Saturday, May 7, 2016

Fat mutant labradors FAQ

The study about a mutation associated with obesity in labrador retrievers has received massive news coverage for a dog genetics article (and you can see how happy the researchers are about it at @GODogsProject). So what does it mean for your dog?

Image: Raffan et al., 2016

  • Do all labs have this mutation? No. They tested 383 UK labs and found that of 383 Labrador retrievers from the UK, 78% of them didn't have this mutation at all; 20% had one copy of the mutation (were heterozygous); and 2% had two copies (the maximum number you can have; they were homozygous). They tested some US labs as well and found similar frequencies.
  • Do any other breeds have this mutation? Yes, it was also found in flat-coated retrievers, a breed closely related to the lab. The researchers tested 38 other breeds, testing 8-55 dogs per breed. (The list of breeds they tested is provided.) They tested 55 golden retrievers, another closely related breed to the lab, without finding this mutation. That doesn’t mean it’s not out there, but it does suggest that if it is present in other breeds, it’s much less common in them than in labs.
  • If my dog has this mutation, does it mean my dog is doomed to be fat? No. They did show an association between the mutation and weight: dogs who have one copy of the mutation are, on average, 1.90 kg (4.18 lbs) heavier than dogs who have no copies. Dogs who have two copies are on average 3.8 kg heavier than dogs who have no copies. (This is in labs, but the numbers in flatties are very similar.) But that’s an average. It’s not all about genetics. Some dogs who have this mutation won’t put on that much extra weight, and some dogs who have it will put on more. The gene they studied will interact with other genes to affect your dog’s eating habits and metabolism, and of course in weight gain as in behavior, the environment (food type, food amount, exercise) is a huge factor.
  • If my dog is fat, does it mean my dog probably has this mutation? Not necessarily. There are lots of reasons to get fat.
  • Is this “the gene” for weight gain? In dogs as in humans, multiple genes control weight. This is just one, albeit one with a pretty impressive effect in this breed. And again, remember the importance of environmental factors!
  • How does this mutation cause weight gain? It may have to do with causing dogs to want to eat more (certainly a trait we’ve all seen in labs!). It may also change their metabolism directly, affecting how they turn calories into energy.
  • Where did the mutation come from? Both labs and flat-coats are descended from the St. John’s water dog, a breed which is no longer around. The researchers have reason to believe that the mutation dates back to that breed.
  • Does this mutation make labs easier to train? Possibly. The researchers tested a population of labs who are used as breeding stock for assistance dogs, and found that many more of them carried the mutation than in the general population: 23% had zero copies, 64% had one copy, and 12% had two copies. Additional genetic analysis suggested that these dogs are being actively selected for this mutation (unbeknownst to the people who are selecting them!). This suggests that something about this mutation makes dogs better at assistance work — perhaps making them more food motivated and easier to train.
  • Does this mutation make flat-coats fat, too? It does, and yet flatties aren’t known for obesity the way labs are. It’s a bit of a head scratcher.
  • What's the big deal? Didn’t we already know that labs are food-obsessed mutants? I know, right?
Raffan, Eleanor, et al. "A Deletion in the Canine POMC Gene Is Associated with Weight and Appetite in Obesity-Prone Labrador Retriever Dogs." Cell Metabolism (2016). It’s open access and, as modern genetics papers go, not that hard a read. Check it out!

Want to know more about dogs and genetics? I have a class on it starting Monday, May 9! We will learn concepts like homozygosity and heterozygosity, and I will be happy to discuss this study in more depth.


  1. Great Article, although the numbers are a bit off. There were 310 Labs in the study. The researchers believe that the predisposition towards obesity is due to the relationship the gene in question(POMC) plays within the melanocortin system, which in humans has been shown to lead to increased appetite and obesity.

    The researchers also address the issue of FCR's not being thought of as prone to weight gain, The breed's rarity.

    I would love to discuss it further with you in your upcoming class, but alas, I can't afford it at the moment.

    1. 310 labs were used to find the initial association between genotype and phenotype, but 383 were used to find the prevalence of the genotype.

      I do hope to find time in the next few days to blog the "geek version" of the study in which I'd go in to POMC and the specific changes that were found, which were really interesting.

      Sorry to hear you can't afford the class! I have been pondering for a while now what sort of approach might be affordable for students while still providing income for myself and supporting IAABC (an organization that definitely deserves supporting). It's a tough question!

    2. Oh I'm so looking forward to the geek version! I am an amateur science nerd :) Is there a misprint in the article? I thought I read they initially ran the sequences of 18(I believe) Labs to check for correlations of the 4 candidate genes and obesity/adiposity/appetite. Then once they found the 14bp deletion mutation in the POMC gene they tested the 310 other labs?

      Regardless, I can't tell you how excited I am to find a blog dedicated to the "science of dogs". My science nerd + my love of my dogs makes this nirvana on the interwebz!

    3. It's not a misprint, they just used different groups for different parts of the study -- go to the paper and just do a text search for "385" and you'll find the bit where they used that population (to determine prevalence, which was what I was writing about in that particular point).

      There are LOTS of dog science bloggers around! Check out Dog Spies, Companion Animal Psych, Do You Believe in Dog, The Science Dog... I'm sure I'm missing some (sorry to those I missed).

  2. I have a fat mutant lab with short, stumpy legs. She's exceedingly sweet and easy to teach. Also, her belly looks like a potbellied pig's.