Researchers have recently located mutations in dopamine receptor D4 (DRD4) exon 3 and tyrosine hydroxylase (TH) that correspond to higher levels of activity, inattention and impulsiveness in Siberian Huskies. These mutations alter the way dopamine and its precursor L-DOPA are synthesized. Dopamine functions as a neurotransmitter and is primarily involved in the reward center of the brain. Research has shown that all types of rewards generate higher levels of dopamine in the brain. Many illicit drugs work by enhancing the effects of dopamine including methamphetamine and cocaine and personality traits such as extraversion are due to greater sensitivities to rewarding behavior. Therefore alterations in it’s production can have interesting effects on behavior. Siberian Huskies were found to have seven DRD4 length variants with the shortest alleles of DRD4 and TH having the strongest correlation with ADHD. These findings correspond to earlier finding in German Shepherd dogs and also humans.
Siberian Husky was chosen for the study because of they are an ancient breed that has been interbred with wolves and are highly diverged from other dog breeds. Siberian Huskies also have have greater genetic diversity than most breeds, a trait researchers felt may help to better isolate genetic causes of behavior variability. They are also kept in more consistent environments due to their primary use as sleds dogs which researchers felt may help to better isolate “gene–behaviour relationships”.
In order to measure differences in behavior owners were asked to complete the Dog-Attention Deficit Hyperactivity Disorder Rating Scale (Dog-ADHD RS). The Dog-ADHD RS is based on the human ADHA Scale which is often given to parents to access their children. A total of 169 Siberian Huskies that were used as sled dogs were genotyped from 69 different owners. Owners were asked to provide registration information to verify that the dogs were full blood. Dogs from both North America and Europe were used in the study. After the owners had completed the Dog-ADHD RS, the Siberian Huskies were given a battery of behavioral tests by experimenters that measured their spontaneous activity when at rest and also their response to stimuli in the form of a greeting. These interaction were recorded for later analysis. After these interactions a cheek swab was collected for genetic analysis. The dogs reaction to this handling was also recorded and labeled according to manageability of the animal. The results of these experiment showed a clear correlation between the shorter variants of DRD4 and TH and increased activity, inattention, and impulsiveness.
These findings correlate with previous findings in German Shepherds and humans and show the importance of the dog as model species for studying ADHD in humans. They also give greater understanding of the role genetics plays in the behavior of the working dog and in the future, may allow better selection for desired working traits.