and control cases and using family-based association study in an extension of transmission disequilibrium test (TDT) and haplotype-based haplotype relative risk (HHRR).Results:Our study showed:1,In control group:the repeat numbers of 48bp VNTR polymorphism at exon 3 of dopamine D4 receptor (DRD4) gene were 2 to 7 and 4-repeat allele detected was the dominant allele of DRD4 gene at exon 3 polymorphisms with the allele frequency 0.599.Eight kinds of genotype were detected and the genotype 4*/2* was the most common genotype with genotype frequency 0.43.2,In patient group:the repeat numbers of 48bp VNTR polymorphism at exon 3 of DRD4 gene were 2 ,4 and 5 and 4-repeat allele detected was the dominant allele of DRD4 gene at exon 3 polymorphisms with the allele frequency 0.614.Four kinds of genotype were detected and the genotype 4*/2* was the most common genotype with genotype frequency 0.571.3,Genotype frequencies of ADHD children and their parents as well as the normal controls were all met the Hardy-Weinberg equilibrium.4 , The frequency distributions of allele and genotype were no significantly difference between ADHD group and control group.5,In ADHD group, the frequency distributions of allele and genotype were no significantly difference between males and females .6,No significant association was found between ADHD and 48bp VNTR polymorphism at exon 3 of dopamine D4 receptor (DRD4) by using HHRR and TDT.Conclusion:Our study showed:1,For the first time in Guangxi province that DRD4*7 alleles were found to exist among the population of the Han nationality.2,DRD4*7 alleles were not found in the Han nationality of ADHD children in Guangxi.3,The gene frequency of DRD4*4 is the most common distribution in 48bp VNTR polymorphism at exon 3 of dopamine D4 receptor (DRD4) in the the crowd of the Han nationality of China Guangxi district, which is accord with the previous reports.4,Our results did not support previous findings that there was an association between ADHD and the DRD4 gene polymerphism.The 2-repeats allele of the DRD4 gene polymorphism was unlikely a risk factor of ADHD.