Why do these rabbits do handstands and walk on their front paws instead of hopping?

Sauteur d'Alfort, a breed of domesticated rabbits, do "handstands" and walk on their front paws instead of hopping. New research suggest the strange behavior is likely caused by a mutation in a gene linked to limb movement. Understanding the mutation could help scientists better understand movement and the workings of the spinal cord in many other animals, including humans. From Science News:

In the rabbit study, [Uppsala University molecular geneticist Leif] Andersson and colleagues bred hop-less sauteur d'Alfort male rabbits with New Zealand white female rabbits that can hop. The team then scanned the genetic blueprints of the offspring that couldn't hop and looked for mutations that didn't appear in offspring that could.

A mutation in the RORB gene popped up as a likely candidate for the rabbits' acrobatic handstands. That change creates faulty versions of the genetic instructions that cells use to make proteins, the researchers found. As a result, there appears to be less of the RORB protein in specialized nerve cells in rabbits that have the mutation compared with rabbits that don't.

Those spinal cord nerve cells, called interneurons, help coordinate the left and right side of the body and are crucial for a normal gait, Andersson says. Without the RORB protein in interneurons, the rabbits may lack the ability to coordinate what their hind limbs are doing, which restricts their ability to hop.