Genetic polymorphisms of the neurotransmission systems are intensively studied in the human because of a possible influence on personality traits and the risk of psychiatric disorders. The investigation of genetic variations of the dog genome has recently been a promising approach, as a considerable similarity can be observed between dogs and humans, in both genetic and social aspects, suggesting that the dog could become an appropriate animal model of human behavioral genetic studies. The aim of our study was the identification and analysis of variable number of tandem repeats polymorphisms (VNTRs) in the genes of the dopaminergic neurotransmitter system of dogs. The in silico search was followed by the development of PCR-based techniques for the analysis of the putative VNTRs. Highly variable repetitive sequence regions were found in the tyrosine hydroxylase (TH), dopamine transporter (DAT), and dopamine β-hydroxylase (DBH) genes. Allele frequency and genotype distribution of these novel polymorphisms together with the exon 3 and exon 1 VNTR of the dopamine D4 receptor gene were determined in a large sample involving four dog breeds (German Shepherd, Belgian Tervueren, Groenandael, and Malinois) and European Grey Wolves. A significant difference of allele and genotype frequencies was demonstrated among the analyzed breeds; therefore, an association analysis was also carried out between the activity-impulsivity phenotype and the described VNTRs. Preliminary findings are presented that polymorphisms of the DRD4, DBH, and DAT genes can be associated with attention deficit among Belgian Tervuerens.
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