[Transmission disequilibrium test of DRD4 exon III 48bp variant number tandem repeat polymorphism and tic disorder].

Objective: To investigate whether DRD4 exon III48 bp variant number tandem repeat(VNTR) polymorphism is associated with tic disorder.
Methods: One hundred and twenty-two nucleus families were collected using Structured clinical interview for genetic study of Tourette syndrome and related disorders for family-based association analysis of tic disorder and DRD4 exon III 48bp VNTR polymorphism. One hundred and twenty-two trios were divided into two groups: tic disorder group (82 trios of Tourette syndrome or chronic tic disorder, TS&CT) and tic disorder accompanied with attention deficit and hyperactivity disorder (ADHD) group (40 trios of Tourette syndrome or chronic tic disorder accompanied with ADHD, TS&ADHD). Transmission disequilibrium test (TDT), in addition to polymerase chain reaction and VNTR technique were conducted in 122 trios.
Results: There exist 5 alleles at this polymorphic locus in this sample including DRD4 exon III 48bp 2-6 repeats. No transmission disequilibrium was found between DRD4 exon III 48 bp VNTR and tic disorder (chi square=7.44, P 0.12); however, when the sample was divided into two groups, transmission disequilibrium was noticed between the cases of TS&ADHD and this locus by overall allele-wise analysis (chi square=11.74, P 0.02), and there exists transmission disequilibrium exclusively between 5 or 6 repeats of 48bp VNTR(longer alleles) by allele-wise analysis (chi square=10.57, P 0.032, chi square=6.13, P 0.01). No transmission disequilibrium was seen between TS&CT and DRD4 exon III 48bp VNTR(chi square=3.38, P 0.50).
Conclusion: The results of this study have revealed an association between the longer alleles of DRD4 exon III 48bp VNTR polymorphism and tic disorder accompanied with ADHD, thus suggesting a possible genetic risk factor of tic disorder accompanied with ADHD in Chinese.