A recent study has identified a link between polymorphism of the dopamine D4 receptor gene (DRD4) in German shepherd police dogs and increased hyperactivity and impulsivity. Polymorphism of DRD4 at exon 3 has been linked to ADHD in humans and, although the gene has also been identified in horses, chimpanzees and dogs, this is the first study to investigate the association between canine behaviour traits and DRD4 alleles.
In this study two alleles, known as 2 and 3a, of DRD4 were identified, each containing 315 and 327 nucleotide base pairs respectively. Each of the 241 pet and police German shepherds investigated had their activity-impulsivity and inattention evaluated using a recently validated dog-ADHD Rating Scale. It was found that in police dogs which exhibited heterozygous alleles or homozygous 3a alleles, the activity-impulsivity rating was significantly higher than those individuals whom were homozygous 2. There was no significant difference detected between the pet German shepherds, regardless of the presence of 3a alleles.
The difference in the phenotypic expression of the 3a allele in police dogs and pet dogs may be linked to gene-environment interactions. Police German shepherds could be considered ‘environmentally homogenous’ – they are all exposed to the same training, environment and experiences. As this is the case, expression of the allele is easier to identify as it is not masked by environmental elements. Alternatively there are discrepancies between the training and life experiences of pet German shepherds, and these inconsistencies may conceal the effect of DRD4 polymorphism in the phenotypic behaviour.
Reference List
Primary Reference
Hejjas, K., Vas, J., Topal, J., Szantai, E., Ronai, Z., Szekely, A., Kubinyi, E., Horvath, Z., Sasvari-Szekely, M., Miklosi, A., 2007. Association of polymorphisms in the dopamine D4 receptor gene and the activity-impulsivity endophenotype in dogs. Animal Genetics 38, 629-633.
Abstract found online at: http://www.ncbi.nlm.nih.gov/pubmed/17986156
Secondary Reference
Vas, J., Topal, J., Pech, E., Miklosi, A., 2007. Measuring attention deficit and activity in dogs: A new application and validation of a human ADHD questionnaire. Applied Animal Behaviour Science 103, 105-117.
Abstract found online at: http://linkinghub.elsevier.com/retrieve/pii/S0168159106000955
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