Pro-opiomelanocortin (POMC) Gene Mutation
What is POMC gene mutation?
In 2016, researchers identified a gene, called the pro-opiomelanocortin (POMC) gene, that contributes to obesity in Labrador Retrievers. A specific mutation of this gene, involving the deletion of 14 DNA base pairs, has been shown to contribute to increased body weight, increased body fat percentages, and increased food motivation in Labrador Retrievers.
At this time, the POMC gene mutation has only been shown to play a role in Labrador Retrievers and the closely-related Flat Coated Retriever. Studies in nearly forty other dog breeds have failed to demonstrate the presence of this mutation in any other breed. Humans can possess a similar mutation however, and therefore Labrador Retrievers are currently being used as a model for human obesity in some studies.
How was the POMC gene mutation discovered?
Labrador Retrievers have a demonstrated incidence of obesity that is higher than any other breed, as well as higher levels of food motivation than other dog breeds. Therefore, researchers elected to use Labrador Retrievers in a large-scale study aiming to examine the genetic causes of obesity in dogs.
“Researchers discovered that a specific mutation of the POMC gene was associated with increased body weight, increased body fat, and increased food motivation.”
Three hundred Labrador Retrievers, including pets and assistance dogs, were evaluated based on weight, body fat, and food motivation. Researchers examined three genes in these dogs, each of which was thought to potentially influence obesity. Two of the studied genes were found not to affect obesity, but researchers discovered that a specific mutation of the POMC gene was associated with increased body weight, increased body fat, and increased food motivation. This suggests that the POMC gene mutation is an important contributor to obesity in Labrador Retrievers.
What are the clinical signs of POMC gene mutation?
Approximately 25% of Labrador Retrievers carry the POMC gene mutation, according to the results of the 2016 study. Affected dogs typically have a higher body weight and higher body fat composition than unaffected dogs, and also show increased appetite and food motivation.
“While the general occurrence of the POMC mutation in Labrador Retrievers is approximately 25%, it was found that 76% of the service dogs test carried this genetic mutation.”
Interestingly, the increased food motivation seen in dogs with the POMC gene mutation often means that these dogs are easier to train. Researchers observed that service dogs are significantly more likely to carry the POMC mutation than non-service Labrador Retrievers. While the general occurrence of the POMC mutation in Labrador Retrievers is approximately 25%, it was found that 76% of the service dogs test carried this genetic mutation. These dogs are ideal candidates for training because they are highly treat-motivated, even though their resulting obesity may impact their ability to perform their work effectively later in life.
How does the POMC gene mutation contribute to obesity?
The POMC gene codes for two proteins, beta-MSH (melanocyte-stimulating hormone) and beta-endorphin. These proteins are thought to play a role in satiety (signaling the brain to end the sensation of hunger once a dog eats a meal). In a dog with the POMC gene mutation, it is theorized that the brain does not receive these signals as effectively, and therefore the dog remains hungry even after an adequate meal.
How is POMC gene mutation diagnosed?
In 2017, the University of Cambridge in the UK will begin offering a genetic test for the POMC gene. This test is only recommended for Labradors and Flat-Coated Retrievers, as POMC gene mutations have not been detected in other breeds.
How is POMC gene mutation treated?
“Owners of dogs with a known or suspected POMC gene mutation should work with their veterinarian to develop a program of diet and exercise that will allow their dogs to maintain a healthy weight.”
At this time, there is no specific treatment available for the POMC gene mutation. It is important to note that the POMC gene mutation increases appetite, but these effects can be overcome with careful regulation of calorie intake and exercise. Owners of dogs with a known or suspected POMC gene mutation should work with their veterinarian to develop a program of diet and exercise that will allow their dogs to maintain a healthy weight.
Medications are currently under development in human medication to treat POMC deficiency. At this time, it is too early to say whether these medications may have applications in veterinary patients.
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