It is assumed that cognitive functions may be a better phenotype in genetic studies of psychiatric disorders than clinical picture itself as it is more influenced by the external factors (Gottesman, 2003). A cognitive deficit is present in ADHD patients as a matter of definition. The ADHD group differs from the non-ADHD population in terms of attention deficit and increased impulsivity. Other deficits exist in motor function inhibition. It has been found that incorrect response inhibition (which relates to impulsivity) is a suitable endophenotype of ADHD and is present as well in relatives of patients who themselves do not express clinical signs od ADHD (Slaats-Willemse, 2003, Aron, 2005). Attention is a suitable endophenotype as well (Fan, 2001). Method: In the present study the correlations between genotype and results of neuropsychological tests (TDT, TE-NA-ZO and NES2 battery) were studied in a homogenous Caucasian population of 119 boys in the age range 7-13 diagnosed with Hyperkinetic disorder (HKP - F90.x according to the ICD- 10). The genotype for “dopaminergic“ genes (DRD2, DRD4, DAT) was assessed. Results: Correlations between the results of psychological tests and genotypes of each gene were examined. The correlation coeficients for any combination were not significantly different from a random distribution. Conclusion: We did not prove any correlations between the “dopaminergic“ genes polymorphisms and the results of neuropsychological tests in our sample. Polymorphisms of these genes do not influence the performance in psychological tests in the population of Czech hyperkinetic boys.

        Key words: ADHD, hyperkinetic disorder, endophenotype, cognitive functions, genes.