The Bunny Hopping Syndrome (BHS1) / Spinal Dysraphism is an inherited disorder affecting the Weimaraner breed. The disease is characterized by the simultaneous movement or "bunny hopping" of the hind legs. Other signs include weakness and lack of coordination in the rear, while the front limbs remain coordinated and strong. Bunny hopping may occasionally be seen in the front legs. The disease is caused mutation which leads to malformations of the spinal cord during embryonic development.
In mammals, the nerves from one half of the brain control the opposite half of the body. This means that nerves from the left half of the brain innervate the right half of the body and vice versa. For movement control to function correctly, nerve pathways in the spinal cord must only ever run on one side of the body. However, In dogs with BHS1, this strict order is disrupted and nerve pathways in the spinal cord switch sides. As a result, affected dogs cannot control either the left or the right hind leg, and always hop with both legs. Because this gait resembles the hopping of a bunny, the disease is called Bunny Hopping Syndrome. In contrast to Shaking-Puppy-Syndrome in Weimaraner dogs, the gait of BHS1-affected puppies does not improve as they grow based on current knowledge. Consequently, euthanasia is often considered as a result.
