Discrepancies in the role of the 40 bp VNTR polymorphism of the dopamine transporter gene (DAT1) in attention-deficit hyperactivity disorder (ADHD) could be due to various sources of genetic or phenotypical heterogeneity. We therefore analyzed a sample of 146 ADHD children and their parents, with a transmission disequilibrium test (TDT) design, assessing age, inattention, and hyperactivity dimensions and total score of the ADHD Rating Scale, the number of errors and the total score at Stroop Color-Word test, and the total score at the Trail Making Test. The TDT for 10-repeat (10-R) allele shows a perfect lack of transmission bias (Mc Nemar chi(2) = 0) and PBAT analyses showed no role of this polymorphism for any of the studied endophenotypes. Lack of statistical power is always a possibility, but with a sample size above the average of the majority of previous studies, and an odds ratio (number of transmitted versus untransmitted 10-R allele) of 1.00 exactly, this possibility may be considered as not very likely.
Copyright 2008 Wiley-Liss, Inc.