Gene involved in dog
size identified

IN 2007 an international team identified a genetic variant that influences how big a dog can get. Dogs like the Irish wolfhound and the chihuahua dramatically illustrate the size difference among breeds.

The branch of the canine family tree that includes domestic dogs diverged from that of the gray wolf more than 15,000 years ago. Due to selective breeding by humans, dogs today have a wide range of body types and behaviors. They have the greatest diversity in body size of any mammalian species, making them ideal for studies of body size.

A research team led by investigators from NIH’s National Human Genome Research Institute (NHGRI) explored the genetic basis for size variation among dogs by comparing the DNA of various small dog breeds, including chihuahuas, toy fox terriers and pomeranians, to an array of larger dog breeds, including Irish wolfhounds, Saint Bernards and great Danes. In addition to NHGRI, their study was supported by NIH’s National Institute of General Medical Sciences (NIGMS) and other sponsors.

The study ultimately involved the analysis of DNA from more than 3000 dogs from 143 breeds. The researchers explained in the April 6, 2007, issue of the journal Science that they were able to pinpoint a specific gene sequence variant, or haplotype, associated with small size in a gene called IGF-1, which codes for a protein hormone called insulin-like growth factor 1. Nearly all of the small dogs studied shared the genetic variant, implicating it as a major influence on stature in dogs.

“The identification and characterization of a key genetic variant that accounts for differences in dog size is particularly exciting because the underlying gene is present in all dogs and other diverse species, including humans,” said Dr Eric Green, scientific director of the NHGRI Division of Intramural Research.

The finding follows on from the completion of the dog genome sequence, announced in December 2005, research that is a part of NHGRI's large-scale sequencing research network. The availability of the dog genome sequence allows researchers to better compare the human and dog genomes and narrow their search for genetic contributors to cancer and other major diseases.

“By learning how genes control body size in dogs, we are now able to learn something about how skeletal body size is genetically programmed in humans,” commented Dr Elaine A. Ostrander, the study’s senior author and chief of NHGRI’s cancer genetics branch. “We also will increase our data set of genes likely to play a role in diseases such as cancer, in which regulation of cell growth has been lost.” - NIH